chap4.pptx ffdddfdfdfddddddffffffffffffff

Chapter 2
Elementary Programming

Simple Java Program
statement(s);
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807 MODIFIED BY: Abla Hussein

Java Reserved Keywords
 Reserved words, or keywords, have a specific
meaning to the compiler and cannot be used for
other purposes in the program. For example, when
the compiler sees the word class, it understands that
the word after class is the name for the class.
 public, static, void, main, String, void, print (Reserved words)

Java Reserved Keywords
-Reserved words, or keywords, have a specific meaning to the compiler
and cannot be used for other purposes in the program. For example, when
the compiler sees the word class, it understands that the word after class
is the name for the class.

Identifiers
- Identifiers are the names that identify the elements such as
classes, methods, and variables in a program.
1. An identifier cannot be a reserved word
2. An identifier must start with a letter, It cannot start with a
digit.
3. An identifier can not contain space or special characters
(Except an underscore (_), and $).
4. An identifier is a sequence of characters that consists of
letters, digits, underscores ( _ ), and dollar signs ($).
5. An identifier cannot be true, false, or null.
6. An identifier can be of any length.

Identifiers
 Examples
invalid identifier
Valid Identifiers
Identifiers
main
Main
AV$$M
_Aa
A B
3_AB
AB13

Identifiers
Invalid Identifier
Valid Identifier
cAr<class
cAr
public
My_naMe
My name
Hel$4
12new
T_12
false
_ST
new#
$nAME
?hello
public5
na(me
Class

Print Statement
-Print statement is used to display outputs on the console (output screen).
-Two forms of printing statement:
1. System.out.print( );
2. System.out.println( );
- Both statements are used to display the result on the console.
-In the System.out.print( ); the output of the next immediate print
statement will be printed on the same line.
-In the System.out.println( ); the output of the next immediate print
statement will be printed on a new line.
-In other words, the println( ) moves the cursor to a new line in the
console (output screen) after the printing execution.
-The print( ) keeps the cursor on the same line in the console after the
printing execution.

Print Statement
-Example 1:
The output will be as following:

Print Statement
Example 2:

Comments
-Comments help programmers to communicate, remember and
understand the program (give better understanding of the
program). They are not programming statements and thus are
ignored by the compiler.
-Two Types of Comments:
1. Single line comments: comments are preceded by double
forward slashes (//) on only one line.
2. Multiline comments: comments are enclosed between /* and
*/ on one or several lines.
-When the compiler sees //, it ignores all text after // on the
same line .
-When it sees /*, it scans for the next */ and ignores any text
between /* and */ .

Comments
Examples:
1. Line comment:
2. Multiline comment:
/* this program prints welcome to java!!! */
/* this program
prints welcome
to java!!! */
// This program prints welcome to java!!!

Comments
 Example 1
Example 2 :

Escape Characters
- Escape characters can be used in print statement, and it has
different forms.
- Escape characters are enclosed within “ ” or ‘ ’.
Meaning
Escape Character
Line feed
n
tab
t
Back slash

Single quote
’
Double quote
"

Escape Characters
Example 1
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807 MODIFIED BY: Abla
Hussein

Escape Characters
Example 2:

Escape Characters
- Example 3:

Data Types
Primitive Data types:
1. Numeric Data types: byte, short, int, long, float, double.
2. Character Data type.
3. Boolean Data type.
Non-primitive Data type:
1. String.

Variables
- A variable is a name for a location in memory, and used to store
a value of a certain datatype.
- A variable must be declared by specifying its name and the type
of information that it will hold (data type).
- The syntax for declaring a varaible is:
Example: int x;
double y;
int sum;
datatype varName;

Variables
- Multiple variables of the same data type can be declared in
one declaration, as following:
Example:
int x,y,z;
double m1,m2,m3,avg;
datatype varName1, varName2, … varNameN;

Variables
int x; // Declare x to be an
// integer variable;
double radius; // Declare radius to
// be a double variable;
char a; // Declare a to be a
// character variable;

Assignment Statement
- An assignment statement designates a value for a variable.
- The sign(=) is used as the assignment operator.
- The syntax of assignment statement is as follows:
x = 1; // Assign 1 to x;
radius = 2.7; // Assign 2.7 to radius;
-Its possible to assign a value to the variable when the variable is declared.
(Declaring and Initializing in one step)
-Example:
int x=1;
double radius=2.7;
int x=8, y=3, z=23;
double m1=78, m2=84.5, avg=70.0;
varName=value;

Numeric Data Types
- Every data type has a range of values. The compiler allocates
memory space for each variable or constant according to its
data type.
- Common Numeric Data Types:
 int: integers – simple numbers that do not contain fractional
parts such as : 5, 16477, 0, -14283 .
- Other data types used to store integers are: byte, short, long.
Example: int x =12; int y = 15337; int z = -132; byte a = 13;
 double: real numbers – numbers that include fractional parts
such as : 2.5, -3288.90, -0.0008, 255461.88 .
- Another data type used to store real numbers is float.
Example: double x = 12.2; double y = -100.32; double m = -92.0;

