Java for Loop

The for loop in Java is a control flow statement that is used to repeatedly execute a block of code for a specific number of iterations. It is particularly useful when you know beforehand how many times the loop needs to run.

Syntax:

for (initialization; condition; increment/decrement) {
    // Code to be executed
}

Explanation

1. Initialization: This is executed only once at the beginning of the loop. It is typically used to declare and initialize the loop control variable.

2. Condition: This is evaluated before each iteration. If the condition evaluates to true, the loop continues; otherwise, the loop stops.

3. Update: This is executed after each iteration and is usually used to update the loop control variable.

Example: print value from 1 to 5 through for loop

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

Output:

Working Process:

1. Initialization: int i = 1; sets the loop control variable i to 1.

2. Condition: i <= 5; checks if i is less than or equal to 5.

3. Body Execution: The code inside the loop (System.out.println) is executed.

4. Update: i++ increments i by 1 after each iteration.

For Each loop

A for-each Style loop is designed to cycle through a collection of objects, such as an array, in a strictly sequential fashion, from start to finish. Unlike some languages, such as C#, that implement a for-each loop by using the keyword foreach, Java adds the for-each capability by enhancing the for statement. The advantage of this approach is that no new keyword is required, and no preexisting code is broken.

The for-each style of for is also referred to as the enhanced for loop.

The general form of the for-each version of the for is shown here:

Syntax:

    for(type itr-var : collection) statement-block

Example:

  // Use a for-each style for loop.
class ForEach {
public static void main(String args[]) {
int nums[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
int sum = 0;
// use for-each style for to display and sum the values
for(int x : nums) {
System.out.println("Value is: " + x);
sum += x;
}
System.out.println("Summation: " + sum);
}
}

Reverse Loop

Loops can count down instead of up.

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

Output:

Nested for Loop

You can use one for loop inside another to handle multidimensional scenarios, like printing patterns.

public class NestedForLoop {
    public static void main(String[] args) {
        for (int i = 1; i <= 3; i++) {
            for (int j = 1; j <= 3; j++) {
                System.out.println("i: " + i + ", j: " + j);
            }
        }
    }
}

Output:

Enhanced for Loop (for-each Loop)

Used to iterate over arrays or collections.

Example with Arrays:

public class ForEachLoop {
    public static void main(String[] args) {
        int[] numbers = {10, 20, 30, 40, 50};
        for (int num : numbers) {
            System.out.println(num);
        }
    }
}

Output:

Skipping a Loop

Skip the current iteration and move to the next.

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

Output:

Using break

Exit the loop prematurely.

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

Output:

Infinite Loop

A for loop can run indefinitely if no stopping condition is provided.

public class InfiniteLoop {
    public static void main(String[] args) {
        for (;;) {
            System.out.println("This is an infinite loop.");
        }
    }
}

Java for Loop – Interview Questions

Java For Loop – Objective Questions (MCQs)

for (int i = 1; i <= 5; i++) {
System.out.println(i);
}

for (int i = 0; i < 3; i++) {
System.out.print(i + ' ');
}

int sum = 0;
for (int i = 1; i <= 3; i++) {
sum += i;
}
System.out.println(sum); 

Related Java For Loop Topics