Java Loop Control
There may be a sitution when we need to execute a block of code several number of times, and is often referred to as a loop.
Java has very flexible looping mechanisms
Looping Mechanisms
Java has very flexible three looping mechanisms. You can use one of the following three loops:
· while Loop
· do...while Loop
· for Loop
As of java 5 the enhanced for loop was introduced. This is mainly used for Arrays.
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
}
When executing, if the boolean_expression result is true then the actions inside the loop will be executed. This will continue as long as the expression result is true.
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");
}
}
}
This would produce following result:
value of x : 10
value of x : 11
value of x : 12
value of x : 13
value of x : 14
value of x : 15
value of x : 16
value of x : 17
value of x : 18
value of x : 19
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);
If the Boolean expression is true, the flow of control jumps back up to do, and the statements in the loop execute again. This process repeats until the Boolean expression is false.
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 );
}
}
This would produce following result:
value of x : 10
value of x : 11
value of x : 12
value of x : 13
value of x : 14
value of x : 15
value of x : 16
value of x : 17
value of x : 18
value of x : 19
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");
}
}
}
This would produce following result:
value of x : 10
value of x : 11
value of x : 12
value of x : 13
value of x : 14
value of x : 15
value of x : 16
value of x : 17
value of x : 18
value of x : 19
Enhanced for loop in Java:
As of java 5 the enhanced for loop was introduced. This is mainly used for Arrays.
Syntax:
The syntax of enhanced for loop is:
for(declaration : expression)
{
//Statements
}
· Declaration . The newly declared block variable, which is of a type compatible with the elements of the array you are accessing. The variable will be available within the for block and its value would be the same as the current array element.
· Expression . This evaluate to the array you need to loop through. The expression can be an array variable or method call that returns an array.
Example:
public class Test {
public static void main(String args[]){
int [] numbers = {10, 20, 30, 40, 50};
for(int x : numbers ){
System.out.print( x );
System.out.print(",");
}
System.out.print("\n");
String [] names ={"Jhon", "Lewis", "Tom", "Lara"};
for( String name : names ) {
System.out.print( name );
System.out.print(",");
}
}
}
Output
10,20,30,40,50,
Jhon,Lewis,Tom,Lara,
There may be a sitution when we need to execute a block of code several number of times, and is often referred to as a loop.
Java has very flexible looping mechanisms
Looping Mechanisms
Java has very flexible three looping mechanisms. You can use one of the following three loops:
· while Loop
· do...while Loop
· for Loop
As of java 5 the enhanced for loop was introduced. This is mainly used for Arrays.
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
}
When executing, if the boolean_expression result is true then the actions inside the loop will be executed. This will continue as long as the expression result is true.
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");
}
}
}
This would produce following result:
value of x : 10
value of x : 11
value of x : 12
value of x : 13
value of x : 14
value of x : 15
value of x : 16
value of x : 17
value of x : 18
value of x : 19
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);
If the Boolean expression is true, the flow of control jumps back up to do, and the statements in the loop execute again. This process repeats until the Boolean expression is false.
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 );
}
}
This would produce following result:
value of x : 10
value of x : 11
value of x : 12
value of x : 13
value of x : 14
value of x : 15
value of x : 16
value of x : 17
value of x : 18
value of x : 19
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");
}
}
}
This would produce following result:
value of x : 10
value of x : 11
value of x : 12
value of x : 13
value of x : 14
value of x : 15
value of x : 16
value of x : 17
value of x : 18
value of x : 19
Enhanced for loop in Java:
As of java 5 the enhanced for loop was introduced. This is mainly used for Arrays.
Syntax:
The syntax of enhanced for loop is:
for(declaration : expression)
{
//Statements
}
· Declaration . The newly declared block variable, which is of a type compatible with the elements of the array you are accessing. The variable will be available within the for block and its value would be the same as the current array element.
· Expression . This evaluate to the array you need to loop through. The expression can be an array variable or method call that returns an array.
Example:
public class Test {
public static void main(String args[]){
int [] numbers = {10, 20, 30, 40, 50};
for(int x : numbers ){
System.out.print( x );
System.out.print(",");
}
System.out.print("\n");
String [] names ={"Jhon", "Lewis", "Tom", "Lara"};
for( String name : names ) {
System.out.print( name );
System.out.print(",");
}
}
}
Output
10,20,30,40,50,
Jhon,Lewis,Tom,Lara,