Numeric Data Types

Numeric Data Types
int x=9.5; // yields error, since it can’t store double number into
int variable.
but
double y=9; // it isn’t error, since each integer number is double
number by default

Numeric Data Types
Q: write a program to compute the area of a circle,
suppose radius=2.7 and circle area = R2*π
Q: write a program to compute the net salary of an
employee, suppose tax rate=7%, and employee
salary=800.
tax amount= salary * tax rate.
net salary= salary-tax amount.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education,
Inc. All rights reserved. 0132130807 MODIFIED BY: Abla Hussein

Constants
- A constant is an identifier that represents a permanent value,
that never changes.
- Once constant variable initialized, its value can’t be changed.
- The syntax for declaring a constant variable:
- Example:
- final double p=3.14; // or final double p = 22/7;
final int size = 3;
final datatype constantName=value;

Numeric Operators
- The operators for numeric data types include the standard arithmetic
operators: addition (+), subtraction (–), multiplication (*), division (/),
and remainder (%).
- The operands represent the both sides of an arithmetic operator.
- The syntax for operand and operator is:
- Example:
x + y , 3 * w , 9 – 4 , z / 2 , 8 % 5
operand1 arithmetic operator operand2

Numeric Operators
Result
Example
Meaning
Operator
7
7.0
7.0
5 + 2
5.0 + 2.0
5.0 + 2
Addition
+
7
7.0
7.2
9 – 2
9.0 – 2.0
9 – 1.8
Subtraction
-
10
10.0
10.0
5 * 2
5.0 * 2.0
5.0 * 2
Multiplication
*

Numeric Operators
Result
Example
Meaning
Operator
0
0.5
2
2.5
1 / 2
1.0 / 2
5 / 2
5.0 / 2
Division
/
2
0
3.0
0.2
20 % 3
10 % 10
19.0 % 4
15.2 % 3
Remainder
(mod)
%

Examples
Q: write a program that convert from Fahrenheit to Celsius?
Suppose Fahrenheit degree = 94, where:
Celsius = (5.0/9.0) * (Fahrenheit - 32)
The output should be as following:
The result is:
Fahrenheit Celsius
-------------- ---------
94 34.44
The class name should be FahToCel .
Q: what is the output if we replace (5.0/9.0) with (5/9).

Numeric Operators
- When both operands are integer, the result will be integer.
- When one operand at least is double, the result will be double.
- The % operator known as remainder or modulo operator, which yields
the remainder after division.
Q: write a java program to convert an amount of seconds to minutes,
consider seconds=320.
Q: write a java program to compute how many months, weeks, and
remaining days in an amount of days. Suppose days=293.

Expression
- An expression is a collection of values and variables that are
combined with arithmetic operators.
- Example: A+5*c , 5*6-12%7 , b*c % (4+A)
- An expression can be used as an assignment statement, for
example:
int x= 5*(3/2) – 4;
area=r*r*p;
double avg=(m1+m2+m3)/3;

Evaluating Expression
- Example:
w=
In java, written as:
double w;
w = ( 3 + 4 * x)/5 – 10 * (y – 5) * (a + b + c) / x + 9 * (4/x+ (9 + x) / y)
Q: rewrite the following equation using java:
w=

Precedence Rules
The evaluating of a java expression obeys the following rules:
1. parenthesis ( ), starting from the inner most (from left to
right).
2. * , / , % . (from left to right).
3. + , - . (from left to right).
4. = is applied at the evaluation process.
Example:
x = a + b * c – d / e
x = a + b * c – d / e
1 2
4
3
5

Precedence Rules
Example:
w = a / ((b + c) – d) * (8 – e)
w = a / ((b + c) – d) * (8 – e)
Q: compute the result of the following equation:
y = 6 / 3 + 4 * 8 + 5 – ( 4 + 2 * 7 ) - 1
1 2
4 3
5
6

Print Statement for Variables
- The print statement has three cases:
- Case1: when the content in the parenthesis ( ) is surrounded
by double quotation marks “ ” or single quotation marks ‘ ’.
The content will be printed on the console without any
changes.
- Case2: if the contents is a variable. The last value stored in
the variable will be printed.
- Case3: if the content is a computation process (+,-,*,/,%). The
result of the computation process will be printed on the
console.

Print Statement for Variables
-Example:
System.out.println(“Welcome”); // output is Welcome (Case1).
System.out.println(‘A’); // output is A (Case1).
double sum=20;
System.out.println(sum); // output is 20.0 (Case2).
int x=2, y=7;
System.out.println(x+y); // output is 9 (Case3).
System.out.println(5+8.0); // output is 13.0 (Case3).

