Java Loops
  1. Introduction to Programming with Java
  2. Java Loops

Java Loops

If you want to print "Hello, World!" to the console 100 times without repeating the System.out.println("Hello, World!"); command, you can utilize loops in Java. A loop repeatedly executes a block of code until a specified termination condition is satisfied. Java provides the following types of loops:

1. for Loop

A for loop is used to execute a block of code a defined number of times. Its syntax is:

for (initialization; condition; update) {
    // Code block to be executed
}
  • initialization: This expression runs once at the beginning of the loop and is typically used to declare and initialize the loop control variable, for instance: int i = 0.
  • condition: This boolean expression is evaluated before each iteration. If it evaluates to true, the code block within the loop is executed; if it’s false, the loop ends. For example: i < 5.
  • update: This expression is executed after each iteration and usually updates the loop control variable. For example: i++.

Example

public class Main {

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

Output

Iteration 0 - Hello, World!
Iteration 1 - Hello, World!
Iteration 2 - Hello, World!
Iteration 3 - Hello, World!
Iteration 4 - Hello, World!

In the above program, the for loop operates as follows:

Iteration Explanation
1 The loop control variable i is initialized to 0, so its value is 0 during the first iteration. Since i is less than 5, the print statement runs. After executing the print statement and before the next iteration, i is incremented by 1, changing its value to 1.
2 i is currently 1. Since it is less than 5, the print statement is executed. Once the print statement is executed, i is incremented by 1 before the next iteration, bringing its value to 2.
3 - 5 Functions the same way as in the second iteration.
6 At this point, i is 5. Because it is not less than 5, the loop ends, and nothing is printed to the console.

2. while Loop

A while loop executes a block of code repeatedly as long as a specified condition remains true. Its syntax is:

while (condition) {
    // Code block to be executed
}
  • condition: This boolean expression is evaluated before each iteration. If it is true, the code inside the loop executes; if it is false, the loop stops.

Example

public class Main {

    public static void main(String[] args) {
        int i = 0;

        while (i < 5) {
            System.out.println("Iteration " + i + " - Hello, World!");
            i++;
        }
    }
}

Output

Iteration 0 - Hello, World!
Iteration 1 - Hello, World!
Iteration 2 - Hello, World!
Iteration 3 - Hello, World!
Iteration 4 - Hello, World!

In this program, the while loop works as follows:

Iteration Explanation
1 The loop control variable i is set to 0 before the while loop begins, so in the first iteration its value is 0. Since i is less than 5, the print statement is executed first, and then i is incremented to 1.
2 i is currently 1. Since it is less than 5, the print statement is executed, and then i is incremented by 1, bringing its value to 2.
3 - 5 Functions the same way as in the second iteration.
6 At this point, i is 5. Because it is not less than 5, the loop ends, and nothing is printed to the console.

3. do-while Loop

A do-while loop guarantees that a block of code runs at least once and continues to execute as long as a specified condition is true. This type of loop ensures the code executes at least once, even if the initial condition is false. Its syntax is:

do {
    // Code block to be executed
} while (condition);
  • condition: After executing the code block, the condition is checked. If it is true, the loop repeats; if it is false, the loop stops.

Example

public class Main {

    public static void main(String[] args) {
        int i = 0;

        do {
            System.out.println("Iteration " + i + " - Hello, World!");
            i++;
        } while (i < 0);
    }
}

Output

Iteration 0 - Hello, World!

In this program, the do-while loop operates as follows:

Iteration Explanation
1 The loop control variable i is initialized to 0 before the do-while loop starts, so it begins with a value of 0 in the first iteration. The print statement runs first, followed by incrementing i to 1. At this stage, the condition i < 0 is checked. Since it is false, the loop terminates.
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