Java is a programming language that is simple, object-oriented, and robust. It allows programs to be portable across platforms and provides automatic memory management through garbage collection. Key features of Java include its platform independence through bytecode, its object-oriented approach, networking capabilities, security features, performance through just-in-time compilation, and support for multithreading. Java code is compiled to bytecode that can run on any Java Virtual Machine, making programs highly portable.

1.  Java is a whole platform
 huge library
 lots of reusable code
 execution environment
 security,
 portability across operating systems,
 and automatic garbage collection.

2.  11 buzzwords:
 1. Simple
 2. Object-Oriented
 3. Network-Savvy
 4. Robust
 5. Secure
 6. Architecture-Neutral
 7. Portable
 8. Interpreted
 9. High-Performance
 10. Multithreaded
 11. Dynamic

3.  system can be programmed easily
 Java omits many rarely used, poorly understood,
confusing features of C++
 header files,
 pointer arithmetic (or even a pointer syntax),
 structures,
 unions,
 operator overloading,
 virtual base classes, and so on.
 If you know C++, you will find the transition to
the Java syntax easy.

4.  Another aspect of being simple is being
small.
 goals of Java is to enable the construction of
software that can run stand-alone in small
machines.
 The size of the basic interpreter and class
support is about 40K;
 the basic standard libraries and thread support
add another 175K.
 There is now a separate Java Micro Edition
with a smaller library, suitable for
embedded devices.

5.  focuses on the data and on the interfaces to
that object.
 Analogy : carpentry
 An “object-oriented” carpenter would be mostly
concerned with the chair he was building, and
secondarily with the tools used to make it;
 A “non-object-oriented” carpenter would think
primarily of his tools.
 The major difference between Java and C++
lies in multiple inheritance, which Java has
replaced with the simpler concept of interfaces.

6.  Java has an extensive library of routines for
coping with TCP/IP protocols like HTTP and
FTP.
 Java applications can open and access objects
across the Net via URLs with the same ease as
when accessing a local file system.
 networking capabilities of Java to be both strong
and easy to use, such as
 opening a socket connection
 remote method invocation mechanism

7.  Reliable
 early checking for possible problems,
 later dynamic (runtime) checking,
 and eliminating situations that are error-prone.
 Java has a pointer model
 that eliminates the possibility of
 overwriting memory
 and corrupting data.
 Java compiler detects many problems that, in
other languages, would show up only at
runtime.

8.  used in networked/distributed environments
 Java enables the construction of
 virus-free,
 tamper free systems.
 implementation of
 the virtual machine
 and the security libraries
 Java was designed to make certain kinds of
attacks impossible, among them:
 Overrunning the runtime stack—a common attack of
worms and viruses
 Corrupting memory outside its own process space
 Reading or writing files without permission

9.  architecture-neutral object file format
 the compiled code is executable on many
processors,
 given the presence of the Java runtime system.
 bytecode -> machine code
 a process called just-in-time compilation

10.  Unlike C and C++, there are no “implementation-
dependent” aspects of the specification.
 The sizes of the primitive data types are
specified.
 For example, an int in Java is always a 32-bit integer.
 The libraries that are a part of the system define
portable interfaces.
 For example, there is an abstract Window class and
implementations of it for
 UNIX,
 Windows,
 and the Macintosh.

11.  The Java interpreter can execute Java bytecodes
directly on any machine to which the interpreter
has been ported.
 Since linking is a more incremental and
lightweight process, the development process can
be much more rapid and exploratory.

12.  For example, a just-in-time compiler can monitor
which code is executed frequently and optimize
just that code for speed.
 A more sophisticated optimization is the
elimination(or “inlining”) of function calls.
 it can undo that optimization later if necessary

13.  benefits of multithreading are
 better interactive responsiveness
 and real-time behavior.
 Multithreading is easy in Java.
 advantage for multiprocessor systems.
 Java offloads the implementation of
multithreading to the underlying
 operating system
 or a thread library.

