Loops in Java

Loops can execute a block of code as long as a specified condition is reached. They are handy because they save time, reduce errors, and they make code more readable.

While Loop

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

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

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:

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

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. Syntax:

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

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:

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

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. Syntax:

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

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:

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

For-Each Loop

There is also a “for-each” loop, which is used exclusively to loop through elements in an array. Syntax:

for (type variableName : arrayName) {
  // code block to be executed
}

The break statement can also be used to jump out of a loop.

This example jumps out of the loop when i is equal to 4:

for (int i = 0; i < 10; i++) {
  if (i == 4) {
    break;
  }
  System.out.println(i);
}

Java Continue

The continue statement breaks one iteration (in the loop), if a specified condition occurs, and continues with the next iteration in the loop.

This example skips the value of 4:

for (int i = 0; i < 10; i++) {
  if (i == 4) {
    continue;
  }
  System.out.println(i);
}