Java For Loop

What is a For Loop?

A for loop repeats a block of code a known number of times. It's the most commonly used loop when you know in advance how many iterations are needed.

java

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

Part	Purpose	Example
Initialization	Set up loop variable	`int i = 0`
Condition	Check before each iteration	`i < 10`
Update	Execute after each iteration	`i++`

Basic For Loop

java

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

Output:

Iteration: 1
Iteration: 2
Iteration: 3
Iteration: 4
Iteration: 5

How it executes step by step:

Step	`i`	Condition `i <= 5`	Action
1	1	true	Print, then `i++`
2	2	true	Print, then `i++`
3	3	true	Print, then `i++`
4	4	true	Print, then `i++`
5	5	true	Print, then `i++`
6	6	false	Loop ends

Common For Loop Patterns

Counting Forward

java

// 1 to 10
for (int i = 1; i <= 10; i++) {
    System.out.print(i + " ");
}
// Output: 1 2 3 4 5 6 7 8 9 10

Counting Backward

java

// 10 to 1
for (int i = 10; i >= 1; i--) {
    System.out.print(i + " ");
}
// Output: 10 9 8 7 6 5 4 3 2 1

Stepping by 2 (Even Numbers)

java

for (int i = 2; i <= 20; i += 2) {
    System.out.print(i + " ");
}
// Output: 2 4 6 8 10 12 14 16 18 20

Iterating Over an Array

java

int[] scores = {85, 92, 78, 95, 88};

for (int i = 0; i < scores.length; i++) {
    System.out.println("Student " + (i + 1) + ": " + scores[i]);
}

Output:

Student 1: 85
Student 2: 92
Student 3: 78
Student 4: 95
Student 5: 88

Enhanced For Loop (For-Each)

The for-each loop simplifies iterating over arrays and collections when you don't need the index:

java

// Syntax: for (dataType element : collection) { }

String[] fruits = {"Apple", "Mango", "Banana", "Grapes"};

for (String fruit : fruits) {
    System.out.println("I like " + fruit);
}

Output:

I like Apple
I like Mango
I like Banana
I like Grapes

For Loop vs For-Each

java

int[] numbers = {10, 20, 30, 40, 50};

// Traditional for — when you need the index
for (int i = 0; i < numbers.length; i++) {
    System.out.println("Index " + i + ": " + numbers[i]);
}

// For-each — when you only need the value
for (int num : numbers) {
    System.out.println("Value: " + num);
}

Feature	`for` loop	`for-each` loop
Access index	✓ Yes	✗ No
Modify elements	✓ Yes	✗ No (copy only)
Cleaner syntax	—	✓ Yes
Use with Collections	✓ Yes	✓ Yes

Nested For Loops

A loop inside another loop. The inner loop runs completely for each iteration of the outer loop.

Multiplication Table

java

public class MultiplicationTable {
    public static void main(String[] args) {
        for (int i = 1; i <= 5; i++) {
            for (int j = 1; j <= 10; j++) {
                System.out.printf("%4d", i * j);
            }
            System.out.println();
        }
    }
}

Output:

   1   2   3   4   5   6   7   8   9  10
   2   4   6   8  10  12  14  16  18  20
   3   6   9  12  15  18  21  24  27  30
   4   8  12  16  20  24  28  32  36  40
   5  10  15  20  25  30  35  40  45  50

Star Pattern

java

public class StarPattern {
    public static void main(String[] args) {
        int rows = 5;

        for (int i = 1; i <= rows; i++) {
            for (int j = 1; j <= i; j++) {
                System.out.print("* ");
            }
            System.out.println();
        }
    }
}

Output:

*
* *
* * *
* * * *
* * * * *

Loop Control: break and continue

`break` — Exit the Loop Early

java

// Find the first negative number
int[] numbers = {5, 12, -3, 8, -7, 15};

for (int i = 0; i < numbers.length; i++) {
    if (numbers[i] < 0) {
        System.out.println("First negative number: " + numbers[i] + " at index " + i);
        break;  // Stop the loop immediately
    }
}

