How to write Java if-else Statements

In Java, if-else statements are used to control the flow of a program based on certain conditions. The if statement executes a block of code if a condition evaluates to true. The else statement can follow an if and provides an alternative block of code to execute if the condition is false.

1. The Basic if Statement

The if statement allows you to execute a block of code only if a certain condition is true.

Syntax:

if (condition) {
    // Code to execute if the condition is true
}

Example:

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

        if (x > 5) {
            System.out.println("x is greater than 5");  // Outputs: x is greater than 5
        }
    }
}

In this example, the condition x > 5 is true, so the code inside the if block is executed.

2. The else Statement

The else statement follows an if and provides a block of code that runs if the if condition evaluates to false.

Syntax:

if (condition) {
    // Code to execute if the condition is true
} else {
    // Code to execute if the condition is false
}

Example:

public class Main {
    public static void main(String[] args) {
        int x = 3;

        if (x > 5) {
            System.out.println("x is greater than 5");
        } else {
            System.out.println("x is not greater than 5");  // Outputs: x is not greater than 5
        }
    }
}

In this example, since x > 5 is false, the code inside the else block is executed.

3. The else if Statement

The else if statement allows you to test multiple conditions. If the first if condition is false, it moves on to check the next else if condition. You can use multiple else if statements, and an optional else statement can be added at the end.

Syntax:

if (condition1) {
    // Code to execute if condition1 is true
} else if (condition2) {
    // Code to execute if condition2 is true
} else {
    // Code to execute if both conditions are false
}

Example:

public class Main {
    public static void main(String[] args) {
        int x = 7;

        if (x > 10) {
            System.out.println("x is greater than 10");
        } else if (x > 5) {
            System.out.println("x is greater than 5 but less than or equal to 10");  // Outputs this
        } else {
            System.out.println("x is 5 or less");
        }
    }
}

Here, since x is 7, the first condition is false, and the second else if condition (x > 5) is true, so the second block of code is executed.

4. Nested if Statements

You can nest if-else statements within each other to check multiple conditions. A nested if statement means placing an if or else if statement inside another if or else block.

Example:

public class Main {
    public static void main(String[] args) {
        int x = 10;
        int y = 20;

        if (x == 10) {
            if (y == 20) {
                System.out.println("x is 10 and y is 20");  // Outputs this
            }
        }
    }
}

In this example, both conditions are true, so the innermost if block is executed.

5. Ternary Operator

Java also provides a shorthand for if-else statements called the ternary operator. This operator allows you to write a concise if-else statement in a single line.

Syntax:

variable = (condition) ? expressionIfTrue : expressionIfFalse;

Example:

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

        String result = (x > 5) ? "x is greater than 5" : "x is not greater than 5";
        System.out.println(result);  // Outputs: x is greater than 5
    }
}

Here, the condition x > 5 is true, so the expression "x is greater than 5" is assigned to result and printed.

6. Boolean Expressions in if-else

Conditions in if-else statements are typically Boolean expressions. A Boolean expression is one that evaluates to true or false, using comparison or logical operators like ==, >, <, &&, ||, etc.

Example:

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

        if (age >= 18 && age < 65) {
            System.out.println("You are an adult");  // Outputs: You are an adult
        } else {
            System.out.println("You are not an adult");
        }
    }
}

Here, the condition age >= 18 && age < 65 is true, so the first block of code runs.

7. Common Mistakes

• Missing Braces: Although you can omit curly braces {} for single-line statements, it’s good practice to always use them to avoid errors.

// Without braces
if (x > 5)
    System.out.println("x is greater than 5");  // Works fine for single line

// With braces (Best practice)
if (x > 5) {
    System.out.println("x is greater than 5");
}

• Using = Instead of ==: Don’t confuse the assignment operator (=) with the equality operator (==).

if (x == 5) {   // Correct (checking equality)
    // Code here
}

Summary

• The if statement checks if a condition is true and executes a block of code.
• The else statement provides an alternative code block to execute if the if condition is false.
• The else if statement lets you check multiple conditions.
• Ternary operators allow you to write compact if-else statements.
• Boolean expressions, comparison operators, and logical operators are commonly used in if-else conditions.