Java for Loop

In this tutorial, we will learn how to use the for loop in Java with the help of examples.

Loops are used to repeat a block of code. For example, if we want to display a message 10 times, we can use a loop rather than typing the same code 10 times.

Java for Loop

Java for loop is used to repeat a specific block of code for a certain number of times.

The syntax of the Java for loop can be given as follows:

for(initialization; condition; updation) {
    // body of the loop 
}

Here,

• initializationExpression - It initializes or declares variables and executes only once.
• condition - The condition is evaluated. If it is true, the body of the for loop is executed.
• updateExpression - It updates the value of the initialization expression. It is executed every time after the code block has been executed.

The following example will print the numbers 0 to 5:

public class Main {
    public static void main(String[] args) {

        for(int i = 0; i < 6; i++) {
            System.out.println(i);
        }
    }
}

Output:

0
1
2
3
4
5

Example explained

• int i = 0 - It sets a variable before the loop starts.
• i < 6 - It defines the condition for the loop to run. If the condition is true, the loop will start over again. If it is false, the loop will end.
• i++ - It increases the value each time the code in the loop is being executed.

Flowchart of Java for Loop

The following illustration shows how the Java for loop works.

Example: Display a Text Three Times

In the following example, we will display a text three times.

public class Main {
    public static void main(String[] args) {
        
        int n = 3;
        for(int i = 0; i < n; ++i) {
            System.out.println("Hello World");
        }
    }
}

Output:

Hello World
Hello World
Hello World

Here is how the above program works.

Example: Calculate the Sum of n Natural Numbers

In the following example, we will calculate the sum of n natural numbers.

public class Main {
    public static void main(String[] args) {
        
        int sum = 0;
        int n = 500;

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

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

Output:

Sum = 125250

In the above program, the value of sum is initialized to 0. The for loop is iterated from i = 1 to 500. In each iteration, i is added to sum, and its value is increased by 1.

When i becomes 501, the test condition is false and sum will be equal to 0 + 1 + 2 + 3 + ... + 500.

Java for-each Loop

Java offers an alternative syntax of the for loop to make it easy to iterate through arrays and collections. For example,

public class Main {
    public static void main(String[] args) {
        
        // create an array
        int[]  numbArray = {17, 5, 28, 7, 43, 85};

        // using for-each to iterate though the array
        for(int numb : numbArray) {
            System.out.println(numb);
        }
    }
}

Output

17
5
28
7
43
85

Above, we have used the for-each loop to display each element of the numbArray array one element by one.

In the first iteration of the loop, numb will be 17, then 5 in the second iteration, and so on.

To learn more, you can visit Java for-each Loop

Java Infinite for Loop

In Java, creating an infinite loop can be made by setting the test condition in a way that it never evaluates to false. For example,

public class Main {
    public static void main(String[] args) {
        
        int sum = 0;
        
        for(int i = 0; i <= 5; --i) {
            System.out.println("Hello World");
        }
    }
}

In the above program, the test condition, i <= 5, is never false, and Hello World is printed repeatedly until the memory runs out.