Java for Loop

Java for Loop

In this tutorial, we will learn how to use for loop in Java with the help of examples and we will likewise find out about the working of Loop in computer programming.

In computer programming, loops are used to rehash a square of code. For instance, if you need to show a message multiple times, at that point as opposed to typing the similar code multiple times, you can use a loop.

In Java, there are three types of loops.

• for loop
• while loop
• do…while loop

This tutorial focuses on the for a loop. You will learn about the other type of loops in the upcoming tutorials.

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Java for Loop

Java for loop is used to run a block of code for a certain number of times. The syntax of for loop is:

for (initialExpression; testExpression; updateExpression) {
    // body of the loop
}

• Here, The initialExpression initializes and/or declares variables and executes only once.
• The condition is evaluated. If the condition is true, the body of the for loop is executed.
• The updateExpression updates the value of initialExpression.
• The condition is evaluated again. The process continues until the condition is false.

To learn more about the conditions, visit Java relational and logical operators.

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Example 1: Display a Text Five Times

// Program to print a text 5 times

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

    int n = 5;
    // for loop  
    for (int i = 1; i <= n; ++i) {
      System.out.println("Java is fun");
    }
  }
}

Output

Java is fun
Java is fun
Java is fun
Java is fun
Java is fun

Here is how this program works.

Iteration	Variable	Condition: i <= n	Action
1st	i = 1 n = 5	true	Java is fun is printed. i is increased to 2.
2nd	i = 2 n = 5	true	Java is fun is printed. i is increased to 3.
3rd	i = 3 n = 5	true	Java is fun is printed. i is increased to 4.
4th	i = 4 n = 5	true	Java is fun is printed. i is increased to 5.
5th	i = 5 n = 5	true	Java is fun is printed. i is increased to 6.
6th	i = 6 n = 5	false	The loop is terminated.

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Example 2: Display numbers from 1 to 5

// Program to print numbers from 1 to 5

class Main {
  public static void main(String[] args) {
  
    int n = 5;
    // for loop  
    for (int i = 1; i <= n; ++i) {
      System.out.println(i);
    }
  }
}

Output

1
2
3
4
5

Here is how the program works.

Iteration	Variable	Condition: i <= n	Action
1st	i = 1 n = 5	true	1 is printed. i is increased to 2.
2nd	i = 2 n = 5	true	2 is printed. i is increased to 3.
3rd	i = 3 n = 5	true	3 is printed. i is increased to 4.
4th	i = 4 n = 5	true	4 is printed. i is increased to 5.
5th	i = 5 n = 5	true	5 is printed. i is increased to 6.
6th	i = 6 n = 5	false	The loop is terminated.

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Example 3: Display Sum of n Natural Numbers

// Program to find the sum of natural numbers from 1 to 1000.

class Main {
  public static void main(String[] args) {
      
    int sum = 0;
    int n = 1000;

    // for loop
    for (int i = 1; i <= n; ++i) {
      // body inside for loop
      sum += i;     // sum = sum + i
    }
       
    System.out.println("Sum = " + sum);
  }
}

Output

Sum = 500500

Here, the value of the sum is 0 at first. At that point, the for loop is iterated from I = 1 to 1000. In every cycle, i is added to the sum and its worth is increased by 1.

When i becomes 1001, the test condition is false and sum will be equal to 0 + 1 + 2 + …. + 1000.

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The above program to include the sum of natural numbers can likewise be written as

// Program to find the sum of natural numbers from 1 to 1000.

class Main {
  public static void main(String[] args) {
      
    int sum = 0;
    int n = 1000;

    // for loop
    for (int i = n; i >= 1; --i) {
      // body inside for loop
      sum += i;     // sum = sum + i
    }
       
    System.out.println("Sum = " + sum);
  }
}

The output of this program is the same as the Example 3.

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Java for-each Loop

The Java for loop has an alternative syntax that makes it easy to iterate through arrays and collections. For example,

// print array elements 

class Main {
  public static void main(String[] args) {
      
    // create an array
    int[] numbers = {3, 7, 5, -5};
    
    // iterating through the array 
    for (int number: numbers) {
       System.out.println(number);
    }
  }
}

Output

3
4
5
-5

Here, we have used the for-each loop to print each element of the numbers array one by one.

In the first iteration of the loop, number will be 3, number will be 7 in second iteration and so on.

To learn more, visit Java for-each Loop.

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Java Infinite for Loop

Ift we set the test expression so that it never assesses to false, the for loop will run for eternity. This is called infinite for loop. For instance,

// Infinite for Loop

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

        for (int i = 1; i <= 10; --i) {
            System.out.println("Hello");
        }
    }
}

Here, the test expression ,i <= 10, is never false and Hello is printed repeatedly until the memory runs out.

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