Java If-Else Statement

The if-else statement is one of the most fundamental decision-making structures in programming. It allows your program to execute different code based on whether a condition is true or false. In Java, we use the if-else statement to control the flow of execution depending on certain conditions.

In this blog, we'll explore how the if-else statement works in Java, provide explanations, and demonstrate examples with expected outputs.

What is an If-Else Statement?#

An if-else statement is used to execute one block of code if a condition is true, and another block if the condition is false. It's a way to introduce logic in your program, so it can make decisions.

The syntax for an if-else statement in Java is:

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

Flow of Execution#

1. If condition: The condition inside the if is evaluated. If the condition is true, the block of code inside the if is executed.
2. Else block: If the condition is false, the block of code inside the else is executed.

Basic Example: If-Else Statement#

Let's start with a simple example to see how the if-else statement works.

Example 1: Basic If-Else Statement#

class Main {
  public static void main(String[] args) {
    int number = 10;

    // If-Else statement to check if number is positive or negative
    if (number > 0) {
      System.out.println("The number is positive.");
    } else {
      System.out.println("The number is negative.");
    }
  }
}

Explanation:

• The condition number > 0 is evaluated. Since the value of number is 10, which is greater than 0, the condition is true, and the code inside the if block is executed.
• If the number was negative or zero, the code inside the else block would have been executed.

Expected Output:

The number is positive.

If-Else with Multiple Conditions: Using else if#

Sometimes, we want to check for more than two conditions. In this case, we can use the else if statement to check additional conditions after the initial if condition.

Example 2: If-Else-If Statement#

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

    // If-Else-If statement to check if the number is positive, negative, or zero
    if (number > 0) {
      System.out.println("The number is positive.");
    } else if (number < 0) {
      System.out.println("The number is negative.");
    } else {
      System.out.println("The number is zero.");
    }
  }
}

Explanation:

• The first condition checks if the number is positive. Since the number is 0, it moves to the else if condition and checks if the number is negative.
• Finally, since the number is neither positive nor negative, the else block is executed, and the program prints "The number is zero."

Expected Output:

The number is zero.

Nested If-Else Statement#

A nested if-else statement is when you place an if-else statement inside another if or else block. This is useful when you have more complex conditions to check.

Example 3: Nested If-Else Statement#

class Main {
  public static void main(String[] args) {
    int age = 18;

    // Nested if-else to check voting eligibility
    if (age >= 18) {
      if (age == 18) {
        System.out.println("You are 18 years old and eligible to vote for the first time.");
      } else {
        System.out.println("You are eligible to vote.");
      }
    } else {
      System.out.println("You are not eligible to vote.");
    }
  }
}

Explanation:

• The first if checks if the age is greater than or equal to 18.
• Inside the if block, there's another if that checks if the age is exactly 18.
• If the age is 18, it prints a specific message for first-time voters. Otherwise, it simply prints that the person is eligible to vote.

Expected Output:

You are 18 years old and eligible to vote for the first time.

If-Else with Logical Operators#

You can also combine multiple conditions in an if statement using logical operators like && (AND), || (OR), and ! (NOT). This helps you to create more complex conditions.

Example 4: If-Else with Logical AND (&&)#

class Main {
  public static void main(String[] args) {
    int age = 25;
    boolean hasVoterID = true;

    // If-Else with logical AND (&&) to check voting eligibility
    if (age >= 18 && hasVoterID) {
      System.out.println("You are eligible to vote.");
    } else {
      System.out.println("You are not eligible to vote.");
    }
  }
}

Explanation:

• The condition age >= 18 && hasVoterID checks if both conditions are true. Since both are true in this case (age is 25 and the person has a voter ID), the if block is executed.

Expected Output:

You are eligible to vote.

Example 5: If-Else with Logical OR (||)#

class Main {
  public static void main(String[] args) {
    int age = 17;
    boolean hasParentalConsent = true;

    // If-Else with logical OR (||) to check voting eligibility with consent
    if (age >= 18 || hasParentalConsent) {
      System.out.println("You are eligible to vote.");
    } else {
      System.out.println("You are not eligible to vote.");
    }
  }
}

Explanation:

• The condition age >= 18 || hasParentalConsent checks if either the age is 18 or older or the person has parental consent.
• Since the person is 17 but has parental consent, the if block is executed.

Expected Output:

You are eligible to vote.

Conclusion#

In this blog, we've learned:

• The if-else statement allows you to make decisions in your program by checking conditions.
• The if-else structure can handle simple or multiple conditions using if, else if, and else.
• We can also use logical operators like && (AND) and || (OR) to combine multiple conditions.
• Nested if-else statements allow more complex logic.

Mastering the if-else statement is crucial for writing programs that make decisions based on data, and it’s a fundamental concept in programming. With these building blocks, you can create powerful decision-making logic in your Java applications.