14.  Java is a more dynamic language than C or C++.
 designed to adapt to an evolving environment
 Libraries can freely add
 new methods
 and instance variables
 without any effect on their clients.
 In Java, finding out runtime type information is
straightforward.
 This is extremely useful for systems that need to
analyze objects at runtime,
 such as Java GUI builders,
 smart debuggers,
 pluggable components,
 and object databases.

15.  The idea here is simple: Users will download Java
bytecodes from the Internet and run them on
their own machines.
 Java programs that work on web pages are called
applets
 To use an applet, you only need a Java-enabled
web browser, which will execute the bytecodes
for you.
 Inserting an applet into a web page works much
like embedding an image. The applet becomes a
part of the page, and the text flows around the
space used for the applet

16.  Figure 1.1 shows a good example of a dynamic web page that
carries out sophisticated calculations.

17.  1991 group of Sun engineers, led by Patrick
Naughton and James Gosling
 wanted to design a small computer language
 used for consumer devices like cable TV switchboxes.
 The project was code-named “Green.”

18.  Java is an extension of HTML
 I use XML, so I don’t need Java.
 Java is an easy programming language to learn.
 Java will become a universal programming language for all
platforms.
 Java is just another programming language
 Now that C# is available, Java is obsolete.
 Java is proprietary, and it should therefore be avoided.
 Java is interpreted, so it is too slow for serious applications.
 All Java programs run inside a web page.
 Java programs are a major security risk.
 JavaScript is a simpler version of Java.
 With Java, I can replace my computer with a $500 “Internet
appliance.”

19. Output: We will not use 'Hello, World!'

20.  Java is case sensitive.
 Public -> access modifier;
 control the level of access
 class ->Everything in a Java program must be inside a
class.
 FirstSample -> name of the class
 Names must begin with a letter
 You cannot use a Java reserved word for a class name.
 The standard naming convention is that class names are
nouns that start with an uppercase letter and followed
by “camel case”.
 file name for the source code should be same the class
name.
 FirstSample.java
 The Java compiler automatically names the bytecode file
FirstSample.class and stores it in the same directory as the
source file.
 launch the program by issuing the following command:
 java FirstSample

21.  the Java virtual machine always starts execution
with the code in the main method in the class
 You can add your own methods to a class and call them
from the main method.
 In Java, as in C/C++, braces delineate the parts
(usually called blocks) in your program.
 In Java, the code for any method must be started by an
opening brace { and ended by a closing brace }.
 For now, don’t worry about the keywords “static
void”.

22.  In Java, every statement must end with a semicolon
 System.out object and calling its println method
 general syntax
 object.method(parameters)
 we are calling the println method and passing it a
string parameter.
 The method displays the string parameter on the
console.
 Methods can use zero, one, or more parameters
(some programmers call them arguments).

23.  Java has three ways of marking comments.
 1.The most common form is a //.
 You use this for a comment that will run from the // to the
end of the line.
 Eg:System.out.println("Hello, World!"); // is this too cute?
 2.longer comments , you can mark each line with a //,
or you can use the /* and */
 3./** to start and a */ to end
 Used in automatic documentation generation

24.  Java is a strongly typed language
 every variable must have a declared type
 There are eight primitive types in Java
 Four of them are integer types;
 two are floating-point number types;
 one is the character type char,
 used for code units in the Unicode encoding scheme
 and one is a boolean type
 for truth values.

25.  1.Integer Types
 The integer types are for numbers without fractional parts
 Negative values are allowed
 Long integer numbers have a suffix L (for example,
4000000000L).
 Hexadecimal numbers have a prefix 0x (for example,
0xCAFE).
 Octal numbers have a prefix 0. For example, 010 is 8.
 you can write numbers in binary, with a prefix 0b. For
example, 0b1001 is 9.