Augmented (shortcut) Operators
- The same variable can appear on both sides of assignment operator (
= ).
- Example:
int x=10;
x=x+4;
- The operators +, -, *, /, and % can be combined with the assignment
operator ( = ) to form augmented operators.
- Example:
x += 4;
-the augmented operators are written without space between arithmetic
operators and assignment operator. For example:
x + = 4;// error

Augmented (shortcut) Operators

Increment & Decrement Operators
- The increment operator (++) is for incrementing a variable by one.
- Two types of increment operator:
1. preincrement:
2. postincrement:
- Notice that, the increment operator in both types always increments
the variable by one.
++varName;
varName++;

Example
Assume i = 1
Meaning
Name
Operator
int j= ++i;
//j=2, i=2
Increment var by 1 and use
the new var value in the
current statement
preincrement
++var
int j= i++;
//j=1, i=2
Increment var by 1 but use
the old var value in the
current statement
postincrement
var++
- In preincrement operator, the variable is first incremented
by 1 then the statement is executed.
- But in postincrement operator, statement is first executed
then the variable is incremented by 1.

- The increment operator (--) is for decrementing a variable by
one.
- Two types of increment operator:
1. predecrement:
2. postdecrement:
- Notice that, the decrement operator in both types always
decrements the variable by one.
--varName;
varName--;

Example
Assume i = 1
Meaning
Name
Operator
int j= --i;
//j=0, i=0
Decrement var by 1 and
use the new var value in
the current statement
predecrement
--var
int j= i--;
//j=1, i=0
Decrement var by 1 but
use the old var value in
the current statement
postdecremen
t
var--
- In predecrement operator, the variable is first decremented
by 1 then the statement is executed.
- But in postdecrement operator, statement is first executed
then the variable is decremented by 1.

- Example:
int i=10;
int newnum=10 * i++;
// newnum= 100, and i=11.
int i=10;
int newnum= 10 * ++i;
// newnum=110, i=11.

int i= 3;
i++;
System.out.println(i); //4
++i;
System.out.println(--i); //4
--i;
i--;
System.out.println(i--); //2
System.out.println(--i); //0
i++;
System.out.println(i++); //1

Numeric Data Type Casting
- Casting: is an operation that converts a value of one data type
into a value of another data type.
- Two Types of casting:
1. widening casting: the casting of a type with a small range to a
type with a larger range. (usually done automatically by
compiler).
Example:
int x=5; byte k=8;
double y=x; long m=k;
short a=-12;
int b=a;

- Casting: is an operation that converts a value of one data type
into a value of another data type.
- Two Types of casting:
2. narrowing casting: the casting of a type with a large range to a
type with a smaller range. (must be done explicitly using code).
Example:
double a=3.8;
int b=a; // error
int x=5;
short y=x; // error

- The syntax for narrowing casting:
Example:
(new datatype) varName(or value);
double a=3.8;
int b= (int) a; // b=3
int x= (int) 5.9; // x=5
int y = (int) 8.0; // y=8
double a= -53.2440;
int b= (int) a; // b= -53

Note that:
- Casting does not change the variable being cast. For example, d is
not changed after casting in the following code:
int x = 5 / 2.0; // error
int x = (int) (5 / 2.0); // x = 2
double d = 4.5;
int i = (int)d; // i becomes 4, but d is still 4.5

Byte
Short
Int
Long
Float
double
Small Range
Large Range
Narrowing
Casting
(Explicitly)
Widening
Casting
(Automatically)

- Take care about operands types in arithmetic operators. When one
operand is double the another value are automatically converted into
double.
Q: write a program to display the number 26.31597 with two digits after
the decimal point.(i.e. the output should be 26.31).

Precedence Rules
1. parenthesis ( ), starting from the inner most (from left to right).
2. var++ , var-- (from right to left).
3. ++var , --var , unary + , unary - (from right to left).
4. (type casting) (from right to left).
5. * , / , % . (from left to right).
6. + , - . (from left to right).
7. = , += , -= , *= , /= , %= (is applied at the evaluation process).

Precedence Rules
Example:
Solution:
d -= 1.5 * 3 + 1
d -= 4.5 + 1
d = 1.0-5.5 // d= d- 5.5
d = -4.5
d=1.0, a= 1;
d -= 1.5 * 3 + a++;

Precedence Rules
Q: what is the output of the following equation:
- Notice that, if there isn’t parenthesis enclosed the next expression after
the type casting, only the first value (or variable) after the type casting
will be casted.
- Suppose that you declare variable k as int, is there a syntax Error? Why
no?
- Delete the augmented operator and replace it with just = sign. Error?
Why yes?
int b=3, c=2;
double a=9,k=2;
k += (int) (a/2) * ++b – c++ + (double) 5 / 2 ;

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