Java Programming Notes for Beginners by Arun Umrao

1
PROGRAMMING
JAVA
Arun Umrao
www.sdmsacademy.in
DRAFT COPY - GPL LICENSING

Contents
1 Introduction 7
1.1 Data In & Data Out . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.1.1 Print Output . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.1.2 Formatted Output . . . . . . . . . . . . . . . . . . . . . . 8
1.1.3 Escape Characters . . . . . . . . . . . . . . . . . . . . . . 10
1.1.4 Quotes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.1.5 Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.1.6 Variables & Data Type . . . . . . . . . . . . . . . . . . . 12
Boolean . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Character . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Byte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Short . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Integer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Float Decimals . . . . . . . . . . . . . . . . . . . . . . . . 14
Double Decimals . . . . . . . . . . . . . . . . . . . . . . . 15
Declaration, Initialization & Assignment . . . . . . . . . . 15
Signed & Unsigned Integer . . . . . . . . . . . . . . . . . 16
Overflow of Data . . . . . . . . . . . . . . . . . . . . . . . 17
Cast Operators . . . . . . . . . . . . . . . . . . . . . . . . 17
Scope of Variables . . . . . . . . . . . . . . . . . . . . . . 18
1.1.7 Access Controll . . . . . . . . . . . . . . . . . . . . . . . . 19
private . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
package . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
protected . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
public . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.2 Java Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.2.1 Expression . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.2.2 Unary Operaors . . . . . . . . . . . . . . . . . . . . . . . 19
1.2.3 Binary Relations . . . . . . . . . . . . . . . . . . . . . . . 20
1.2.4 Logical Relations . . . . . . . . . . . . . . . . . . . . . . . 22
1.2.5 Precedence of Relational Operators . . . . . . . . . . . . . 24
1.2.6 Bitwise Operator . . . . . . . . . . . . . . . . . . . . . . . 25
1.2.7 Shift Operator . . . . . . . . . . . . . . . . . . . . . . . . 27
1.2.8 Condition & Relation . . . . . . . . . . . . . . . . . . . . 29
3

4 CONTENTS
1.2.9 Arithmetic Operators . . . . . . . . . . . . . . . . . . . . 30
1.2.10 Precedence of Arithmatic Operators . . . . . . . . . . . . 31
1.2.11 Relational Operators . . . . . . . . . . . . . . . . . . . . . 32
1.3 Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
1.3.1 if condition . . . . . . . . . . . . . . . . . . . . . . . . . . 33
1.3.2 if-else condition . . . . . . . . . . . . . . . . . . . . . . . . 33
1.3.3 switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
1.4 Iteration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
1.4.1 for loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
1.4.2 while loop . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1.4.3 For Loop Like While Loop . . . . . . . . . . . . . . . . . . 38
1.5 Parsing Arguments . . . . . . . . . . . . . . . . . . . . . . . . . . 39
1.6 Mathematical Operator . . . . . . . . . . . . . . . . . . . . . . . 40
1.6.1 Trigonometric Functions . . . . . . . . . . . . . . . . . . . 40
cos, sin & tan . . . . . . . . . . . . . . . . . . . . . . . . . 40
acos, asin & atan . . . . . . . . . . . . . . . . . . . . . . . 41
cosh, sinh & tanh . . . . . . . . . . . . . . . . . . . . . . . 42
1.6.2 Logarithm Function . . . . . . . . . . . . . . . . . . . . . 42
exp, log . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
1.6.3 Arithmatic Function . . . . . . . . . . . . . . . . . . . . . 43
pow, sqrt, floor, ceil & round . . . . . . . . . . . . . . . . 43
2 String & Arrays 45
2.1 Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
2.2 Array . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
2.2.1 Dyanmic Array . . . . . . . . . . . . . . . . . . . . . . . . 46
2.2.2 Uni-dimensional Array . . . . . . . . . . . . . . . . . . . . 46
2.2.3 Multi-dimensional Array . . . . . . . . . . . . . . . . . . . 47
2.2.4 Size of Array . . . . . . . . . . . . . . . . . . . . . . . . . 48
2.3 Class, Object & Function . . . . . . . . . . . . . . . . . . . . . . 49
2.3.1 Arguments . . . . . . . . . . . . . . . . . . . . . . . . . . 53
2.3.2 Prototyping . . . . . . . . . . . . . . . . . . . . . . . . . . 54
2.3.3 this Reference . . . . . . . . . . . . . . . . . . . . . . . . . 54
2.3.4 Field Declaration . . . . . . . . . . . . . . . . . . . . . . . 55
2.3.5 Inheritance . . . . . . . . . . . . . . . . . . . . . . . . . . 55
2.3.6 Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
2.3.7 Type of Objects . . . . . . . . . . . . . . . . . . . . . . . 57
2.4 Threading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
2.4.1 Exception Handling . . . . . . . . . . . . . . . . . . . . . 62
3 Accessing System Files 63
3.1 Input Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
3.1.1 File Handling . . . . . . . . . . . . . . . . . . . . . . . . . 64
Open a File . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Close a File . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Reading File . . . . . . . . . . . . . . . . . . . . . . . . . 66

CONTENTS 5
Writing File . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Temporary File . . . . . . . . . . . . . . . . . . . . . . . . 67
Memory Mapped I/O . . . . . . . . . . . . . . . . . . . . 68
Random Access File . . . . . . . . . . . . . . . . . . . . . 69
File Pointer to Class . . . . . . . . . . . . . . . . . . . . . 71
3.1.2 File Directory . . . . . . . . . . . . . . . . . . . . . . . . . 71
Finding Roots . . . . . . . . . . . . . . . . . . . . . . . . 71
File Object . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Directory . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
3.2 JNI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

Chapter 1
Introduction
Here we have use Netbean IDE for java programming.
1.1 Data In & Data Out
In Java, input and output is received and sent through standard input and
output stream. The input is accepted via in stream while output is sent via out
stream. Java has strong grouping convention. Function or block domain are
limited by curly braces, ie {...}. All the variable defined inside the {...} have
local scope. A semicolon is used to terminate the line.
1.1.1 Print Output
We can print the output in out stream via system i/o class. Se example below,
in which “Hi” is printed in output stream.
✞
1 package jscript;
/*Jscript is main class name. It shall be same as*
3 *file name. i.e. file name must be jscript.java*/
public class Jscript {
5
public static void main(String[] args) {
7 System.out.println("Hi");
}
9 }
✆
✞
Hi
✆
When a java program is run, it starts execution from the main() function.
This main() function is defined here as public so that it can be executed from
anywhere. Its return type is void, i.e. no return value. In the following line
✞
1 public static void main(String[] args) {}
✆
7

8 CHAPTER 1. INTRODUCTION
(String[] args) receives the string array from the commandline. Number of input
arrays are counted by using length object. In java, class name shall be same as
its file name where it is declared. Here println is similar to the printf of C.
1.1.2 Formatted Output
In Java, values or variables can be placed inside the string by using ‘+’ sign as
shown in example below.
✞
1 package jscript;
5
7 System.out.println("Hi "+10+" .");
}
9 }
✆
✞
Hi 10 .
✆
Here, println is short form of print a line and it prints the string at output
stream. printf is short form of print formatted and it can be used in place of
println for formatted output.
✞
1 package jscript;
5 public class Jscript {
7 public static void main(String[] args) {
System.out.printf("Hi %d.n", 10);
9 }
}
✆
✞
Hi 10.
✆
In Java, modifiers are used to print formatted outputs. A modifier ‘%s’ simply
puts the string by creating space equal to the length of string. If this modifier
is redefined like ‘%20s’ (a positive integer between % and ‘s’ symbols), then
space for 20 characters is created. If string length is less than 20 characters
then ‘ ’ (space) is prefixed to the string to increase its length to 20. If number
in modifier is less than the length of string then nothing is done.
✞
1 package jscript;

1.1. DATA IN & DATA OUT 9
Symbolic Constant Represents
%a Floating-point number, hexadecimal digits and p-
notation.
%A Floating-point number, hexadecimal digits and P-
notation.
%c Single character.
%d Signed decimal integer.
%e Floating-point number in e-notation form.
%E Floating-point number in e-notation form.
%f Floating-point number in decimal notation form.
%g If the exponent is less than 4 or greater than or equal
to the precision %e used otherwise %f is used.
%G If the exponent is less than 4 or greater than or equal
to the precision %E used otherwise %F is used.
%i Signed decimal integer.
%o Unsigned octal integer.
%p A pointer.
%s Character string.
%u Unsigned decimal integer.
%x Unsigned hexadecimal integer using hex digits 0f.
%X Unsigned hexadecimal integer using hex digits 0F.
%% Prints a percent sign.
Table 1.1: Conversion specifiers.

System.out.printf(""%s" secured numbers "%d"n", "Arun Kumar"
, 100);
7 System.out.printf(""%20s" secured numbers "%5d"n", "Arun
Kumar", 100);
}
9 }
✆
✞
"Arun Kumar" secured numbers "100"
" Arun Kumar" secured numbers " 100"
✆
For numeric modifiers, total spaces and filled space can also be used simulta-
neously if modifier is modified like ‘%10.6d’. Here number ‘10’ will create 10
spaces for placing a number and if digits in number is less than ‘6’ then ‘0’ will
be prefixed with the number.
✞
package jscript;
2
4
6 int i;
System.out.printf("%5s%10s%10sn", "Num", "Square", "Cubic");
8 for (i = 90; i < 92; i++) {
System.out.printf("%5d%10d%10dn", i, i * i, i * i * i);
10 }
}
12 }
✆
✞
Num Square Cubic
90 8100 729000
91 8281 753571
✆
1.1.3 Escape Characters
Escape characters are used to perform action even if they are used as string.
For example
✞
1 package jscript;
System.out.println("Rajasthan");
7 }
}
✆
n at the end of println function would add a new line after “Rajasthan!”. The
output of the program is

✞
Rajasthan
✆
Other escape characters are
Escape Character Meaning
t Adding a tab
n Start a new line
1.1.4 Quotes
In Java, double quotes is used to represents a group of character as a string.
Single quote represents to character code in decimal equivalent.
✞
package jscript;
2 /*Jscript is main class name. It shall be same as*
*file name. i.e. file name must be jscript.java*/
System.out.println("Uttar Pradesh.");
8 }
}
✆
✞
Uttar Pradesh.
✆
✞
1 package jscript;
char a = ’a’;
7 System.out.println(a);
}
9 }
✆
✞
a
✆
1.1.5 Comments
Commenting is most useful feature of the Java programming. It is used to write
comments before or after a function or variable. Stuff within the commenting
delimiters is ignored during compilation of the program. There are two type
of commenting delimiters. First, single line commenting delimiter and second,
multi-line commenting delimiter. For single line commenting ‘//’ is used and
for multi-line commenting ‘/* ... */’ is used.

