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If-else Statement in Java

  • An if-else statement extends the basic if statement to provide an alternative block of code to execute when the condition is false.

  • Essentially, it tells your program: "If this condition is true, do this; otherwise, do that."

  • This control flow structure allows your program to choose between two blocks of code based on a condition.

Syntax of an if-else Statement​

Here is the basic syntax of an if-else statement in Java:

if (condition) {
    // code to be executed if the condition is true
} else {
    // code to be executed if the condition is false
}

  • condition: A boolean expression (an expression that evaluates to either true or false).

  • code block (if): The set of statements that will be executed if the condition is true.

  • code block (else): The set of statements that will be executed if the condition is false.

How It Works​

When an if-else statement is encountered, the condition inside the parentheses is evaluated:

  • If the condition is true, the code block inside the first set of curly braces {} is executed.

  • If the condition is false, the code block inside the else set of curly braces {} is executed.

Example of an if-else Statement​

Let's look at a simple example to understand how an if-else statement works. Consider the following code:

public class Main {
    public static void main(String[] args) {
        int number = -5;

        if (number > 0) {
            System.out.println("The number is positive.");
        } else {
            System.out.println("The number is not positive.");
        }
    }
}

Explanation:​

  • Declaration of the variable: We declare an integer variable number and assign it a value of -5.

  • The if statement: We check if number is greater than 0 using the condition number > 0.

  • Code block (if): If the condition is true, the code inside the first set of curly braces {} will execute, printing "The number is positive."

  • Code block (else): If the condition is false, the code inside the else set of curly braces {} will execute, printing "The number is not positive."

Since number is -5 (which is not greater than 0), the condition is false, and the output will be:

The number is not positive.

Summary​

  • if-else statement: Executes one block of code if a condition is true and another block of code if the condition is false.

  • Condition: A boolean expression that determines which code block will be executed.

  • Code blocks: The statements that run depending on whether the condition is true or false, enclosed in curly braces {}.

The if-else statement is a powerful tool for making decisions in your Java programs.