JavaTechGeeks

A Guide To Loops In Java

25 September 2023
Java offers several loop constructs that empower you to execute a block of code repeatedly, making them invaluable for managing program flow and handling repetitive tasks automatically. This guide will walk you through Java’s three primary loop types—for, while, and do-while loops—each with its unique use cases and structure.

For Loop

The for loop is ideal when you know beforehand how many times you need to run a code block. Its structure is compact and powerful, with three integral components: initialization, condition, and iteration.
  • Initialization: This step initializes a control variable for the loop, setting it up for the first iteration.
  • Condition: A logical statement is evaluated before each iteration; the loop will continue as long as it remains true.
  • Iteration: Defines how the control variable is modified after each iteration, guiding the loop towards its termination.
The for loop’s straightforward design is perfect for scenarios where the number of iterations is known, such as traversing arrays or performing operations a set number of times. Here’s a quick example of a basic for loop:
				
					// Syntax

for (initialization; condition; iteration) {
    // Code to be repeated
}

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

In this example, the loop initializes i to 0, executes the code block as long as i is less than 5, and increments i by 1 after each iteration.

While Loop:

The while loop is used when you want to repeat a block of code as long as a specified condition is true. It checks the condition before entering the loop.

				
					// Syntax

while (condition) {
    // Code to be repeated
}

//Example
int count = 1;
while (count <= 5) {
    System.out.println("Iteration " + count);
    count++;
}

Here, we manually initialize count before the loop and increment it within the loop until the condition becomes false.

Do-While Loop:

The do-while loop is similar to the while loop, but it guarantees that the block of code will be executed at least once because it checks the condition after the code block.

				
					// Syntax
do {
    // Code to be repeated
} while (condition);


//Example

int count = 1;
do {
    System.out.println("Iteration " + count);
    count++;
} while (count <= 5);

This loop will always run at least once, even if the condition is initially false.

Loop Control Statements:

Java provides loop control statements that allow you to alter the flow of loops:
    • break: Terminates the loop prematurely, and control is transferred to the code immediately after the loop.
    • continue: Skips the rest of the current iteration and proceeds to the next loop iteration.
    • return: Can be used to exit from a method and, indirectly, from a loop.
				
					// Using break to exit a loop
for (int i = 0; i < 10; i++) {
    if (i == 5) {
        break;
    }
    System.out.println("Iteration " + i); // This will print numbers from 0 to 4.
}

// Using continue to skip an iteration
for(int i = 0; i < 10; i++) {
    if(i == 5) {
        continue;
    }
    System.out.println(i); // This will print numbers from 0 to 9, but not 5.
}

Remember to be cautious when writing loops. An incorrectly coded condition might result in an infinite loop, which will run indefinitely until the program is stopped or crashes. Always keep your loop termination condition in mind and ensure that it will eventually become false to exit the loop.