✞
1 /*
* Multiline comments
3 */
package jscript;
5
7
9 //Print cost of pen
System.out.println("Cost of pen is "+10);
11 }
}
✆
The output of above program is
✞
Cost of pen is 10
✆
1.1.6 Variables & Data Type
Variables are multicharacter names used to refer to some locations in memory
that holds a value to which we are working. A variable is equivalent to its
assigned value. A variable may be alphanumeric name with underscope charac-
ter. First numeric character of a variable name is not acceptable. Spaces and
special characters which are reserved for internal operations of Java are illegal.
Similarly, use of comma, dot, symbol of question mark, symbols reserved for
realtion operations, symbols reserved for bitwise operations, colon and line ter-
minating symbol are also considered as illegal if used in variable names. Key
words specially reserved for internal programming of Java, can not be used like
variable name. A list of reserved keyword is given in section ??.
✞
1 int A1; // Legal and acceptable.
int 1A; // Illegal, first character is numeric
3 int A_1;// Legal, _ is acceptable
int A$1;// Legal, $ is not reserved character
5 int A 1;// Illegal, space is not acceptable
int for;// Illegal, for is reserved keyword
✆
A variable declared once can not be declared again.
Boolean
Java has dedicated boolean type. Its value is either true or false.
✞
package jscript;
2
4

6 System.out.println("Function is " + false);
}
8 }
✆
✞
Function is false
✆
Character
char is used to initialize a 18 bit unsigned unicode character.
✞
1 char *<var name>=<char code>;
✆
A char variable without initialization is not acceptable in java.
✞
1 package jscript;
char A1=100;
7
System.out.println("Char is " + A1);
9 }
}
✆
✞
Char is d
✆
Byte
It is one byte long integer value.
✞
1 package jscript;
byte i = 120;
7 System.out.println("i is " + i);
}
9 }
✆
✞
i is 120
✆
If the variable ‘i’ is assigned the integer value larger than 8 bits then compiler
shows error and refuse to compile the program.

Short
It is two byte long integer value.
✞
1 package jscript;
byte i = 510;
}
9 }
✆
✞
i is 510
✆
If the variable ‘i’ is assigned the integer value larger than 16 bits then compiler
shows error and refuse to compile the program.
Integer
A 4 byte long numerical value is declared and initialized by using primitive data
type int. If an integer variable is initialized as decimal number, then compiler
refuse to compile the program.
✞
1 int <var name>;
int <var name>=<value>;
✆
✞
package jscript;
2
4
6 int i=10;
System.out.println("i is " + i);
8 }
}
✆
✞
i is 10
✆
Float Decimals
This data type is floating-point type. It usually referred to as a single-precision
floating-point. Float-to-integer or integer-to-float type conversion of numbers
take place by casting the number. It is 4 byte long. Its range is from 1.2×10−38
to 1.2 × 1038
. Syntax for the float data type is

✞
1 float <var name>;
float <var name>= (float) <decimal value>;
✆
See the example below.
✞
package jscript;
2
4
6 float i = (float) 10.126;
8 }
}
✆
✞
i is 10.126
✆
Double Decimals
This data type is floating-point type. It usually referred to as a double-precision
floating-point. Double-to-integer or integer-to-double type conversion of num-
bers take place by casting the number. It is 8 bytes long. Its range is from
2.3 × 10−308
to 2.3 × 10308
. Syntax for the double data type is
✞
1 double <var name>;
double <var name>=<decimal value>;
✆
See the example below.
✞
package jscript;
2
4
6 double i = 1.12416;
8 }
}
✆
✞
i is 1.12416
✆
Declaration, Initialization & Assignment
A variable in Java can be assigned as integer, if syntax is defined as given below:
✞
1 int variable_name;
✆

It means there is some space declared in data to store integer value. Multiple
variables can be assigned in single line or successive way like
✞
1 int variable_a, variable_b, variable_c;
✆
A variable in Java is said to be initialized if a numeric or an alphabatic value is
assigned to it. For example variable a is initialized by
✞
1 int variable_a = <value>;
✆
To distinct the words of a variable, underscore symbol (‘ ’) is used. Anytime
within a program in which we specify a value explicitly instead of referring
to a variable or some other form of data, that value is referred as a literal.
Literals can either take a form defined by their type, or one can use hexadecimal
(hex) notation to directly insert data into a variable regardless of its type. Hex
numbers are always preceded with ‘0x’. The length of data type is measured its
byte length. The datatype may be signed or unsigned. In signed data type, the
MSB is used for sign declaration and rest of the bits are used for data value. In
unsigned data type, all the bits are used for data value.
✞
1 package jscript;
int i = 0x50;
}
9 }
✆
✞
i is 80
✆
Signed & Unsigned Integer
A byte is 8 bit long. The size of int is 4 byte, i.e. 32 bits. A signed integer is
that integer whose first bit, i.e. MSB is taken as sign bit. If integer is defined
as signed then MSB is sign bit and remaining 31 bits are used for storing an
integer. If integer is defined as unsigned then all 32 bits are used for storing an
integer.
✞
1 //+---------------------Sign bit
(1)1111111b =>-127d // Signed 7 bit integer
3 11111111b => 255d // Unsigned 8 bit integer
✆
A signed integer ranges from -2147483647 to 2147483647 while unsigned integer
ranges from 0 to 4294967294. In the Java, bit ‘0’ is used as positive sign and
bit ‘1’ is used as negative sign.

Overflow of Data
A variable declared as integer, long, float or double integer and character has
capacity to store a specific size of data. An integer variable can not store data
as long as float variable. This is why, a variable shall be declared of proper size
for storing a data. To understand the overflow, consider a virtual datatype that
can store only one byte long data. This datatype may be signed or unsiged.
First assume it is unsigned, then the largest decimal value, that can be stored
by it is 255. Initially, datatype has initialized with decimal value 254.
✞
1 datatype k = 254d = 11111110b
✆
datatype is incremented by 1, it becomes
✞
1 datatype k = 255d = 11111111b
✆
Again, datatype is incremented by 1, it becomes
✞
1 datatype k = 255d = 1 00000000b
✆
The size of result is larger than one byte. The value of datatype reset to zero
due to overflow. Here, overflow carry is ‘1’. Similarly a positive signed value
becomes negative signed value if it is incremented beyond the signed data range.
Taking the same datatype with signed value.
✞
1 /* Bit inside parentheses represents to sign.*/
datatype k = 127d = (0)1111111b
✆
It is incremented by 1, it becomes
✞
/* Bit inside parentheses represents to sign.*/
2 datatype k = -0d = (1)0000000b
✆
It becomes negative zero. Again, if increment by 1, the result is
✞
/* Bit inside parentheses represents to sign.*/
2 datatype k = -1d = (1)0000001b
✆
Which is -1. Here, again datatype variable is overflowed. In java, overflow values
shows errors and program is not compiled.
Cast Operators
Cast operators are used in conversion of one type data into other type data.
Type casting may be of two types: (i) Implicit type casting and (ii) Explicit
type casting. Implicit type casting is automatically handled by compiler i.e.
when two or more data types are under execution. The final data-type will be
that data type which is declared. An explicit type cast is a cast that should we
specifically invoked with either of the cast. The compiler does not automatically
invoke to resolve the data type conversion.

✞
package jscript;
2
4
6 float i = (int) 10.2;
8 }
}
✆
Here, at first, 10.2 is converted into integer by truncating its decimal part and
then it is converted into float data type. Hence the 10.0 shall be final output of
above program.
✞
i is 10.0
✆
String can be converted to character array by using toCharArray() method.
✞
1 /*Convert string into char code.*/
char[] c = s.toCharArray();
✆
Here, ‘c’ represents to character array.
A string is converted into string array by using split() method. To split
string by space, synopsis is used like
✞
String[] sArray=s.split(" ");/*Space by " "*/
✆
To split the string from each character, split() method is used like
✞
1 String[] sArray=s.split("");/*No space by ""*/
✆
✞
1 package jscript;
5 public static void main(String args[]) {
String str = "This is my room";
7 String[] k = str.split(" ");
System.out.printf("i is in string : %sn", k[0]);
9 }
}
✆
✞
i is in string : This
✆
Scope of Variables
Local variables are undefined prior to initialization. We can declare a variable
without initialization. But if it is try to use local variables before assigning a
value, the compiler will refuse to compile the program.

1.2. JAVA OPERATORS 19
1.1.7 Access Controll
All members of a class are accessible to the class itself. To control access from
other classes, class members have four possible access modifiers:
private
Private members declared private and they are accessible only in the same class.
package
Package members declared with no access modifier are accessible in classes in
the same package, as well as in the class itself.
protected
Protected members declared protected are accessible in subclasses of the class,
in classes in the same package, and in the class itself.
public
Public members declared public are accessible anywhere the class is accessible.
The private and protected access modifiers apply only to members not to the
classes or interfaces themselves. For a member to be accessible from a section of
code in some class, the member’s class must first be accessible from that code.
1.2 Java Operators
There are following types of Java operators.
1.2.1 Expression
An expression is a combination of one or more explicit values, constants, vari-
ables, operators, and functions. The evaluated value of expression is assigned
to another variable or printed in output stream. A function declared as void
type returns void value the this return value is discarded in an expression.
1.2.2 Unary Operaors
In a unary operation, operator has only one operand. The unary operators used
in Java are given in table below.