26.  2. Floating-Point Types
 The floating-point types denote numbers with fractional parts
 Numbers of type float have a suffix F (for example, 3.14F).
 Floating-point numbers without an F suffix (such as 3.14) are
considered to be of type double.
 You can optionally supply the D suffix (for example, 3.14D).
 there are three special floating-point values to denote
overflows and errors:
 • Positive infinity
 dividing a positive number by 0 is positive infinity
 • Negative infinity
 • NaN (not a number)
 Computing 0/0 or thesquare root of a negative number yields NaN.

27.  3. The char Type
 The char type is used to describe individual characters
Character constants
 Eg: 'A' is a character constant with value 65
Unicode code units can be expressed as
hexadecimal values from u0000 to uFFFF.
 Eg:u2122 for (™)
 Eg:u03C0 for pi (π).
The u escape sequence can even be used outside
quoted character constants and strings.
 For example,
public static void main(Stringu005Bu005D args)
 is perfectly legal—u005B and u005D are the encodings
for [ and ].

29.  4. The boolean Type
 two values,
 false
 true
 used for evaluating logical conditions
 cannot convert between integers and boolean values

30.  every variable has a type
 You declare a variable by placing the type first,
followed by the name of the variable.
 examples:
 double salary;
 int vacationDays;
 long earthPopulation;
 boolean done;
semicolon is necessary
 variable name must begin with a letter and must be a
sequence of letters or digits.
 Length of a variable name is unlimited.
 cannot use a Java reserved word for a variable name
 You can have multiple declarations on a single line:
 int i, j; // both are integers

31.  1. Initializing Variables
 First: declare a variable
 Second: initialize it by an assignment statement
 Example:
int vacationDays;
System.out.println(vacationDays); // ERROR--variable not
initialized
 Correct way:
int vacationDays;
vacationDays = 12;
 You can both declare and initialize a variable on the
same line.
 For example:int vacationDays = 12;

32.  2. Constants
 keyword final to denote a constant
 The keyword final indicates that you can assign to the
variable once, and then its value is set once and for
all.
 class constants

33.  arithmetic operators +, -, *, /
 Integer remainder (sometimes called modulus) is
denoted by %.
 example, 15 / 2 is 7, 15 % 2 is 1, and 15.0 / 2 is 7.5
 Note:
 integer division by 0 raises an exception,
 whereas floating-point division by 0 yields an infinite or NaN
result.
 x += 4; is equivalent to x = x + 4;

34.  1. Increment and Decrement Operators
 n++ adds 1 to the current value of the variable n, and
n-- subtracts 1 from it.
 For example,
the code int n = 12;
n++;
changes n to 13.
 operators change the value of a variable,
 they cannot be applied to numbers themselves.
 For example, 4++ is not a legal statement.

35.  2. Relational and boolean Operators
Equality
 double equal sign, ==.
 For example, the value of 3 == 7 is false.
Use a != for inequality.
 For example, the value of 3 != 7 is true.
< (less than),
> (greater than),
<= (less than or equal),
and >= (greater than or equal) operators
&& for the logical “and” operator and || for the
logical “or” operator.
exclamation point ! is the logical negation operator
The && and || operators are evaluated in “short
circuit” fashion

36.  expression1 && expression2
 and the truth value of the first expression has been
determined to be false, then it is impossible for the result to
be true.
 expression1 || expression2
 is automatically true if the first expression is true, without
evaluating the second expression.
 ternary ?: operator
 condition ? expression1 : expression2
evaluates to the first expression if the condition is true, to
the second expression otherwise

37.  3. Bitwise Operators
 The bitwise operators are
 & (“and”) | (“or”) ^ (“xor”) ~ (“not”)

38.  4. Mathematical Functions and Constants
 Math class contains the mathematical functions
 raising a quantity to a power
 double y = Math.pow(x, a);
 sets y to be x raised to the power a
 trigonometric functions
 Math.sin
 Math.cos
 Math.tan
 Math.atan
 Math.atan2

39.  exponential function with its inverse, the natural
logarithm, as well as the decimal logarithm:
 Math.exp
 Math.log
 Math.log10
 the two mathematical constants π and e:
 Math.PI
 Math.E

