OOP with Java Programming
Dr. Ahmed Al-Salih
2rd class – Department of Programming
College of IT- University of Babylon
Java Translation
• The Java compiler translates Java source code into a special
representation called bytecode
• Java bytecode is not the machine language for any traditional CPU
• Another software tool, called an interpreter, translates bytecode into
machine language and executes it
• Therefore the Java compiler is not tied to any particular machine
• Java is considered to be architecture-neutral
Java Translation
Java source
code
Java
compiler
Java
bytecode
Bytecode
interpreter
Bytecode
compiler
Machine
code
Input in Java:
JOptionPane is a easy way to do dialog boxes, messages or inputs. You
have to import it at the beginning of the program:
//A sample program. Sample.java
import javax.swing.JOptionPane; // imports JOptionPane class
public class Sample {
public static void main ( String args[] )
{
JOptionPane.showMessageDialog ( null, "This is a sample program" );
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OOP with Java Programming
Dr. Ahmed Al-Salih
2rd class – Department of Programming
College of IT- University of Babylon
System.exit ( 0 ); //stops the program
}
}
There are different kinds of icons for a dialog box, just replace the last argument:
JOptionPane.PLAIN_MESSAGE // this is a plain message
JOptionPane.INFORMATION_MESSAGE // this is a info message
JOptionPane.ERROR_MESSAGE // this is a error message
JOptionPane.WARNING_MESSAGE // this is a warning message
You can also use JOptionPane for dialog boxes for input, and assign them to variables,
just put:
name=
JOptionPane.showInputDialog("put your message here" );
Example
import javax.swing.JOptionPane; //import class JOptionPane
public class Addition {
public static void main ( String args[] )
{
String firstNumber, secondNumber;
int number1, number2,
sum;
//read in the first number from user as a string
firstNumber = JOptionPane.showInputDialog ( "Enter first
integer" );
//read in the second number from user as a string
secondNumber =JOptionPane.showInputDialog ( "Enter second
interger");
//convert numbers from type String to type int
number1 = Integer.parseInt ( firstNumber);
number2 = Integer.parseInt ( secondNumber);
//add the numbers
sum = number1 + number2;
//display the results
JOptionPane.showMessageDialog ( null, "The sum is " +
sum,"Results",JOptionPane.PLAIN_MESSAGE);
System.exit ( 0 ); //ends the program
} }
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OOP with Java Programming
Dr. Ahmed Al-Salih
2rd class – Department of Programming
College of IT- University of Babylon
 Java basic operator:
We can divide all the Java operators into the following groups:





Arithmetic Operators
Relational Operators
Bitwise Operators
Logical Operators
Assignment Operators
1- The Arithmetic Operators:
Arithmetic operators are used in mathematical expressions in the same way that they
are used in algebra. The following table lists the arithmetic operators: Assume integer
variable A holds 10 and variable B holds 20
2- The Relational Operators:
There are following relational operators supported by Java language:
Assume variable A holds 10 and variable B holds 20, then:
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OOP with Java Programming
Dr. Ahmed Al-Salih
2rd class – Department of Programming
College of IT- University of Babylon
3- The Bitwise Operators:
Java defines several bitwise operators, which can be applied to the integer types, long,
int, short, char, and byte.
Bitwise operator works on bits and performs bit-by-bit operation. Assume if a = 60;
and b = 13; now in binary format they will be as follows:
a = 0011 1100
b = 0000 1101
Assume integer variable A holds 60 and variable B holds 13, then:
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OOP with Java Programming
Dr. Ahmed Al-Salih
2rd class – Department of Programming
College of IT- University of Babylon
4- The Logical Operators:
The following table lists the logical operators:
Assume Boolean variables A holds true and variable B holds false, then:
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OOP with Java Programming
Dr. Ahmed Al-Salih
2rd class – Department of Programming
College of IT- University of Babylon
5- The Assignment Operators:
There are following assignment operators supported by Java language:
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OOP with Java Programming
Dr. Ahmed Al-Salih
2rd class – Department of Programming
College of IT- University of Babylon
 Java Decision Making:
There are two types of decision making statements in Java. They are:
 if statements
 switch statements
The if Statement:
An if statement consists of a Boolean expression followed by one or more statements.
Syntax:
The if...else Statement:
An if statement can be followed by an optional else statement, which executes when
the Boolean expression is false.
Syntax:
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OOP with Java Programming
Dr. Ahmed Al-Salih
2rd class – Department of Programming
College of IT- University of Babylon
The if...else if...else Statement:
Syntax:
Nested if...else Statement:
It is always legal to nest if-else statements which means you can use one if or else if
statement inside another if or else if statement.
Syntax:
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OOP with Java Programming
Dr. Ahmed Al-Salih
2rd class – Department of Programming
College of IT- University of Babylon
The switch Statement:
A switch statement allows a variable to be tested for equality against a list of values.
Each value is called a case, and the variable being switched on is checked for each
case.