Table 1.2: Unary operators.
Type Representation
Increment ++x, x++
Decrement - - x, x - -
Positive +x
Negative -x
Ones‘ complement ∼ x
Logical negation !x
Cast (type-name) cast-expression
✞
1 package jscript;
int i=10;
7 System.out.println("Name of tree is " + (-i));
}
9 }
✆
✞
Name of tree is -10
✆
1.2.3 Binary Relations
Binary operators are those operators which require two operands. These oper-
ators are addition, subtraction, multiplication, division, less than, greater than,
equals to etc. The relational binary operators are
1. < known as less than.
2. > known as greater than.
3. ≤ known as less than or equal to.
4. ≥ known as greater than or equal to.
5. == known as equals.
6. ! = known as not equals.

✞
1 package jscript;
int a = 10;
7 int b = 20;
int c = 5;
9 if (a < b) {
System.out.println(a + " is less than " + b);
11 }
if (a > b) {
13 System.out.println(a + " is greater than " + b);
}
15 if (a <= c) {
System.out.println(a + " is less than or equal to " + c);
17 }
if (a == c) {
19 System.out.println(a + " is exactly equal to " + c);
}
21 if (a != b) {
System.out.println(a + " is not equal to " + b);
23 }
}
25 }
✆
Output of above program is
✞
10 is less than 20
10 is not equal to 20
✆
Remember that ‘=’ and ‘==’ are not same. For example, ‘c=20’ assigned
the value 20 to variable c and returns true in output rather than comparison of
c and 20. Reason behind is that c does not have a dedicated boolean type. So
‘0’ means false and anything else is true. In Java, the coditions like
✞
int a = 20; //constant initialized
2 if (a = 10) //incompatible integer type
System.out.println("Stuff");
✆
✞
1 if (0 < v < 10) {//bad operand type for <
System.out.println("Stuff");
3 }
✆
are not acceptable. The compiler shows error expressing ‘incompatible integer
type’ or ‘bad operand type for <’. The appropriate form of comparison is shown
in below example.
✞
1 package jscript;

int v = 7;
7 if (v == 7) {
System.out.println("v is " + v);
9 }
}
11 }
✆
✞
v is 7
✆
✞
1 package jscript;
int v = 7;
7 if (0 < v && v < 10) {
System.out.println("v=" + v +" is less than 20");
9 }
}
11 }
✆
✞
v=7 is less than 20
✆
1.2.4 Logical Relations
Logical relations sometimes known as boolear relations also. Logical operators
are those operators which compare the variables or results logically.
1. && known as logical AND. If both the operands are non-zero, then con-
dition becomes true.
2. || known as logical OR. If any of the two operands is non-zero, then con-
dition becomes true.
3. ! known as logical NOT. Use to reverses the logical state of its operand.
If a condition is true then Logical NOT operator will make false.
✞
1 package jscript;

System.out.printf("6 != 6 && 6 / 2 < 5 is %bn", 6 != 6 && 6 / 2
< 5);
7 System.out.printf("6 != 6 || 6 / 2 < 5 is %bn", 6 != 6 || 6 / 2
< 5);
System.out.printf("6 != 6 is %bn", 6 != 6);
9 }
}
✆
✞
6 != 6 && 6 / 2 < 5 is false
6 != 6 || 6 / 2 < 5 is true
6 != 6 is false
✆
Logical expressions are evaluated from left to right. Evaluation stops as soon
as something is discovered that renders the expression false.
✞
1 package jscript;
System.out.printf("(2 < 3) && (4 > 5) is %bn", (2 < 3) && (4 >
5));
7 System.out.printf("(2 < 3) && (4 < 5) is %bn", (2 < 3) && (4 <
5));
}
9 }
✆
✞
(2 < 3) && (4 > 5) is false
(2 < 3) && (4 < 5) is true
✆
✞
package jscript;
2
4
6 int x = 6;
/* Here x is equal to 6. So, the relation*
8 * x != 6 is false. Now second relation*
* x / 2 < 5 is not evaluated here. So, *
10 * the result is 0. */
System.out.printf("Expression result is %bn", x != 6 && x / 2 <
5);
12 }
}
✆
✞
Expression result is false
✆

✞
1 package jscript;
int x = 4;
7 /* Here x is not equal to 6. So, that *
* x != 4 is true. Now second relation*
9 * x / 2 < 5 is logically ANDED with *
* the result of x != 6. Here x/2 is 2*
11 * and 2 is less than 5, so logical *
* AND of left and right values is 1 */
13 System.out.printf("Expression result is %bn", x != 6 && x / 2 <
5);
}
15 }
✆
✞
Expression result is true
✆
1.2.5 Precedence of Relational Operators
The precedence of the binary relational operators is less than that of the arith-
metic operators. This means, for example, x > y + 2 is same as x > (y + 2) and
x = y > 2 is same as x = (y > 2). It means, in an expression, order of evalu-
ation of operators is arithamtic operators, relational operators and assignment
operators respectively.
✞
1 package jscript;
int x = 4, y = 1;
7 /*x > y + 2*/
/*x > 1 + 2*/
9 /*x > 3 */
/*4 > 3 (true)*/
11 if (x > y + 2) {
System.out.println("Expression Passed.");
13 } else {
System.out.println("Expression Failed.");
15 }
}
17 }
✆
✞
Expression Passed.
✆

1.2.6 Bitwise Operator
A bitwise OR (|) gives result ‘1’ if either one or both bits are ‘1’ otherwise result
is zero. A bitwise AND (&) gives result ‘1’ if both bits are ‘1’ otherwise result is
zero. A bitwise XOR (ˆ) results ‘1’ if only either of two bits1
are ‘1’ otherwise
result is zero. A bitwise NOT (∼) or complement, is a unary operation that
performs logical negation on each bit, forming the ones’ complement of the given
binary value. Bits those are 0 become 1, and those that are 1 become 0.
✞
1 package jscript;
/*10 is Binary equivalent to 1010*/
7 int i = 10;
/*5 is Binary equivalent to 0101*/
9 int j = 5;
/*-------------------------**
11 Bitwise OR Operation is
1010
13 0101
------
15 1111 = 15
**------------------------*/
17 System.out.println("Bitwise OR of " + i + ", " + j + " is " + (i
| j));
/*-------------------------**
19 Bitwise AND Operation is
1010
21 0101
------
23 0000 = 0
**------------------------*/
25 System.out.println("Bitwise AND of " + i + ", " + j + " is " + (i
& j));
/*-------------------------**
27 Bitwise XOR Operation is
1010
29 0101
------
31 1111 = 15
**------------------------*/
33 System.out.println("Bitwise XOR of " + i + ", " + j + " is " + (i
^ j));
/*-------------------------**
35 Bitwise NOT Operation is
1010
1
If both bits are opposite bits.

37 ---------
0101 = -11
39 **------------------------*/
System.out.println("Bitwise NOT of " + i + " is " + (~i));
41 }
}
✆
✞
Bitwise OR of 10, 5 is 15
Bitwise AND of 10, 5 is 0
Bitwise XOR of 10, 5 is 15
Bitwise NOT of 10 is -11
✆
Normally, bitwise & operator returns the value equal to or less than the lesser
operand. This is why & operator is used to restric the upper limit of the random
result.
✞
package jscript;
2
4
6 int i = 0;
while (i < 10) {
8 System.out.println("i&" + i + " => " + (i & 5));
i++;
10 }
}
12 }
✆
✞
0&5 => 0, 1&5 => 1, 2&5 => 0, 3&5 => 1, 4&5 => 4,
5&5 => 5, 6&5 => 4, 7&5 => 5, 8&5 => 0, 9&5 => 1,
✆
While bitwise | operator returns the value equal to or larger than the largest
operand. This is why | operator is used to restrict the lower limit of random
result.
✞
package jscript;
2
4
6 int i = 0;
while (i < 10) {
8 System.out.println("i|" + i + " => " + (i | 5));
i++;
10 }
}
12 }
✆

✞
0|5=>5, 1|5=>5, 2|5=>7, 3|5=>7, 4|5=>5
5|5=>5, 6|5=>7, 7|5=>7, 8|5=>13, 9|5=>13
✆
1.2.7 Shift Operator
Logical shift operators are
1. << known as left shift
2. >> known as right shift
✞
package jscript;
2
4
6 /*Bit pattern of Decimal 4 is equivalent to binary 100*/
int i = 4;
8 /*Number of places take place by binary shift.*/
int j = 2;
10 /*<< makes 100 to 10000, i.e. 16 in decimal*/
System.out.println("<< of " + i + ", " + j + " is " + (i << j));
12 /*>> makes 100 to 1, i.e. 1 in decimal*/
System.out.println(">> of " + i + ", " + j + " is " + (i >> j));
14 }
}
✆
✞
<< of 4, 2 is 16.
>> of 4, 2 is 1.
✆
In the following example, bitwise relation is used to add two number.
✞
package jscript;
2
4
6 int x = 30, y = 1, sum, carry;
/*---------------------------**
8 Decimal 30 is binary 11110
Decimal 01 is binary 00001
10 OR Operation is
11110
12 00001
----------
14 S= 11111
**---------------------------*/
16 sum = x ^ y;

