Java programming language provides the following types of loop to handle looping requirements :
A while loop statement in Java programming language repeatedly executes a target statement as long as a given condition is true.
while(Boolean_expression) {
// Statements
}
Here, statement(s) may be a single statement or a block of statements. The condition may be any expression, and true is any non zero value.
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.
When the condition becomes false, program control passes to the line immediately following the loop.
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");
}
}
}
for(initialization; Boolean_expression; update) {
// Statements
}
This is how it works :
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");
}
}
}
A do...while loop is similar to a while loop, except that a do...while loop is guaranteed to execute at least one time.
do {
// Statements
}while(Boolean_expression);
Notice that the Boolean expression appears at the end of the loop, so the statements in the loop execute once before the Boolean is tested.
If the Boolean expression is true, the control jumps back up to do statement, and the statements in the loop execute again. This process repeats until the Boolean expression is false.
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 );
}
}
As of Java 5, the enhanced for loop was introduced. This is mainly used to traverse collection of elements including arrays.
for(declaration : expression) {
// Statements
}
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 = {"James", "Larry", "Tom", "Lacy"};
for( String name : names ) {
System.out.print( name );
System.out.print(",");
}
}
}