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Loops in Java: for, while, do-while, and Control Statements (break and continue)

Loops are essential in programming because they allow us to repeatedly execute a block of code. In Java, there are three primary types of loops: for loop, while loop, and do-while loop. We'll also cover control statements like break and continue that can modify the flow of loops. Finally, we'll explore nested loops, where one loop is inside another.

for Loop

The for loop is generally used when you know the number of iterations ahead of time. It consists of three parts: initialization, condition, and increment/decrement.

Syntax:

    
    for (initialization; condition; update) {
        // code block to be executed
    }
    
    

• Initialization: Sets up the loop (e.g., int i = 0).
• Condition: The loop continues as long as this condition is true (e.g., i < 10).
• Update: Typically increments or decrements the loop variable (e.g., i++).

Example:

    
    public class ForLoopExample {
        public static void main(String[] args) {
            // Print numbers 0 to 9
            for (int i = 0; i < 10; i++) {
                System.out.println(i);
            }
        }
    }
    
    

Output:

    
    0
    1
    2
    3
    4
    5
    6
    7
    8
    9
    
    

while Loop

The while loop is used when the number of iterations is not known beforehand. The loop will continue as long as the condition is true.

Syntax:

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

Example:

    
    public class WhileLoopExample {
        public static void main(String[] args) {
            int i = 0;

            // Print numbers 0 to 9
            while (i < 10) {
                System.out.println(i);
                i++; // Increment the counter
            }
        }
    }
    
    

Output:

    
    0
    1
    2
    3
    4
    5
    6
    7
    8
    9
    
    

do-while Loop

The do-while loop is similar to the while loop, except that the condition is checked after the code block is executed. This means the code inside the loop is always executed at least once.

Syntax:

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

Example:

    
    public class DoWhileLoopExample {
        public static void main(String[] args) {
            int i = 0;

            // Print numbers 0 to 9
            do {
                System.out.println(i);
                i++; // Increment the counter
            } while (i < 10);
        }
    }
    
    

Output:

    
    0
    1
    2
    3
    4
    5
    6
    7
    8
    9
    
    

• Even though i is initially 0, the condition is checked after the loop runs, so the loop body is executed at least once.

break and continue Statements

• break: The break statement is used to exit a loop prematurely, regardless of the condition.
• continue: The continue statement is used to skip the current iteration and proceed with the next iteration of the loop.

Example with break

    
    public class BreakExample {
        public static void main(String[] args) {
            for (int i = 0; i < 10; i++) {
                if (i == 5) {
                    break; // Exit the loop when i equals 5
                }
                System.out.println(i);
            }
        }
    }
    
    

Output:

    
    0
    1
    2
    3
    4
    
    

• The loop stops when i equals 5 due to the break statement.

Example with continue

    
    public class ContinueExample {
        public static void main(String[] args) {
            for (int i = 0; i < 10; i++) {
                if (i == 5) {
                    continue; // Skip this iteration when i equals 5
                }
                System.out.println(i);
            }
        }
    }
    
    

Output:

    
    0
    1
    2
    3
    4
    6
    7
    8
    9
    
    

• The loop skips the iteration when i equals 5 and continues with the next iteration.

Nested Loops

A nested loop is a loop inside another loop. You can nest any type of loop inside another loop. The inner loop is executed completely each time the outer loop runs.

Syntax:

    
    for (int i = 0; i < outerCondition; i++) {
        for (int j = 0; j < innerCondition; j++) {
            // Code to execute for inner loop
        }
    }
    
    

Example with Nested Loops (for loops):

    
    public class NestedLoopExample {
        public static void main(String[] args) {
            // Print a 3x3 grid of numbers
            for (int i = 1; i <= 3; i++) {
                for (int j = 1; j <= 3; j++) {
                    System.out.print(i * j + " "); // Print the product of i and j
                }
                System.out.println(); // Move to the next line after each inner loop iteration
            }
        }
    }
    
    

Output:

    
    1 2 3 
    2 4 6 
    3 6 9 
    
    

• The outer loop runs 3 times, and for each iteration of the outer loop, the inner loop runs 3 times, resulting in a 3x3 grid.

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