/*---------------------------**
18 Decimal 30 is binary 11110
Decimal 01 is binary 00001
20 OR Operation is
11110
22 00001
--------
24 C = 00000
**---------------------------*/
26 carry = x & y;
/*Performed loop until last carry is not zero.*/
28 while (carry != 0) {
/*----------------------------------------**
30 Left shift of carry is
C_s = 000000
32 This operation is performed to shift
the carry left hand side by one place
34 to add it with next higher place value.
**----------------------------------------*/
36 carry = carry << 1;
/*Take x as sum value from OR Operation.*/
38 x = sum;
/*Take y as carry value form *
40 *left shift of AND Operation.*/
y = carry;
42 /*Take OR Operation of x and y*/
sum = x ^ y;
44 /*Get the next carry.*/
carry = x & y;
46 }
/*Print the sum 31.*/
48 System.out.println("Sum of " + x + " and " + y + " is : " + sum);
}
50 }
✆
✞
Sum of 30 and 1 is 31
✆
Binary shift operation can be performed in characters and strings. It is explained
in the example given below.
✞
1 package jscript;
char a = ’a’;/*Binary equivalent-1100001*/
7 char b = ’b’;/*Binary equivalent-1100010*/
char c = ’c’;/*Binary equivalent-1100011*/
9 /*-------------------------------------------------------*
Shift of a by 16 bit left side--11000010000000000000000

11 Shift of b by 8 bit left side-----------110001000000000
Shift of c by 0 bit left side-------------------1100011
13 -------------------------------------------------------
OR Operation -------------------11000010110001001100011
15 It is equivalent to Decimal---------------------6382179
*-------------------------------------------------------*/
17 System.out.println("Left binary bit shift " + (a << 16 | b << 8 |
c));
}
19 }
✆
✞
Left binary bit shift is 6382179
✆
The unary operator ‘∼’ returns the one’s complements of an integer by changing
bit ‘0’ into ‘1’ and viceversa.
✞
1 package jscript;
int j = 0;
7 System.out.println("Bitwise ~ operation on an integer.");
while (j < 3) {
9 System.out.println(j + " => " + (~j));
j++;
11 }
}
13 }
✆
✞
Bitwise ~ operation on an integer.
0 => -1
1 => -2
2 => -3
✆
1.2.8 Condition & Relation
If a condition is true then successive value is taken otherwise next value. The
simplest form of this operator is
✞
x ? y : z
✆
✞
1 package jscript;
int i = 1, j = 0;

7 while (j < 3) {
System.out.println(i + " < " + j + " " + (i < j ? "YES" : "NO"
));
9 j++;
}
11 }
}
✆
✞
1 < 0 NO
1 < 1 NO
1 < 2 YES
✆
1.2.9 Arithmetic Operators
Arithmetic operators are
1. + known as addition operator. It adds the right value with left value.
2. − known as subtraction operator. It subtracts the right value from left
value.
3. / known as division operator. It divides the left value with right value.
Returns the quotient. If, both left and right values are integer then decimal
part of the result is truncated.
4. ∗ known as multiplication operator. It multiply the left value with right
value. Returns product of two numbers.
5. % known as modulo operator. Returns the remainder in division.
6. = known as assignment operator. A variable at left side to it is assigned
the value at the right side of it.
✞
1 package jscript;
float i = 1, j = 3;
7 System.out.println(i + " + " + j + "=" + (i + j));
System.out.println(i + " - " + j + "=" + (i - j));
9 System.out.println(i + " * " + j + "=" + (i * j));
System.out.println(i + " / " + j + "=" + (i / j));
11 System.out.println(i + " % " + j + "=" + (i % j));
}
13 }
✆

✞
1.0 + 3.0=4.0
1.0 - 3.0=-2.0
1.0 * 3.0=3.0
1.0 / 3.0=0.33333334
1.0 % 3.0=1.0
✆
1.2.10 Precedence of Arithmatic Operators
Arithmatic problems are not solved from left to right in the sequence the expres-
sion is written. But some rules are used. For example, parentheses are solved
first, then division, multiplication, addition and subtraction. Thus, arithmatic
operators have some precedence. Operators in order of decreasing precedence
are given in table below.
Operators Associativity
() Left to right
+ – (unary) Right to left
* / Left to right
+ – (binary) Left to right
= Right to left
✞
1 package jscript;
int y;
7 /* Order of arithmatic operators *
* are /, *, +, -, =. So first 12*
9 * is divided by 5 and answer is *
* 2.4. 6 is multiply by 2.4 and *
11 * result is 14.4. It is added to*
* 20 and 10 is subtracted *
13 * The answer is 14.4+20-10=24.4 */
y = 6 * 12 / 5 + 20 - 10;
15 /* In result only 24 is printed. *
* Decimal is truncated. */
17 System.out.println("Expression result is " + y);
}
19 }
✆
✞
Expression result is 24
✆

1.2.11 Relational Operators
The assignment operators are
1. == known as equal.
2. ∗ = known as product and equal.
3. / = known as divide mode and equal.
4. + = known as add and equal.
5. − = known as subtract and equal.
6. <<= known as left shift and equal.
7. >>= known as right shift and equal.
8. & = known as AND and equal.
9. ˆ= known as exclusive OR and equal.
10. | = known as inclusive OR and equal.
✞
1 package jscript;
int y = 2;
7 y += 2;
System.out.println("y += 2 is " + y);
9 y &= 2;
System.out.println("y &= 2 is " + y);
11 y ^= 2;
System.out.println("y ^= 2 is " + y);
13 y |= 2;
System.out.println("y |= 2 is " + y);
15 y <<= 2;
System.out.println("y <<= 2 is " + y);
17 }
}
✆
✞
y += 2 is 4
y &= 2 is 0
y ^= 2 is 2
y |= 2 is 2
y <<= 2 is 8
✆

1.3. CONDITIONS 33
1.3 Conditions
Conditions are the comparison statements those controls the execution of codes
inside the conditional blocks.
1.3.1 if condition
if () provides a way to instruct the program to execute a block of code only if
certain conditions have been met. The syntax of if () construct is
✞
1 if(/*conditions*/) // if condition is true then
statement // execute the condition.
✆
A simple example is
✞
package jscript;
2
4
6 int i=0;
while (i < 5) {
8 if (i == 2) {
System.out.printf("i is %dn", i);
10 }
i++;
12 }
}
14 }
✆
✞
i is 2
✆
1.3.2 if-else condition
if-else provides a way to instruct the program to execute a block of code only
if certain conditions have been met otherwise execute other block. The syntax
of if-else construct is
✞
1 if(/*conditions*/) // if condition is true then
statement one // execute the statement one.
3 else // otherwise if condition is false
statement two // execute the statement two.
✆
A simple example is
✞
package jscript;
2
4

6 int i=0;
while (i < 5) {
8 if (i == 2) {
10 } else {
System.out.printf("i is NOT %dn", 2);
12 }
i++;
14 }
}
16 }
✆
✞
i is NOT 2
i is NOT 2
i is 2
i is NOT 2
i is NOT 2
✆
A short hand for of if-else condition is
✞
1 int a=(b > c) ? d : e;
✆
Above statement is similar to the statement of “return d if b is greater than c
else return e”. if - else - if - else - if - else statement can be used successively.
1.3.3 switch
Use of a long chain of if-else-if-else-if-else is very complex and less readable.
There’s a solution by using the Switch-Case construct. The basic syntax of this
construction is given below.
✞
1 switch (<case variable>) {
case 1:
3 statements one
break;
5 case 2:
statements two
7 break;
case 3:
9 statements three
break;
11 default:
default statement
13 break;
}
✆
Here default case is executed if none of the cases is matched with case variable
value. Following is working example

1.3. CONDITIONS 35
✞
package jscript;
2
4
6 int i = 0;
while (i < 5) {
8 switch (i) {
case 1:
10 System.out.printf("i is %dn", i);
break;
12 case 2:
14 break;
case 3:
16 System.out.printf("i is %dn", i);
break;
18 default:
System.out.printf("either i<1 or i>3n");
20 break;
}
22 i++;
}
24 }
}
✆
✞
either i<1 or i>3
i is 1
i is 2
i is 3
either i<1 or i>3
✆
Here operator ‘break’ plays an important role. If break operator is not used
in block of ‘case’ then all the successive blocks are executed successively. The
reason behind is that, ‘break’ inside the ‘case’ exits from the switch block from
the current loop.
✞
1 package jscript;
int i = 0;
7 while (i < 5) {
switch (i) {
9 case 1:
11 case 2:

13 case 3:
15 break;
default:
17 System.out.printf("either i<1 or i>3n");
break;
19 }
i++;
21 }
}
23 }
✆
✞
either i<1 or i>3
i is 1
i is 1
i is 1
i is 2
i is 2
i is 3
either i<1 or i>3
✆
1.4 Iteration
Iteration is a process in which code statements are executed more than once.
For example, to print a line ten times, either the line is writem ten times one
after another or a loop is used to print the line ten times. Most common
iteration/loop functions are for and while.
1.4.1 for loop
The syntax of for loop is
✞
for(initialization; test; increment) {
2 /* code */
}
✆
The working example is
✞
1 package jscript;
int a, b;
7 b = 15;
for (a = 10; a < b; a++) {
9 System.out.printf("The number a is %d.n", a);
}

1.4. ITERATION 37
11 }
}
✆
The output is
✞
The number a is 10.
The number a is 11.
The number a is 12.
The number a is 13.
The number a is 14.
✆
The initialization statement is executed exactly once. It is used to assign an
initial value to some variable. The test expression is evaluated each time before
the code in the for loop executes. If this expression evaluates as 0 (false), the
loop is not (re)enter into the for loop. And execution of program carry on to
the code immediately following the for loop. If the expression is non-zero (ie
true), the loop is (re)enter inside the for loop. After each iteration of the loop,
the increment statement is executed. This often is used to increment the loop
index. An infinite loop is executed if for is defined as shown below.
✞
1 for(;;) {
/* statements / codes */
3 }
✆
Multiple initialization can be used by separating them by comma.
✞
1 for(initialization one, /*First var initialized*/
initialization two; /*Second var initialized*/
3 test of initializers;/*Test the condition of variables*/
increment one , /*Increment of first variable*/
5 increment two) { /*Increment of second variable*/
7 /* expressions / statements / codes */
9 }
✆
✞
1 package jscript;
int i, j;
7 for (i = 6, j = 1; j < i; i++, j = (j + 2)) {
System.out.printf("Product of i=%d & j=%d is %dn", i, j, i *
j);
9 }
}
11 }
✆

