Java Loops

Loops in Java are used to execute a block of code repeatedly based on a condition. Java provides several types of loops, each with specific use cases. The primary loop types are for, while, and do-while.

1. For Loop

The for loop is used when the number of iterations is known beforehand. It consists of three parts: initialization, condition, and update:

for (initialization; condition; update) {
    // code to execute on each iteration
}

Example:

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

This loop will print numbers from 0 to 4. The loop initializes i to 0, runs as long as i < 5, and increments i by 1 after each iteration.

2. While Loop

The while loop is used when the number of iterations is not known and depends on a condition. It continues to execute as long as the condition remains true:

while (condition) {
    // code to execute on each iteration
}

Example:

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

This loop will also print numbers from 0 to 4. The condition i < 5 is checked before each iteration, and i is incremented inside the loop.

3. Do-While Loop

The do-while loop is similar to the while loop, but it guarantees that the code block will execute at least once, as the condition is evaluated after the loop body:

do {
    // code to execute on each iteration
} while (condition);

Example:

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

This loop will print numbers from 0 to 4. The code block executes first, then the condition i < 5 is checked.

4. Enhanced For Loop

The enhanced for loop (also known as the "for-each" loop) is used to iterate over arrays or collections. It simplifies iteration without using an index:

for (type item : array) {
    // code to execute for each item
}

Example:

int[] numbers = {1, 2, 3, 4, 5};
for (int number : numbers) {
    System.out.println(number);
}

This loop iterates over the numbers array and prints each element.

5. Break and Continue Statements

The break statement is used to exit a loop prematurely, while the continue statement skips the current iteration and proceeds to the next iteration:

• Break Statement:

  for (int i = 0; i < 10; i++) {
      if (i == 5) {
          break;
      }
      System.out.println(i);
  }

  This loop will print numbers from 0 to 4, then exit the loop when i equals 5.

• Continue Statement:

  for (int i = 0; i < 10; i++) {
      if (i % 2 == 0) {
          continue;
      }
      System.out.println(i);
  }

  This loop will print only odd numbers between 0 and 9, skipping even numbers.

6. Labeled Loops

Labeled loops can be used to break or continue from nested loops. A label is specified before the loop, and can be used with the break or continue statements to specify which loop to affect:

outerLoop: for (int i = 0; i < 5; i++) {
    for (int j = 0; j < 5; j++) {
        if (j == 2) {
            break outerLoop;
        }
        System.out.println("i = " + i + ", j = " + j);
    }
}

This example will exit the outer loop when j equals 2, printing values of i and j before the exit.