Loops in Java

Java While Loop

Loops

Loops can execute a block of code as long as a specified condition is reached.

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1)Java While Loop

The while loop loops through a block of code as long as a specified condition is true:

In the example below, the code in the loop will run, over and over again, as long as a variable (i) is less than 5:

Example

public class MyClass

{
public static void main(String[] args)

{
int i = 0;
while (i < 5) {
System.out.println(i);
i++;
}
}
}

The Do/While Loop

The do/while loop is a variant of the while loop. This loop will execute the code block once, before checking if the condition is true, then it will repeat the loop as long as the condition is true.

The example below uses a do/while loop. The loop will always be executed at least once, even if the condition is false, because the code block is executed before the condition is tested:

Example

public class MyClass

{
public static void main(String[] args)

{
int i = 0;
do {
System.out.println(i);
i++;
}
while (i < 5);
}
}

2)Java For Loop

When you know exactly how many times you want to loop through a block of code, use the for loop instead of a while loop:

Statement 1 is executed (one time) before the execution of the code block.

Statement 2 defines the condition for executing the code block.

Statement 3 is executed (every time) after the code block has been executed.

The example below will print the numbers 0 to 4:

Example

public class MyClass {
public static void main(String[] args) {
for (int i = 0; i < 5; i++) {
System.out.println(i);
}
}
}

Example explained

Statement 1 sets a variable before the loop starts (int i = 0).

Statement 2 defines the condition for the loop to run (i must be less than 5). If the condition is true, the loop will start over again, if it is false, the loop will end.

Statement 3 increases a value (i++) each time the code block in the loop has been executed.

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Another Example

This example will only print even values between 0 and 10:

Example

public class MyClass {
public static void main(String[] args) {
for (int i = 0; i <= 10; i = i + 2) {
System.out.println(i);
}
}
}

Example

public class MyClass

{
public static void main(String[] args)

{
String[] cars = {“Volvo”, “BMW”, “Ford”, “Mazda”};
for (String i : cars)

{
System.out.println(i);
}
}
}