✞
Product of i=6 & j=1 is 6
✆
1.4.2 while loop
A while() loop is the most basic type of loop. It will run as long as the condition
retun non-zero (ie true) value. At false state, while loop exits.
✞
1 package jscript;
int i = 0;
7 while (i < 5) {
System.out.printf("i*i is %dn", i * i);
9 i++;
}
11 }
}
✆
✞
i*i is 0
i*i is 1
i*i is 4
i*i is 9
i*i is 16
✆
1.4.3 For Loop Like While Loop
The syntax of for loop as
✞
1 for(; <test> ; )
✆
is similar to the while loop
✞
1 while (<test>)
✆
Following is an example which shows that for loop is similar to the while loop.
✞
1 package jscript;
int i = 0;

1.5. PARSING ARGUMENTS 39
7 for (; i < 5;) {
System.out.printf("%dt", i);
9 i++;
}
11 System.out.printf("n");
int j = 0;
13 while (j < 5) {
System.out.printf("%dt", j);
15 j++;
}
}
19 }
✆
✞
0 1 2 3 4
0 1 2 3 4
✆
1.5 Parsing Arguments
When a program is being executed via another program internally, arguments
are required to be passed to the executable ie the program. These arguments
are considered as inputs for the executable. To pass the values we define main()
function as
✞
public static void main(String[] args)
✆
Here ‘args’ are the array of input strings.
✞
1 package jscript;
3 class Jscript {
5 public static void main(String args[]) {
System.out.println(args[1]);
7 }
}
✆
After compiling and executing the executable as
✞
Jscript.jar a b c
✆
Output is
✞
a
✆
Here Jscript.jar in commandline is also considered as an argument. This is
why there are four arguments and first argument, ie 0th
argument, is Jscript.jar
itself and rest of the arguments are a, b and c respectively.

1.6 Mathematical Operator
In C programming addition, subtraction, multiplication and division mathemat-
ical operators can be directly used. Modulus is another mathematical operators
that gives the remainder value. Application of these operators are a + b, a − b,
a ∗ b, a/b and a%b respectively.
✞
1 package jscript;
float i = 1, j = 3;
7 System.out.println(i + " + " + j + "=" + (i + j));
System.out.println(i + " - " + j + "=" + (i - j));
9 System.out.println(i + " * " + j + "=" + (i * j));
System.out.println(i + " / " + j + "=" + (i / j));
11 System.out.println(i + " % " + j + "=" + (i % j));
}
13 }
✆
✞
1.0 + 3.0=4.0
1.0 - 3.0=-2.0
1.0 * 3.0=3.0
1.0 / 3.0=0.33333334
1.0 % 3.0=1.0
✆
1.6.1 Trigonometric Functions
“math.h” preprocessor file provides the mathematical functions that can be used
directly in the program. Some of them are defined in following sections.
cos, sin & tan
The cos, sin, and tan functions return the cosine, sine, and tangent of the
argument, expressed in radians. The domain of arguments of sin, cos and tan
are [−π/2, π/2], [0, π] and [−π/2, π/2] respectively. The numerical range of sin,
cos and tan are [−1, 1], [−1, 1] and [−∞, ∞].
✞
1 double cos(double x);
double sin(double x);
3 double tan(double x);
✆
A simple example is
✞
1 package jscript;

1.6. MATHEMATICAL OPERATOR 41
System.out.printf("Cosine at 22/7 radian is : %f n", Math.cos(22
/ 7));
7 System.out.printf("Sine at 22/7 radian is : %f n", Math.sin(22 /
7));
System.out.printf("Tangent at 22/7 radian is : %f n", Math.tan
(22 / 7));
9 }
}
✆
✞
Cosine at 22/7 radian is : -0.989992
Sine at 22/7 radian is : 0.141120
Tangent at 22/7 radian is : -0.142547
✆
acos, asin & atan
The acos() functions return the arccosine of their arguments in radians, and the
asin() functions return the arcsine of their arguments in radians. All functions
expect the argument in the range [−1, +1]. The arccosine returns a value in
the range [0, π]; the arcsine returns a value in the range
h
−
π
2
,
π
2
i
. The atan()
returns their argument value in radian in the range
h
−
π
2
,
π
2
i
. Method of use of
inverse function in following systems.
✞
1 double asin(double x);
double acos(double x);
3 double atan(double x);
✆
A simple example is
✞
1 package jscript;
System.out.printf("Arc cosine at argument 0.5 is : %f n", Math.
acos(0.5));
7 System.out.printf("Arc sine at argument 0.5 is : %f n", Math.
asin(0.5));
System.out.printf("Arc tangent at argument 1.5 is : %f n", Math.
atan(1.5));
9 }
}
✆
✞
Arc cosine at argument 0.5 is : 1.047198
Arc sine at argument 0.5 is : 0.523599
Arc tangent at argument 1.5 is : 0.982794
✆

cosh, sinh & tanh
The cosh(), sinh() and tanh() functions compute the hyperbolic cosine, the
hyperbolic sine and the hyperbolic tangent of the argument respectively.
✞
1 double cosh(double x);
double sinh(double x);
3 double tanh(double x);
✆
A simple example is
✞
1 package jscript;
System.out.printf("Hyperbolic cosine of 0.5 is : %f n", Math.
cosh(0.5));
7 System.out.printf("Hyperbolic sine of 0.5 is : %f n", Math.sinh
(0.5));
System.out.printf("Hyperbolic tangent of 1.5 is : %f n", Math.
tanh(1.5));
9 }
}
✆
✞
Hyperbolic cosine at argument 0.5 is : 1.127626
Hyperbolic sine at argument 0.5 is : 0.521095
Hyperbolic tangent at argument 1.5 is : 0.905148
✆
1.6.2 Logarithm Function
exp, log
exp() represents the exponential of a value x with base ‘e’. log() represents the
logarithm of a value in natural base ‘e’.
✞
1 double exp(double x);
double log(double x);
✆
A simple example is
✞
package jscript;
2
4
6 System.out.printf("Exponential of 0.5 is : %f n", Math.exp(0.5))
;
System.out.printf("logarithm of 0.5 at base 10 is : %f n", Math.
log(0.5));

1.6. MATHEMATICAL OPERATOR 43
8 }
}
✆
✞
Exponential of 0.5 is : 1.648721
logarithm of 0.5 at base 10 is : -0.693147
✆
1.6.3 Arithmatic Function
pow, sqrt, floor, ceil & round
pow() makes second variable in power over the first variable. sqrt returns the
square root of a variable value. floor() rounded fraction to down. ceil() rounded
fraction to up and round() rounded up the number if fraction is equal or more
than 0.5.
✞
double pow(double x, double y);
2 double sqrt(double x);
double floor(double x);
4 double ceil(double x);
double round(double x);
✆
A simple example is
✞
1 package jscript;
System.out.printf("Power of 2 on base 3 is : %f n", Math.pow(3,
2));
7 System.out.printf("Square root of 1.45 is : %f n", Math.sqrt
(1.45));
System.out.printf("Ceiling of 1.45 is : %f n", Math.ceil(1.45));
9 System.out.printf("Flooring of 1.4855 is : %f n", Math.floor
(1.4855));
System.out.printf("Rounding of 6.157 is : %d n", Math.round
(6.157));
11 }
}
✆
✞
Power of 2 on base 3 is : 9.000000
Square root of 1.45 is : 1.204159
Ceiling of 1.45 is : 2.000000
Flooring of 1.4855 is : 1.000000
Rounding of 6.157 is : 6
✆

Chapter 2
String & Arrays
2.1 Strings
The string constant “x” is not the same as the character constant i.e. ‘x’. One
difference is that ‘x’ is a basic type (charcode), but “x” is a derived type, an
array of char. A String class type deals specifically with sequences of character
data. A string is declared and intialized as
✞
1 /*Declaration of string*/
String s=new String();
3 /*Initialization of string*/
char chars[] = { ’a’, ’b’, ’c’, ’d’, ’e’ };
5 String s = new String(chars);
✆
A substring can also be intialized if String class is used like
✞
1 char chars[] = { ’a’, ’b’, ’c’, ’d’, ’e’ };
String s = new String(chars, <pos index>, <number of chars>);
✆
In String objects length() method returns the number of characters in the string.
✞
String s = new String();
2 int n=s.length();/*Length of string.*/
✆
Characters are indexed from 0 to length()-1, and can be accessed with the
✞
charAt(<index>)
✆
method. String objects are read-only.
✞
1 char ch;
ch = "abcdedf".charAt(1);/*character at index 1.*/
✆
45

46 CHAPTER 2. STRING & ARRAYS
2.2 Array
Arrays in Java stores data in a single variable name with an index, also known
as a subscript. It is simply a list or ordered grouping for variables of the same
type. Arrays often help a programmer in organize collections of data efficiently
and intuitively.
Declaring an Array In Java an array is declared by using keyword new like
✞
int[] ia = new int[3];
2 float[] ia = new float[3];
String[] sa=new String[10];
✆
Initialization an Array In java, an array can be initialized at the time of
declaration or later the time. Synopsis for the initialization of an array during
the time of declaration is
✞
1 int[] ia = new int[3]{1, 2, 3};
✆
✞
1 package jscript;
5 int[] ia = new int[]{1, 2, 3};
System.out.println(ia.length);
7 }
}
✆
✞
3
✆
Dynamic Array Size If the array is declared as shown below then size of
array is determined at the execution time.
✞
1 int[] ia=new int[/*No value here*/];
✆
✞
1 package jscript;
5 int[] ia = new int[/*No value here*/]{1, 2, 3, 1, 2, 3};
System.out.println(ia.length);
7 }
}
✆
✞
6
✆

