Java For Loop

Introduction to For Loop

The for loop is one of the most commonly used looping structures in Java. It allows you to repeatedly execute a block of code a specific number of times. The for loop is particularly useful when you know beforehand how many times a task needs to be repeated. It is concise, flexible, and makes iterative programming easy to read and maintain

Syntax of For Loop

for (initialization; condition; update) {
    // Code to execute in each iteration
}

• Initialization: This is executed once at the start of the loop. It is used to initialize the loop control variable(s).
• Condition: This is evaluated before each iteration. If the condition is true, the loop body executes. If false, the loop terminates.
• Update: This is executed after each iteration to update the loop control variable(s).

Key Points About For Loop

1. Deterministic Loop:
   • The for loop is ideal when you know the exact number of iterations.
2. Compact Syntax:
   • The initialization, condition and update statements are all written in a single line, making the loop compact and readable.
3. Avoids Infinite Loops:
   • With proper initialization, condition and update, the for loop minimizes the chances of infinite looping.
4. Flowchart of For Loop
5. Execute the initialization statement.
6. Check the condition.
7. If the condition is true, execute the loop body.
8. Update the loop variable(s).
9. Repeat steps 2–4 until the condition evaluates to false.

Examples of For Loop

Example 1: Print Numbers from 1 to 5

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

Output:

Number: 1  
Number: 2  
Number: 3  
Number: 4  
Number: 5

Example 2: Sum of First 10 Natural Numbers

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

        for (int i = 1; i <= 10; i++) {
            sum += i; // Add i to sum
        }

        System.out.println("Sum of first 10 natural numbers: " + sum);
    }
}

Output:

Sum of first 10 natural numbers: 55

Example 3: Printing an Array Using For Loop

public class ArrayExample {
    public static void main(String[] args) {
        int[] numbers = {2, 4, 6, 8, 10};

        for (int i = 0; i < numbers.length; i++) {
            System.out.println("Element at index " + i + ": " + numbers[i]);
        }
    }
}

Output:

Element at index 0: 2  
Element at index 1: 4  
Element at index 2: 6  
Element at index 3: 8  
Element at index 4: 10

Example 4: Nested For Loop

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:

i: 1, j: 1  
i: 1, j: 2  
i: 1, j: 3  
i: 2, j: 1  
i: 2, j: 2  
i: 2, j: 3  
i: 3, j: 1  
i: 3, j: 2  
i: 3, j: 3

Enhanced For Loop (For-Each Loop)

Java also provides an enhanced for loop, known as the for-each loop, which is specifically designed for iterating over collections and arrays.

Syntax of For-Each Loop

for (type variable : array) {
    // Code to execute for each element
}

Example: Iterating Over an Array

public class ForEachExample {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3, 4, 5};

        for (int num : numbers) {
            System.out.println("Number: " + num);
        }
    }
}

Output:

Number: 1  
Number: 2  
Number: 3  
Number: 4  
Number: 5

Common Mistakes and How to Avoid Them

1. Infinite Loops:
   • Always ensure the condition will eventually evaluate to false.
2. Off-by-One Errors:
   • Carefully plan the starting and ending points of your loop to avoid iterating one extra or one fewer time.
3. Incorrect Updates:
   • Ensure that the loop variable is updated appropriately within the loop to avoid logical errors.

Advantages of For Loop

1. Compact and Readable:
   • Combines initialization, condition, and update in one line.
2. Control Over Iterations:
   • Provides precise control over the number of iterations.
3. Flexibility:
   • Can be used for a variety of tasks, including simple iterations, complex calculations and nested operations.