Loops in Java are used to execute a block of code repeatedly until a specific condition is met. Java supports several types of loops:

1. while Loop

The while loop executes a block of code as long as a specified condition is true.

  public class Main {
    public static void main(String[] args) {
        int i = 1;
        while (i <= 5) {
            System.out.println("Count is: " + i);
            i++;
        }
    }
}

2. do-while Loop

The do-while loop is similar to the while loop, but it executes the block of code at least once before checking the condition.

  public class Main {
    public static void main(String[] args) {
        int i = 1;
        do {
            System.out.println("Count is: " + i);
            i++;
        } while (i <= 5);
    }
}

3. for Loop

The for loop is used when you know exactly how many times you want to execute a block of code.

  public class Main {
    public static void main(String[] args) {
        for (int i = 1; i <= 5; i++) {
            System.out.println("Count is: " + i);
        }
    }
}

4. for-each Loop

The for-each loop is used to iterate through elements of an array or a collection.

  public class Main {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3, 4, 5};
        for (int number : numbers) {
            System.out.println("Number is: " + number);
        }
    }
}

Loop Control Statements

Java provides loop control statements break and continue to control the execution flow of loops:

break Statement

The break statement terminates the loop and transfers control to the next statement outside the loop.

  public class Main {
    public static void main(String[] args) {
        for (int i = 1; i <= 5; i++) {
            if (i == 3) {
                break;
            }
            System.out.println("Count is: " + i);
        }
    }
}

continue Statement

The continue statement skips the current iteration of the loop and proceeds to the next iteration.

  public class Main {
    public static void main(String[] args) {
        for (int i = 1; i <= 5; i++) {
            if (i == 3) {
                continue;
            }
            System.out.println("Count is: " + i);
        }
    }
}

Nested Loops 

  for (int row = 1; row <= 3; row++) {
    for (int col = 1; col <= 3; col++) {
        System.out.printf("(%d,%d) ", row, col);
    }
    System.out.println();
}

Watch total iterations — a double loop over 1000×1000 elements runs one million times.

Labeled break and continue

Break out of an outer loop from an inner loop:

  outer:
for (int i = 0; i < 10; i++) {
    for (int j = 0; j < 10; j++) {
        if (i * j > 50) break outer;
        System.out.println(i * j);
    }
}

Use labels sparingly — extracting a method is often clearer.

Choosing the Right Loop

Loop Best for
for Known iteration count, index needed
while Condition checked before each iteration
do-while At least one execution guaranteed
for-each Iterating collections or arrays

Common Loop Patterns 

  // Sum array
int sum = 0;
for (int n : numbers) sum += n;

// Find first match
OptionalInt first = IntStream.of(numbers).filter(n -> n > 10).findFirst();

// Reverse iteration
for (int i = list.size() - 1; i >= 0; i--) {
    process(list.get(i));
}

Infinite Loop Pitfalls 

  while (true) { /* server event loop — intentional */ }

while (count < 10) {
    // forgot to increment count — infinite loop!
}

Always ensure the loop condition eventually becomes false (unless intentionally infinite).