2.2. ARRAY 47
2.2.1 Dyanmic Array
2.2.2 Uni-dimensional Array
Arrays are declared and initialized like
✞
1 int numbers[6]; // array declared
int point[6]={0,0,1,0,0,0}; // array initialized
✆
The square brackets [] identify ‘numbers’ or ‘points’ and the rest as arrays,
and the number enclosed in the brackets indicates the number of elements in
the array. An element of the array can be accessed by its index number. In
following example, each element of the array is accessed by its index number.
✞
package jscript;
2
4
6 int i = 0;
int[] anArray = new int[4];
8 while (i < 4) {
anArray[i] = i;
10 System.out.println(anArray[i]);
i++;
12 }
}
14 }
✆
✞
0
1
2
3
✆
In the above example, the size of the array was not explicitly specified. The
compiler knows the size of array from the initialized list. The size of ‘anArray’
is ‘4’ because ‘anArray’ has four elements. Addition of an additional element
to the list will increase its size to five. Static declaration of the size of an array,
the array list will be overflow. To overcome this problem array is declared with
dynamic size.
2.2.3 Multi-dimensional Array
A multi-dimensional array can be declared as the synopsis given below.
✞
int[][] ia = new int[2][3];
2 /*OR*/
int[][] ia = new int[][]{{5, 2, 1},
4 {6, 7, 8}};
/*OR*/

6 int ia[][][] = new int[3][4][5];
✆
Where [2] represents to the number of rows and [3] represents to the number of
columns of the two dimensional array. Multi-dimensional array can be used to
add, subtract and product (either dot or cross) of two vectors or matrices.
✞
package jscript;
2
4
6 int ix, iy;
8 int[][] anArray = new int[5][5];
for (ix = 0; ix < 5; ++ix) {
10 for (iy = 0; iy < 5; ++iy) {
anArray[ix][iy] = ix * iy;
12 };
}
14 for (ix = 0; ix < 5; ++ix) {
for (iy = 0; iy < 5; ++iy) {
16 System.out.printf("%2dt", anArray[ix][iy]);
};
}
20 }
}
✆
✞
0 0 0 0 0
0 1 2 3 4
0 2 4 6 8
0 3 6 9 12
0 4 8 12 16
✆
2.2.4 Size of Array
In Java, size of array is obtained by using length object.
✞
1 package jscript;
int i = 0;
7 int[] anArray = new int[4];
System.out.println(anArray.length);
9 }
}
✆

2.3. CLASS, OBJECT & FUNCTION 49
✞
4
✆
2.3 Class, Object & Function
Like struct in C, java has classes and objects. Every object has a class that
defines its data and behavior. A class has (i) fields which are data variables
associated with a class and its objects. They stores results. (ii) Methods are
build from expressions and contain the executable code of a class. A public class
should be declared in a separate file having name as public class name. A class
is declared as
✞
1 class <class name>{
<scope> <data type> <var a>, <var b>;
3 }
✆
In following lines, class Trees is declared with two variables or fields.
✞
1 class Trees{
public char name;
3 public double length;
}
✆
Objects are created by expressions containing the new keyword. Creating an
object from a class definition is also known as instantiation; thus, objects are
often called instances.
✞
Trees t=new Trees();
✆
The members may be assigned a value as
✞
1 t.name="a";
✆
Again, the value of a class member can also be accessed by using
✞
1 t.name
/*or*/
3 t.length
✆
See example below:
✞
1 package jscript;
3 class Trees {
5 public char name;
public double length;
7 }

Trees t = new Trees();
13 t.name = 120;
t.length = 2;
15 System.out.println("Name of tree is " + t.name);
System.out.println("Length of tree is " + t.length);
17 }
}
✆
✞
Name of tree is x
Length of tree is 2.0
✆
A class can also have a return value to the caller by object method.
✞
package jscript;
2
class Box {
4
int length;
6 int width;
int height;
8
int Volume() {
10 return length * width * height;
}
12 }
Box b = new Box();
18 b.length = 2;
b.width = 1;
20 b.height = 3;
int vol = b.Volume();
22 System.out.printf("Volume of Box is %dn", vol);
}
24 }
✆
✞
Volume of Box is 6
✆
✞
1 package jscript;
/*Class*/
3
class myClass {
5
private String name;
7 private int age;

/*Object of the class and its initialization*/
9
public myClass(String name, int age) {
11 this.name = name;
this.age = age;
13 }
/*Object get name*/
15
public String getName() {
17 return name;
}
19 /*Object get age*/
21 public Object getAge() {
return age;
23 }
}
25
27
29 myClass sun = new myClass("Sooraj", 15);
System.out.printf("Name of person is %s.n", sun.getName());
31 System.out.printf("Name of person is %s.n", sun.getAge());
}
33 }
✆
✞
Name of person is Sooraj.
Name of person is 15.
✆
A class can also be accessed with arguments as shown in example below.
✞
package jscript;
2
class myClass {
4
public String name;
6 public int dis;
8 public myClass(String n, int d) {
name = n;
10 dis = d;
}
12 }
myClass sun = new myClass("Sooraj", 15);
18 System.out.printf("Distance of %s is %d.n", sun.name, sun.dis);

}
20 }
✆
✞
Distance of Sooraj is 15.
✆
Function in Java a group of statements and expressions which accepts inputs,
analyse them according to the statements and expressions and return the result.
There are no global functions in Java. The equivalent is to define static methods
in a class. Function overloading is allowed in java.
✞
1 public class <class name>{
public static <data type> <function name>(argument a, argument b) {
3 <expression>
}
5 }
✆
A function can be called by calling class name and envoking function name like
✞
1 <class name>.<function name>(argument a, argument b);
✆
Here, class name is the name of java file in which function is written. In the
following example, two files, Jscript.java and Sum.java are placed inside the
package jscript. The file containing main class is Jscrip.java and it contains the
codes given below.
✞
1 package jscript;
System.out.println("Sum of 2 and 3 is " + Sum.sum(2, 3));
7 }
}
✆
While the file containing Sum class and sum function is Sum.java and it contains
the codes given below.
✞
package jscript;
2
public class Sum {
4
public static int sum(int a, int b) {
6 return a + b;
}
8 }
✆
We call the sum function from main class as
✞
Sum.sum(2, 3)
✆
and the result given by program is

✞
Sum of 2 and 3 is 5
✆
2.3.1 Arguments
A functions accepts inputs through its arguments. A function with two argu-
ments is defined as
✞
1 public static int sum(int a, int b);
✆
Here, int a, int b are known as formal arguments. During the defining of a
function, each argument must be identified by its type. For example, to supply
two integer arguments to a function, it shall be defined like
✞
1 public static int sum(int a, int b);
✆
while, the definition of function as given below is illegal.
✞
1 public static int sum(int a, b);//Illegal definition
✆
Here, second argument ‘b’ is type unidentified. In Java, a function can be called
from anywhere by supplying actual arguments as
✞
1 Sum.sum(2, 3);
✆
See example below. Jscript.java contains the codes given below.
✞
1 package jscript;
System.out.println("Sum of 2 and 3 is " + Sum.sum(2, 3));
7 }
}
✆
Sum.java contains the codes given below.
✞
package jscript;
2
public class Sum {
4
public static int sum(int a, int b) {
6 return a + b;
}
8 }
✆
We call the sum function from the main class as
✞
Sum.sum(2, 3)
✆
and the result given by program is

✞
Sum of 2 and 3 is 5
✆
2.3.2 Prototyping
Function prototype allows to omit the variable name in its arguments. The legal
function prototyping are
✞
1 public static int sum(int, int); /*Illegal prototype.*/
public static int sum(int a, int b); /*Legal prototype.*/
3 public static int sum(a, int b); /*Illegal prototype.*/
✆
2.3.3 this Reference
The this reference is most commonly used as a way to pass a reference to the
current object as an argument to other methods or when the name of the field
are needed to access is hidden by a local variable or parameter declaration.
✞
1 package jscript;
3 class myClass {
5 public String name;/*Name field*/
public int dis; /*Distance field*/
7 /*Passed argument names are similar to field name.*/
public myClass(String name, int dis) {
9 /*To distict the field name from *
*argument this reference is used.*/
11 this.name = name;
this.dis = dis;
13 }
}
15
17
System.out.printf("Distance of %s is %d.n", sun.name, sun.dis);
21 }
}
✆
✞
Distance of Sooraj is 15.
✆
If this reference is not used then code and result shall be looked like
✞
1 package jscript;
3 class myClass {

5 public String name;/*Name field*/
public int dis; /*Distance field*/
7 /*Passed argument names are similar to field name.*/
public myClass(String name, int dis) {
9 /*To distict the field name from argument *
*this reference is used. Here no reference*
11 *is used so that the field parameter does *
*not store the values of name and distance*/
13 name = name;
dis = dis;
15 }
}
17
19
System.out.printf("Distance of %s is %d.n", sun.name, sun.dis);
23 }
}
✆
✞
Distance of null is 0.
✆
2.3.4 Field Declaration
A field can be declared as either annotations, access, static, final, transient or
volatile. A field cannot be both final and volatile. A static field is shared only
one instance by all objects of a class. A final variable is one whose value cannot
be changed after it has been initialized.
2.3.5 Inheritance
To inherit a class, one class is incorporate and defined in another class by using
the extends keyword.
✞
1 package jscript;
/*Creatign a super class*/
3 class BoxVol {
int l, w, h;
5 int Volume() {
return l * w * h;
7 }
}
9 /*Creating subclass extending to super class.*
*Here the variables and members of super are*
11 *accessed by object created for sub class. */
class BoxSur extends BoxVol {

13 int Surface() {
return 2 * (l * w + w * h + l * h);
15 }
}
19 /*Object cerated for box surface.*
*The scope of BoxSur is extende *
21 *to the BoxVol, hence variables *
*and all members of BoxVol are *
23 *accessible from created object.*/
BoxSur a = new BoxSur();
25 /*Access varibles of super class.*/
a.l = 2;
27 a.w = 1;
a.h = 3;
29 /*Fetch the member value of super class.*/
int vol = a.Volume();
31 System.out.printf("Volume of Box is %dn", vol);
/*Fetch the member value of sub class.*/
33 int sur = a.Surface();
System.out.printf("Surface Area of Box is %dn", sur);
35 }
}
✆
✞
Volume of Box is 6
Surface Area of Box is 22
✆
2.3.6 Function
In Java a function is defined as in language C. The return value of a function
may be integer, double, float, boolean or void type. A function is defined inside
the class as subclass. The synopsis of the function is
✞
int MyFunc(){
2 <expression>
}
✆
In following example, when a function is called it reset the value of ‘s’. And the
global value of ‘s’ is printed in output stream.
✞
1 package jscript;
/*To use s as global, it should be defined as static.*/
5 static double s = 0.0;
7 double MyFunc() {
s = 10;