40.  5. Conversions between Numeric Types

41.  six solid arrows in Figure 3.1 denote conversions
without information loss
 The three dotted arrows denote conversions that may
lose precision
 When two values are combined with a binary operator
(such as n + f where n is an integer and f is a floating-
point value), both operands are converted to a common
type before the operation is carried out.
 • If either of the operands is of type double, the other one
will be converted to a double.
 • Otherwise, if either of the operands is of type float, the
other one will be converted to a float.
 • Otherwise, if either of the operands is of type long, the
other one will be converted to a long.
 • Otherwise, both operands will be converted to an int.

42.  6. Casts
 you saw that int values are automatically converted to
double
 On the other hand, when you want to consider a double
as an integer
 Conversions in which loss of information is possible are done
by means of casts
 The syntax for casting is to give the target type in
parentheses, followed by the variable name.
 For example:
double x = 9.997;
int nx = (int) x;
 If you want to round a floating-point number to the
nearest integer use the Math.round method:
double x = 9.997;
int nx = (int) Math.round(x);

43.  7. Parentheses and Operator Hierarchy
 Table 3.4 on the following page shows the
precedence of operators.
 If no parentheses are used, operations are
performed in the hierarchical order indicated.
 For example, && has a higher precedence than ||,
so the expression
 a && b || c

45.  8. Enumerated Types
 Sometimes, a variable should only hold a restricted set
of values.
 For example, you may sell clothes or pizza in four sizes:
small, medium, large, and extra large.
 Of course, you could encode these sizes as integers 1,
2, 3, 4, or characters S, M, L, and X. But that is an
error-prone setup. It is too easy for a variable to hold a
wrong value (such as 0 or m).
 You can define your own enumerated type whenever
such a situation arises. An enumerated type has a finite
number of named values.
 For example:
 enum Size { SMALL, MEDIUM, LARGE, EXTRA_LARGE };
Now you can declare variables of this type:
 Size s = Size.MEDIUM;

50.  accept input and properly format the program
output
 console for input and output

51.  1. Reading Input
 “standard input stream” System.in isn’t simple
 first construct a Scanner that is attached to System.in:
Scanner in = new Scanner(System.in);
 various methods of the Scanner class to read input.
For example,
The nextLine method reads a line of input.
System.out.print("What is your name? ");
String name = in.nextLine();
Here, we use the nextLine method because the input might
contain spaces.
 To read a single word (delimited by whitespace), call
String firstName = in.next();
 To read an integer, use the nextInt method.
System.out.print("How old are you? ");
int age = in.nextInt();
 Similarly, the nextDouble method reads the next
floating-point number.

53.  OUTPUT:
Hello, Cay. Next year, you'll be 52
 import java.util.*;
 at the beginning of the program. The Scanner class is defined
in the java.util package.
 Whenever you use a class that is not defined in the basic
java.lang package, you need to use an import directive.

54.  The Scanner class is not suitable for reading a
password from a console since the input is plainly
visible to anyone.
 Java SE 6 introduces a Console class specifically for this
purpose.
 To read a password, use the following code:
 For security reasons, the password is returned in an array of
characters rather than a string.

56.  2. Formatting Output
double x = 10000.0 / 3.0;
System.out.print(x);
Prints:
3333.3333333333335
 formatting numbers
System.out.printf("%8.2f", x);
 prints x with a field width of 8 characters and a
precision of 2 characters.
3333.33
 System.out.printf("Hello, %s. Next year, you'll be %d",
name, age);
Each of the format specifiers that start with a % character is
replaced with the corresponding argument.

