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Java For Loop - Syntax, Flowchart and Examples

⏱️ 7 min read • Beginner Level • Lesson 28

Lesson 28 of 124 of Java Tutorial
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The for loop in Java is used to execute a block of code repeatedly for a specific number of times. It is commonly used when the number of iterations is already known.

Before learning the for loop, you should understand Java while loop, Java do-while loop, and Java operators.

On this page:

What is For Loop in Java?

A for loop is a repetition control structure that allows you to write a loop compactly. It is mostly used when you know how many times a statement or block of statements should execute.

  • A for loop is best for counter-based repetition.

  • Initialization, condition, and update are written in one line.

  • It is commonly used for printing patterns, tables, arrays, and repeated tasks.

Syntax of for Loop

A for loop has three main parts: initialization, condition, and update.

ForLoopSyntax.java
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for (initialization; condition; update) {
    // loop body
}
Note: The initialization runs once, the condition is checked before every iteration, and the update runs after each iteration.

Flowchart of for Loop

The following diagram shows how a for loop works. Java initializes the loop variable, checks the condition, executes the loop body, updates the variable, and then repeats.

Java for loop flowchart

How does it work?

  • Java first executes the initialization statement.
  • Then it checks the loop condition.
  • If the condition is true, the loop body executes.
  • After the loop body, the update statement executes.
  • The condition is checked again before the next iteration.
  • When the condition becomes false, the loop stops.

Real-World Uses of for Loop

  • Printing multiplication tables.
  • Processing arrays and collections.
  • Generating reports.
  • Creating patterns and shapes.
  • Repeating a task a fixed number of times.

Java for Loop Example

The following program prints Hello five times using a for loop.

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

Output:

1. Hello
2. Hello
3. Hello
4. Hello
5. Hello

Explanation

  1. The variable i is initialized with value 1.
  2. The condition i <= 5 is checked before each iteration.
  3. If the condition is true, the loop body prints the value of i with Hello.
  4. After each iteration, i++ increases the value of i by 1.
  5. When i becomes 6, the condition becomes false and the loop stops.

Example: Sum of First 5 Numbers

The following program calculates the sum of numbers from 1 to 5.

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

        for (int i = 1; i <= 5; i++) {
            sum = sum + i;
        }

        System.out.println("Sum = " + sum);
    }
}

Output:

Sum = 15

Example: Reverse Counting using for Loop

A for loop can also count backward by using a decrement operation.

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

Output:

5
4
3
2
1

Example: Factorial using for Loop

FactorialExample.java
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public class FactorialExample {
    public static void main(String[] args) {

        int number = 5;
        int factorial = 1;

        for(int i = 1; i <= number; i++) {
            factorial = factorial * i;
        }

        System.out.println("Factorial of " + number + " = " + factorial);
    }
}

Output:

Factorial of 5 = 120

Explanation of Factorial using for Loop

  1. The variable number stores the number whose factorial needs to be calculated.
  2. The variable factorial is initialized to 1 because factorial calculation starts with multiplication by 1.
  3. The for loop starts from i = 1 and runs until i <= number.
  4. During each iteration, the current value of factorial is multiplied by i.
  5. For number = 5, the calculations are:
    1 × 1 = 1
    1 × 2 = 2
    2 × 3 = 6
    6 × 4 = 24
    24 × 5 = 120
  6. After the loop finishes, the final value of factorial becomes 120.
  7. The program then displays: Factorial of 5 = 120.
Note:

A factorial is the product of all positive integers from 1 to the given number. For example, 5! = 5 × 4 × 3 × 2 × 1 = 120.

Example: Multiplication Table using for Loop

The following program prints the multiplication table of 5.

MultiplicationTable.java
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public class MultiplicationTable {
    public static void main(String[] args) {
        int number = 5;

        for (int i = 1; i <= 10; i++) {
            System.out.println(number + " x " + i + " = " + (number * i));
        }
    }
}

Output:

5 x 1 = 5
5 x 2 = 10
5 x 3 = 15
5 x 4 = 20
5 x 5 = 25
5 x 6 = 30
5 x 7 = 35
5 x 8 = 40
5 x 9 = 45
5 x 10 = 50

Nested for Loop Preview

A for loop can be placed inside another for loop. This is called a nested for loop and is commonly used for patterns, tables, and matrix operations.

NestedLoopPreview.java
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for(int row = 1; row <= 3; row++) {
    for(int col = 1; col <= 3; col++) {
        System.out.print("* ");
    }
    System.out.println();
}

Output:

* * *
* * *
* * *

Infinite for Loop

An infinite for loop happens when the condition never becomes false. Java also allows all three parts of a for loop to be omitted.

InfiniteForLoop.java
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public class InfiniteForLoop {
    public static void main(String[] args) {
        for (;;) {
            System.out.println("This loop runs forever");
        }
    }
}
Important: Infinite loops should be used carefully. In normal programs, make sure the loop condition eventually becomes false.

Difference Between for Loop and while Loop

for Loop while Loop
Best when the number of iterations is known. Best when the number of iterations is not known.
Initialization, condition, and update are written in one place. Initialization, condition, and update are usually written separately.
Commonly used for counters, arrays, and tables. Commonly used for condition-based repetition.

Common Mistakes in for Loop

  • Forgetting to update the loop variable.
  • Writing a condition that never becomes false.
  • Using incorrect comparison operators.
  • Adding an unwanted semicolon after the for statement.
  • Changing the loop variable incorrectly inside the loop body.
Interview Question:

When should you use a for loop instead of a while loop?

Use a for loop when the number of iterations is known in advance. Use a while loop when the number of iterations depends on a condition.

Summary:
  • The for loop is used to repeat code a fixed number of times.
  • It contains initialization, condition, and update in one line.
  • The condition is checked before each iteration.
  • It is useful for counting, tables, arrays, and repeated tasks.
  • An infinite for loop can be written as for (;;).

Interview Questions ⭐

A for loop in Java is used to execute a block of code repeatedly for a specific number of times.

A for loop is commonly used when the number of iterations is known in advance.

The three parts of a for loop are initialization, condition, and update.

Yes, a for loop can become infinite if the condition never becomes false or if all three parts are omitted like for (;;).

A for loop is usually used when the number of iterations is known, while a while loop is usually used when the number of iterations is not known.

Next step: Learn Java for-each Loop

🚀 Continue to Java for-each Loop →

🧠 Test your understanding with a quick quiz

🚀 Quick Knowledge Check

Topic: For-loop | Language: Java

Question 1 of 10
Q1. Which syntax creates an infinite for loop?
Q2. What is a common mistake in a for loop?
Q3. What is the output of this code?
for (int i = 5; i >= 1; i--) {
    System.out.println(i);
}
Q4. When is a for loop usually preferred over a while loop?
Q5. How many times will this loop execute?
for (int i = 1; i <= 5; i++) {
    System.out.println("Hello");
}
Q6. What is the main purpose of a for loop in Java?
Q7. Which are the three main parts of a for loop?
Q8. What will be the output of this code?
for (int i = 1; i <= 3; i++) {
    System.out.println(i);
}
Q9. What does the update expression do in a for loop?
Q10. Which statement is true about the initialization part of a for loop?

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