2.4. THREADING 57
9 return s;
}
11
public static void main(String args[]) {
13
Jscript j = new Jscript();
15 j.MyFunc();
System.out.printf("s is %fn", s);
17 }
}
✆
✞
s is 10.000000
✆
2.3.7 Type of Objects
2.4 Threading
A thread is initiated by Thread object like
✞
1 Thread th = new Thread();
✆
In following example a thread is created.
✞
1 package jscript;
Thread th = new Thread();
7 System.out.println(th);
}
9 }
✆
✞
Thread[Thread-0,5,main]
✆
In following example,Jscript class is extended to Thread object.
✞
1 package jscript;
/*Class extended to Thread*/
3 public class Jscript extends Thread {
5 public static void main(String[] args) throws InterruptedException {
int i = 1;
7 for (;;) {
/*sleep method throws InterruptedException.*/
9 Thread.sleep(1000);
System.out.printf("Seconds passed %dn", i);
11 i++;

}
13 }
}
✆
✞
Seconds passed 1
Seconds passed 2
........
........
✆
Above example is rewritten and a new thread is initiated by using Thread object.
✞
package jscript;
2
4
public static void main(String[] args) throws InterruptedException {
6 int i = 1;
/*Independent Thread is initiated.*/
for (;;) {
10 /*sleep method throws InterruptedException.*/
th.sleep(1000);
12 System.out.printf("Seconds passed %dn", i);
i++;
14 }
}
16 }
✆
✞
Seconds passed 1
Seconds passed 2
........
........
✆
After a Thread object is created, it can be configured and run. A thread is
invoked by start() method. The virtual machine invokes the new thread’s run()
method, making the thread active. A thread can be invoked only once. Multiple
invoking of same thread results IllegalThreadStateException.
✞
package jscript;
2
4
public static void main(String[] args){
System.out.printf("Invoking same thread multiple times.n");
8 /*Multiple involke throws IllegalThreadStateException.*/
th.start();
10 th.start();
}
12 }
✆

2.4. THREADING 59
While a thread is running we can interact with it in other ways. After activating
the thread, we need to perform some action. The Runnable interface declares a
single method:
✞
public void run();
✆
Actually the code inside the run() object does the real job.
✞
1 package jscript;
5 private String word;
private int delay;
7
public Jscript(String w, int d) {
9 word = w;
delay = d;
11 }
13 @Override
public void run() {
15 try {
for (;;) {
17 System.out.printf(word + " n");
Thread.sleep(delay);
19 }
} catch (InterruptedException e) {
21 return;
}
23 }
new Jscript("ping", 1000).start();
27 new Jscript("PONG", 3000).start();
}
29 }
✆
✞
ping
PONG
ping
ping
PONG
✆
wait(), notify() and notifyAll() methods tells waiting threads that something
has occurred that might satisfy that condition. The wait() and notification
methods are defined in class Object and are inherited by all classes.
Name of thread can be changes by setName() method. See the example
below.

✞
1 package jscript;
5 @Override
public void run() {
7 System.out.println("Running....");
}
9
11 Jscript th1 = new Jscript();
Jscript th2 = new Jscript();
13 System.out.println("Name of first thread is :" + th1.getName());
System.out.println("Name of second thread is :" + th2.getName());
15
th1.start();
17 th2.start();
/*Change the name of first thread.*/
19 th1.setName("Konark");
System.out.println("After changing name of first thread:" + th1.
getName());
21 /*Change the name of second thread.*/
th1.setName("Khajuraho");
23 System.out.println("After changing name of second thread :" + th1
.getName());
}
25 }
✆
✞
Name of first thread is :Thread-0
Name of second thread is :Thread-1
After changing name of first thread:Konark
After changing name of second thread :Khajuraho
Running....
Running....
✆
Priority of a thread is set by using setPriority() method. There are three types
of priorities - MIN PRIORITY, NORM PRIORITY and MAX PRIORITY.
✞
package jscript;
2
public class Jscript extends Thread {
4
@Override
6 public void run() {
/*Current thread tells the current running thread*/
8 System.out.println(Thread.currentThread().getPriority());
}
10

2.4. THREADING 61
14 System.out.println("Name of first thread is :" + th1.getName());
System.out.println("Name of second thread is :" + th2.getName());
16 /*Change the name of first thread.*/
th1.setName("Konark");
18 th1.setPriority(MIN_PRIORITY);
System.out.println("After changing name of first thread:" + th1.
getName());
20 /*Change the name of second thread.*/
th1.setName("Khajuraho");
22 th1.setPriority(MAX_PRIORITY);
System.out.println("After changing name of second thread :" + th1
.getName());
24 th1.start();
th2.start();
26 }
}
✆
✞
Name of first thread is :Thread-0
Name of second thread is :Thread-1
After changing name of first thread:Konark
After changing name of second thread :Khajuraho
10
5
✆
A running thread is joined by using join() method.
✞
package jscript;
2
public class Jscript extends Thread {
4
public void run() {
6 System.out.println("Running..");
}
8
th1.start();
14 try {
th1.join();
16 } catch (Exception e) {
System.out.println(e);
18 }
th2.start();
20 th3.start();
}
22 }
✆

✞
Running..
Running..
Running..
✆
2.4.1 Exception Handling
In Java, when compiler encounters with errors it throws an exceptions. To run
the program, these errors must be caught by the invoking code. This invoking
code can handle the exception as needed and then continue executing. Uncaught
exceptions result in the termination of the thread of execution. Uncaught excep-
tions are reported by compiler. Exception objects are the Exception class, which
provides a string field to describe the error. All exceptions must be subclasses
of the class Throwable, which is the superclass of Exception. try-catch-finally
sequence is used to catch an Exception.
✞
1 package jscript;
int i = 1;
for (;;) {
9 try {/*Try to invoke thread by start method.*/
try {/*Try to invoke sleep thread.*/
11 th.sleep(2000);
}/*If any internal error occured *
13 *then catch the exception handle.*/
catch (InterruptedException ex) {
15 System.out.println("Sleep Interrupt Exception.");
}
17 th.start();
th.start();
19 } /*If any internal state error occured*
* then catch the exception handle. */
21 catch (IllegalThreadStateException ex) {
System.out.println("Illegal Thread State Exception.");
23 }
}
25 }
}
✆
✞
Illegal Thread State Exception.
Illegal Thread State Exception.
............
............
✆

Chapter 3
Accessing System Files
Standard Input-Output and access of files is a main part of computer program-
ming. In this chapter we shall discuss the importance and methodology of
accessing system and user define files.
3.1 Input Output
A Java program under execution opens automatically input and output streams.
The first standard stream is used for input buffering and the other used for
outputs. These streams are sequences of bytes. To read a character from a
BufferedReader, read() is used. Each time that read() is called, it reads a
character from the input stream and returns it as an integer value. It returns
-1 when the end of the stream is encountered.
✞
package jscript;
2 import java.io.*;
4 public static void main(String[] args) throws IOException {
char c;
6 BufferedReader br = new BufferedReader(new InputStreamReader(
System.in));
System.out.println("Enter characters, ’q’ to quit.");
8 do {
c = (char) br.read();
10 System.out.println(c);
} while (c != ’q’);
12 }
}
✆
To read a line from input console, readLine() is used as shown in example below.
✞
1 package jscript;
import java.io.*;
63

64 CHAPTER 3. ACCESSING SYSTEM FILES
BufferedReader br = new BufferedReader(new InputStreamReader(
System.in));
7 String str;
System.out.println("Enter contents in each line.");
9 System.out.println("Enter ’stop’ to quit.");
do {
11 str = br.readLine();
System.out.println(str);
13 } while (!str.equals("stop"));
}
15 }
✆
Buffer space is created by the allocate() method at ByteBuffer class. To create
one megabyte buffer space, allocate() method is used as
✞
1 ByteBuffer buff = ByteBuffer.allocate(1024 * 1024);
✆
This method is in nio.* class.
✞
1 package jscript;
3 import java.nio.*;
ByteBuffer buff = ByteBuffer.allocate(1024 * 1024);
9 System.out.println(buff);
}
11 }
✆
✞
java.nio.HeapByteBuffer[pos=0 lim=1048576 cap=1048576]
✆
The read() method is used to place read data into buffer by using as
✞
1 inf.read(buff);
✆
If there is requirement to write data in ‘buff’ in out stream it must be converted
into write mode by using flip() method.
✞
1 buff.flip();
outf.write(buff);
✆
Other buffer types are ShortBuffer, IntBuffer, CharBuffer, FloatBuffer, Double-
Buffer and LongBuffer.
3.1.1 File Handling
Some times it is required to read, write and access a file to read or write some
contents to it.

