Java Loop Control

There may be a situation when you need to execute a block of code several numbers of times. In general, statements are executed sequentially: The first statement in a function is executed first, followed by the second, and so on.

Programming languages provide various control structures that allow for more complicated execution paths.

loop statement allows us to execute a statement or group of statements multiple times and following is the general form of a loop statement in most of the programming languages −

We have a different type of Loops in Java.

While Loop

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

Syntex

while (condition) {
  // code block to be executed
}

Example

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:

int i = 0;
while (i < 15) {
  System.out.println(i);
  i++;
}

 

For Loop

The for loop loops through a block of code a number of times.

Syntex

for (statement 1; statement 2; statement 3) {
  // code block to be executed
}

Example

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 14

for (int i = 0; i < 15; 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.

 

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.

Syntex

do {
  // code block to be executed
}
while (condition);

Example

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:

int i = 0;
do {
  System.out.println(i);
  i++;
}
while (i < 15);