Syntax:
Public class Test{
Public static void main(String args[]){
switch(grade)
{
case'A':
System.out.println("Excellent!");
break;
case'B':
case'C':
System.out.println("Well done");
break;
case'D':
System.out.println("You passed");
case'F':
System.out.println("Better try again");
break;
default:
System.out.println("Invalid grade");
}
System.out.println("Your grade is "+ grade);
}
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OOP with Java Programming
Dr. Ahmed Al-Salih
2rd class – Department of Programming
College of IT- University of Babylon
}
Java numbers
Number Methods:
SN
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
22
Methods with Description
xxxValue( ) Converts the value of this Number object to the xxx data type and
returned it.
compareTo ( ) Compares this Number object to the argument.
Equals ( ) Determines whether this number object is equal to the argument.
valueOf( ) Returns an Integer object holding the value of the specified primitive.
toString( ) Returns a String object representing the value of specified int or
Integer.
parseInt( ) This method is used to get the primitive data type of a certain String.
abs( ) Returns the absolute value of the argument.
ceil( ) Returns the smallest integer that is greater than or equal to the argument.
Returned as a double.
floor( ) Returns the largest integer that is less than or equal to the argument.
Returned as a double.
rint( ) Returns the integer that is closest in value to the argument. Returned as a
double.
round( ) Returns the closest long or int, as indicated by the method's return type,
to the argument.
min( ) Returns the smaller of the two arguments.
max( ) Returns the larger of the two arguments.
exp( ) Returns the base of the natural logarithms, e, to the power of the argument.
log( ) Returns the natural logarithm of the argument.
pow( ) Returns the value of the first argument raised to the power of the second
argument.
sqrt( ) Returns the square root of the argument.
sin( ) Returns the sine of the specified double value.
cos( ) Returns the cosine of the specified double value.
tan( ) Returns the tangent of the specified double value.
asin( ) Returns the arcsine of the specified double value.
acos( ) Returns the arccosine of the specified double value.
atan( ) Returns the arctangent of the specified double value.
atan2( ) Converts rectangular coordinates (x, y) to polar coordinate (r, theta) and
returns theta.
OOP with Java Programming
Dr. Ahmed Al-Salih
25
26
27
2rd class – Department of Programming
College of IT- University of Babylon
toDegrees( ) Converts the argument to degrees
toRadians( ) Converts the argument to radians.
random() Returns a random number
Java Loop Controls:
You can use one of the following three loops:
 while Loop
 do...while Loop
 for Loop
1- The while Loop:
A while loop is a control structure that allows you to repeat a task a certain number of
times.
Syntax:
The syntax of a while loop is:
while(Boolean_expression)
{
//Statements
}
Example:
Public class Test{
Public static void main(String args[]){
int x =10;
while( x <20){
System.out.print("value of x : "+ x );
x++;
System.out.print("\n");
}
} }
2- The do...while Loop:
A do...while loop is similar to a while loop, except that a do...while loop is guaranteed
to execute at least one time.
Syntax:
The syntax of a do...while loop is:
do
{
//Statements
}while(Boolean_expression);
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OOP with Java Programming
Dr. Ahmed Al-Salih
2rd class – Department of Programming
College of IT- University of Babylon
Example:
Public class Test{
Public static void main(String args[]){
int x =10;
do{
System.out.print("value of x : "+ x );
x++;
System.out.print("\n");
}while( x <20);
}
}
3- The for Loop:
A for loop is a repetition control structure that allows you to efficiently write a loop
that needs to execute a specific number of times.
A for loop is useful when you know how many times a task is to be repeated.
Syntax:
The syntax of a for loop is:
for(initialization;Boolean_expression; update)
{
//Statements
}
Example:
Public class Test{
Public static void main(String args[]){
for(int x =10; x <20; x = x+1){
System.out.print("value of x : "+ x );
System.out.print("\n");
}
}
}
The break Keyword:
The break keyword is used to stop the entire loop. The break keyword must be used
inside any loop or a switch statement.
Syntax: The syntax of a break is a single statement inside any loop:
break;
24
OOP with Java Programming
Dr. Ahmed Al-Salih
2rd class – Department of Programming
College of IT- University of Babylon
Example:
Public class Test{
public static void main(String args[]){
for(int x =10; x <50; x = x+10){
if( x ==30){
break; }
System.out.print( x );
System.out.print("\n");
}
}
}
The output:
10
20
The continue Keyword:
The continue keyword can be used in any of the loop control structures. It causes the
loop to immediately jump to the next iteration of the loop.
 In a for loop, the continue keyword causes flow of control to immediately jump
to the update statement.
 In a while loop or do/while loop, flow of control immediately jumps to the
Boolean expression.
Syntax:
The syntax of a continue is a single statement inside any loop:
continue;
Example:
Public class Test{
Public static void main(String args[]){
for(int x =10; x <50; x = x+10){
if( x ==30){
continue; }
System.out.print( x );
System.out.print("\n");
}
}
}
The output:
10
20
40
50
25