3.1. INPUT OUTPUT 65
Open a File
FileInputStream class is used to open a file as shown in the following syntax.
✞
FileInputStream(String <file name>) throws FileNotFoundException
✆
Here, ‘file name’ specifies the name of the file that needed to be open. If file
does not exist to open FileNotFoundException is thrown.
✞
1 import java.io.*;
int i;
5 FileInputStream fin;
try {
7 fin = new FileInputStream("test.txt");
} catch (FileNotFoundException e) {
9 System.out.println("File Not Found");
return;
11 }
fin.close();
13 }
}
✆
Again a new file can be created by using createNewFile() method. This method
first checks whether a named file is pre-exists or not. If exists, it does not
create new file with same name and returns false and throws an IOException.
If created then it returns true.
✞
package jscript;
2
import java.io.*;
4
6
public static void main(String[] args) throws IOException {
8 File f = new File("newfile.dat");
boolean success;
10 success = f.createNewFile();
if(success){
12 System.out.println("Created new file.");
}else{
14 System.out.println("Unable to create new file.");
}
16 }
}
✆
✞
Created new file.
✆

Close a File
Any opened file shall be closed when it is not required or required by other
program to access it. Opened file is closed by using
✞
1 fin.close();
✆
Reading File
The contents of the file are read by using object read(). It returns the character
code read from the file. read() returns ‘-1’ when it encounters EOF.
✞
1 package jscript;
3 import java.io.*;
7 int i;
FileInputStream fin;
9 try {
fin = new FileInputStream("test.txt");
11 } catch (FileNotFoundException e) {
System.out.println("File Not Found");
13 return;
}
15 do {
i = fin.read();
17 if (i != -1) {
System.out.print((char) i);
19 }
} while (i != -1);
21 fin.close();
}
23 }
✆
Writing File
FileOutputStream is used to create and write a file. The syntax for this class is
✞
1 FileOutputStream(String <file name>) throws FileNotFoundException
✆
Here, ‘file name’ specifies the name of the file that is to be created. If it is
unable to create a new file to write, FileNotFoundException is thrown. Any
pre-existing file is destroyed or overwritten. The contents are written to the file
by using write() method.
✞
1 package jscript;

3 import java.io.*;
int i = 0;
9 FileOutputStream fout;
try {
11 fout = new FileOutputStream("text.txt");
} catch (FileNotFoundException e) {
13 System.out.println("Unable to open a file");
return;
15 }
try {
17 do {
fout.write(i);
19 i++;
} while (i < 10);
21 } catch (IOException e) {
System.out.println("File Error");
23 }
fout.close();
25 }
}
✆
Temporary File
In Java, a temporary file is created by method createTempFile(). Compiler
throws errors if we try to create two temporary files with same name. To create
the temporary file in current temporary file, use following synopsis
✞
File <temp file name> = File.createTempFile(<name>, <ext>, cwd);
✆
✞
1 package jscript;
3 import java.io.*;
File temp = File.createTempFile("tmp", ".tmp");
9 System.out.println(temp);
}
11 }
✆
✞
C:DOCUME~1ADMINI~1LOCALS~1Temptmp1895285192040487408.tmp
✆
To create temporary file anywhere you want then use following synopsis.

✞
1 File loc = new File(<path>);
File <temp file name> = File.createTempFile(<name>, <ext>, loc);
✆
✞
package jscript;
2
import java.io.*;
4
6
8 File loc = new File("d:/");
File temp = File.createTempFile("temp", ".tmp", loc);
10 System.out.println(temp);
}
12 }
✆
✞
d:temp7521897237899708714.tmp
✆
Before creation of temporary file of specific size, the required space in the direc-
tory should be known. To get the size of destination, getTotalSpace() method
is used.
✞
1 package jscript;
3 import java.io.*;
7 public static void main(String[] args){
File d = new File("d:/");
9 long ds = d.getTotalSpace();
System.out.println("Size of root D:/ is " + ds + "bytes.");
11 File e = new File("e:/");
long es = e.getTotalSpace();
13 System.out.println("Size of root E:/ is " + es + "bytes.");
}
15 }
✆
✞
Size of root D:/ is 110637346816bytes.
Size of root E:/ is 117942775808bytes.
✆
Memory Mapped I/O
In the nio.* class, The MappedByteBuffer class maps a file directly into a Byte-
Buffer. It can be operatred by using put( ), get( ), putInt( ), getInt( ) and other
methods. put( ) and get( ) access the file directly without copying a lot of data
to and from RAM. The synopsis of it is

✞
MappedByteBuffer buff
2 = <file channel>.map(FileChannel.MapMode.<file mode>, <position>, <
size>);
✆
The ‘file mode’ operations are READ ONLY, READ WRITE and PRIVATE.
✞
package jscript;
2
import java.io.*;
4 import java.nio.*;
import java.nio.channels.*;
6
8
10 /*Open new file.*/
File file = new File("test.txt");
12 /*Get file stream.*/
FileInputStream fis = new FileInputStream(file);
14 /*Try to get the channel of the opened file stream.*/
try (FileChannel fc = fis.getChannel()) {
16 /*Get the size of file.*/
long size = fc.size();
18 /*Map the file data from the file channel.*/
MappedByteBuffer bb =
20 fc.map(FileChannel.MapMode.READ_ONLY, 0, size);
22 for (int i = 0; i < size; i++) {
try {
24 /*Do what you need the mapped data.*/
System.out.println(i+" -> "+bb.get(i));
26 } catch (Exception e) {
}
28 }
}
30 }
}
✆
MappedByteBuffer has three methods, force( ), load( ), and isLoaded( ). The
load( ) method attempts to load the entire buffer into main memory. If the
data is larger than Java’s heap size, this is likely to cause some page faults and
disk thrashing. The isLoaded( ) method tells whether a buffer is loaded. To put
data in a MappedByteBuffer, force( ) method is used.
Random Access File
In Java, normally a file stream is started accessing data from beginning. To
access the data of a file from a specific position, RandomAccessFile class is
used. The synopsis of it is

✞
1 RandomAccessFile rs=new RandomAccessFile(<file name>, <access mode>);
✆
In Java, there is no write only access mode, so read and write both mode are
used commonly. The getFilePointer( ) and seek( ) methods allow to query and
change the position in the file at which reads and writes occur.
✞
1 package jscript;
3 import java.io.*;
9 RandomAccessFile rf = new RandomAccessFile(file, "rw");
rf.seek(10);
11 long rfp1 = rf.getFilePointer();
System.out.println("Current position of file is " + rfp1);
13 rf.seek(0);
long rfp2 = rf.getFilePointer();
15 System.out.println("Current position of file is " + rfp2);
rf.close();
17 }
}
✆
✞
Current position of file is 10
✆
✞
skipBytes(<bytes number>)
✆
skipBytes() skips a file by ‘n’ bytes from the current position of the file. close()
method is used to close the current open file.
✞
1 package jscript;
3 import java.io.*;
9 RandomAccessFile rf = new RandomAccessFile(file, "rw");
rf.seek(10);
11 long rfp1 = rf.getFilePointer();
System.out.println("Current position of file is " + rfp1);
13 rf.skipBytes(10);
long rfp2 = rf.getFilePointer();
15 System.out.println("Current position of file is " + rfp2);
rf.close();

17 }
}
✆
✞
✆
File Pointer to Class
3.1.2 File Directory
Sometimes user needs to read, create, delete or change a directory. In this
section we will use specific functions related with handling of a directory.
Finding Roots
To get the system partitions, listRoots() method is used for listing of roots. This
method returns the array of all disk partitions, i.e. roots.
✞
package jscript;
2
import java.io.*;
6 /*Get the array of roots.*/
File[] roots = File.listRoots( );
8 /*Print all root names.*/
for (int i = 0; i < roots.length; i++) {
10 System.out.println(roots[i]);
}
12 }
}
✆
✞
C:
D:
E:
F:
H:
✆
File Object
File deals directly with files and the file system. The File class describes the
properties of a file itself. A File object is used to obtain or manipulate the
information associated with a disk file, such as the permissions, time, date, and
directory path, and to navigate subdirectory hierarchies. The syntax of File is
✞
1 File(<path or URI of file>);
✆

There are several objects which tell information about the file’s name, its path,
its size, is a file, is a directory, is readable, is writable, make directory etc. Few
of then are used in the following example for file “test.txt”.
✞
1 package jscript;
3 import java.io.File;
File f1 = new File("test.txt");
9 System.out.println(f1.getName());/*test.txt*/
System.out.println(f1.getPath());/*test.txt*/
11 System.out.println(f1.canRead());/*true*/
System.out.println(f1.canWrite());/*true*/
13 System.out.println(f1.exists());/*true*/
System.out.println(f1.isFile());/*true*/
15 System.out.println(f1.length());/*210 (in bytes)*/
}
17 }
✆
✞
test.txt
test.txt
true
true
true
true
210
✆
Directory
A directory is a File that contains a list of other files and directories. We can
create a File object and checked whether its is a directory or not by isDirectory()
method. Other files can be listed by using method list() on the object to extract
the list of other files and directories inside. Its synopsis is
✞
1 <file object>.list();
✆
The list of files is returned in an array of String objects.
✞
1 package jscript;
File f1 = new File("./");

9 if (f1.isDirectory()) {
String flist[] = f1.list();
11 for (int i = 0; i < flist.length; i++) {
System.out.println(flist[i]);
13 }
}
15 }
}
✆
✞
build
build.xml
manifest.mf
nbproject
src
test.txt
text.txt
✆
mkdir( ) method creates a directory, returning true on success and false on
failure. Failure indicates that the path specified in the File object already exists,
or that the directory cannot be created because the entire path does not exist
yet. To create a directory for which no path exists, use the mkdirs() method.
It creates both a directory and all the parents of the directory.
✞
1 package jscript;
File f1 = new File("ak");
9 boolean i = f1.mkdir();
System.out.println(i);
11 }
}
✆
A file or directory can be delete by delete() method. It returns true on successful
and false on failure. Failure indicates either file or directory does not exist.
✞
package jscript;
2
import java.io.File;
4
6
8 File f1 = new File("ak");
boolean i = f1.mkdir();
10 System.out.println(i);
}

12 }
✆
A file or directory can be rename by renameTo() method. It returns true on
successful and false on failure. Failure indicates either file or directory either
does not exist or can not be renamed.
✞
package jscript;
2
import java.io.File;
4
6
8 File f1 = new File("test.txt");
File f2 = new File("ab.txt");
10 f1.mkdir();
boolean i = f1.renameTo(f2);
12 System.out.println(i);
}
14 }
✆
3.2 JNI

Java Programming Notes for Beginners by Arun Umrao

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