58.  you can specify flags that control the appearance of
the formatted output
 System.out.printf("%,.2f", 10000.0 / 3.0);
Prints:
3,333.33

59.  You can use the static String.format method to create
a formatted string without printing it:
String message = String.format("Hello, %s. Next year, you'll be
%d", name, age);
 date and time formatting options of the printf method.
Use a two letter format, starting with t and ending in
one of the letters of Table 3.7;
System.out.printf("%tc", new Date());
prints the current date and time in the format
Mon Feb 09 18:05:19 PST 2004

62.  3. File Input and Output
 To read from a file, construct a Scanner object like
this:
 Scanner in = new Scanner(Paths.get("myfile.txt"));
 If the file name contains backslashes, remember to escape
each of them with an additional
 backslash: "c:mydirectorymyfile.txt".
 To write to a file, construct a PrintWriter object. In
the constructor, simply supply the file name:
 PrintWriter out = new PrintWriter("myfile.txt");

64.  Control Flow
 conditional statements
 loops

65.  1. Block Scope
 A block or compound statement is any number of simple
Java statements surrounded by a pair of brace
 Blocks define the scope of your variables.
 A block can be nested inside another block.
 public static void main(String[] args)
 {
int n;
. . .
{
int k;
. . .
} // k is only defined up to here
}

66.  public static void main(String[] args)
{
int n;
. . .
{
int k;
int n; // ERROR--can't redefine n in inner block
. . .
}
}

67.  2. Conditional Statements
 if (condition) statement
 condition must be surrounded by parentheses
 multiple statements, use a block statement that takes
the form

68.  if (condition) statement1 else statement2

70. 3. Loops
 The while loop executes a statement (which may be a
block statement) while a condition is true.
 The general form is while (condition) statement

71.  do statement while (condition);

72.  4. Determinate Loops
 iteration controlled by a
 counter
 similar variable that is updated after every iteration

73.  5. Multiple Selections—The switch Statement

74.  6. Statements That Break Control Flow
 break statement
 exit a switch
 break out of a loop

75.  java.math package:
 BigInteger
 BigDecimal
 These are classes for manipulating numbers with an
arbitrarily long sequence of digits.
 The BigInteger class implements arbitrary-precision
integer arithmetic
 BigDecimal does the same for floating-point numbers.
 Unfortunately, you cannot use the familiar
mathematical operators such as + and * to combine big
numbers.

78.  An array is a data structure that stores a collection of values
of the same type.
 You access each individual value through an integer index.
 For example, if a is an array of integers, then a[i] is the ith
integer in the array.
 declaration of an array a of integers:
int[] a;
 Use the new operator to create the array.
int[] a = new int[100];
 fill the elements in an array

79.  1. The “for each” Loop
 The enhanced for loop
for (variable : collection) statement
 For example,
for (int element : a)
System.out.println(element);
prints each element of the array a on a separate line.
You should read this loop as “for each element in a”.
 The traditional for loop
for (int i = 0; i < a.length; i++)
System.out.println(a[i]);

80.  2. Array Initializers and Anonymous Arrays
 int[] smallPrimes = { 2, 3, 5, 7, 11, 13 };
 Notice that you do not call new when you use this syntax.
 You can even initialize an anonymous array:
 new int[] { 17, 19, 23, 29, 31, 37 }
 This expression allocates a new array and fills it with the
values inside the braces.

81.  3. Array Copying
 You can copy one array variable into another, but then
both variables refer to the same array:
 If you want to copy all values of one array into a new
array, you use the copyOf method in the Arrays class:

82.  4. Command-Line Parameters
 Every Java program has a main method with a String[]
args parameter.
 public static void main(String[] args)

83.  5. Array Sorting
 To sort an array of numbers, you can use one of the
sort methods in the Arrays class:
int[] a = new int[10000];
. . .
Arrays.sort(a)
This method uses the QuickSort algorithm

84.  6. Multidimensional Arrays
 It uses more than one index to access array
elements
used for tables and other more complex
arrangements
 two-dimensional array (matrix)
 double[][] balances;

85.  7. Ragged Arrays
 Java has no multidimensional arrays
 Multidimensional arrays are faked as “arrays of
arrays.”
 balances[i][j]