Output:

First negative number: -3 at index 2

`continue` — Skip Current Iteration

java

// Print only even numbers
for (int i = 1; i <= 10; i++) {
    if (i % 2 != 0) {
        continue;  // Skip odd numbers
    }
    System.out.print(i + " ");
}
// Output: 2 4 6 8 10

Labeled Break (for Nested Loops)

java

outer:
for (int i = 1; i <= 3; i++) {
    for (int j = 1; j <= 3; j++) {
        if (i == 2 && j == 2) {
            break outer;  // Breaks out of BOTH loops
        }
        System.out.println("i=" + i + ", j=" + j);
    }
}

Output:

i=1, j=1
i=1, j=2
i=1, j=3
i=2, j=1

Infinite For Loop

A loop without a condition runs forever (use with caution):

java

// Intentional infinite loop (e.g., game loop, server)
for (;;) {
    System.out.println("Running...");
    // Must have a break condition!
    break;
}

Practical Example: Student Report Card

java

import java.util.Scanner;

public class ReportCard {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String[] subjects = {"Mathematics", "Physics", "Chemistry", "English", "Computer Science"};
        int[] marks = new int[subjects.length];
        int total = 0;

        // Input marks
        System.out.println("=== Enter Marks (out of 100) ===");
        for (int i = 0; i < subjects.length; i++) {
            System.out.print(subjects[i] + ": ");
            marks[i] = scanner.nextInt();
            total += marks[i];
        }

        // Display report
        System.out.println("\n=== Report Card ===");
        System.out.printf("%-20s %s%n", "Subject", "Marks");
        System.out.println("─".repeat(30));

        for (int i = 0; i < subjects.length; i++) {
            String status = (marks[i] >= 40) ? "Pass" : "Fail";
            System.out.printf("%-20s %d (%s)%n", subjects[i], marks[i], status);
        }

        System.out.println("─".repeat(30));
        double percentage = (double) total / (subjects.length * 100) * 100;
        System.out.printf("Total: %d / %d%n", total, subjects.length * 100);
        System.out.printf("Percentage: %.1f%%%n", percentage);

        // Determine grade using for loop
        String[] grades = {"A+", "A", "B", "C", "D", "F"};
        int[] cutoffs = {90, 80, 70, 60, 50, 0};
        String grade = "F";

        for (int i = 0; i < cutoffs.length; i++) {
            if (percentage >= cutoffs[i]) {
                grade = grades[i];
                break;
            }
        }

        System.out.println("Grade: " + grade);
        scanner.close();
    }
}

Sample Output:

=== Enter Marks (out of 100) ===
Mathematics: 85
Physics: 78
Chemistry: 92
English: 88
Computer Science: 95

=== Report Card ===
Subject              Marks
──────────────────────────────
Mathematics          85 (Pass)
Physics              78 (Pass)
Chemistry            92 (Pass)
English              88 (Pass)
Computer Science     95 (Pass)
──────────────────────────────
Total: 438 / 500
Percentage: 87.6%
Grade: A

Summary

The for loop has three parts: initialization, condition, and update
Use the for-each loop for simple iteration over arrays and collections
Nested loops run the inner loop completely for each outer iteration
break exits the loop early; continue skips to the next iteration
Use labeled break to exit outer loops from nested loops
The for loop is ideal when the number of iterations is known in advance
Always ensure the loop condition will eventually become false to avoid infinite loops

What is a For Loop?

Basic For Loop

How it executes step by step:

Common For Loop Patterns

Counting Forward

Counting Backward

Stepping by 2 (Even Numbers)

Iterating Over an Array

Enhanced For Loop (For-Each)

For Loop vs For-Each

Nested For Loops

Multiplication Table

Star Pattern

Loop Control: break and continue

break — Exit the Loop Early

continue — Skip Current Iteration

Labeled Break (for Nested Loops)

Infinite For Loop

Practical Example: Student Report Card

Summary

`break` — Exit the Loop Early

`continue` — Skip Current Iteration