Khalid Ahmad Khattak

Lesson 9 – Methods

Methods are blocks of code that perform a specific task. They make your programs organised, reusable, and easier to understand.

Why Use Methods?

• Reduce repetition
• Break programs into smaller parts
• Improve readability
• Reuse code anywhere in the program

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1. Creating Your First Method

public class Main {
    static void greet() {
        System.out.println("Hello! Welcome to Java.");
    }

    public static void main(String[] args) {
        greet();  // calling the method
    }
}
        

static void greet() means:

• static → method belongs to the class
• void → method returns nothing
• greet → method name

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2. Method With Parameters

public class Main {
    static void greet(String name) {
        System.out.println("Hello " + name + "!");
    }

    public static void main(String[] args) {
        greet("Khalid");
        greet("Ali");
        greet("Sara");
    }
}
        

This method takes a String input and uses it inside the method.

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3. Method With Two Parameters

public class Main {
    static void printSum(int a, int b) {
        System.out.println("Sum = " + (a + b));
    }

    public static void main(String[] args) {
        printSum(5, 3);
        printSum(10, 20);
        printSum(100, 250);
    }
}
        

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4. Methods That Return a Value

public class Main {
    static int square(int number) {
        return number * number;
    }

    public static void main(String[] args) {
        int result = square(6);
        System.out.println("Square = " + result);
    }
}
        

Example 2 – Return Full Name

public class Main {
    static String fullName(String first, String last) {
        return first + " " + last;
    }

    public static void main(String[] args) {
        String name = fullName("Khalid", "Khattak");
        System.out.println(name);
    }
}
        

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5. Methods With If–Else Logic

public class Main {
    static String checkAge(int age) {
        if (age >= 18) {
            return "Adult";
        } else {
            return "Minor";
        }
    }

    public static void main(String[] args) {
        System.out.println(checkAge(15));
        System.out.println(checkAge(21));
    }
}
        

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6. Using Loops Inside Methods

Example – Print numbers from 1 to n

public class Main {
    static void printNumbers(int n) {
        for (int i = 1; i <= n; i++) {
            System.out.println(i);
        }
    }

    public static void main(String[] args) {
        printNumbers(5);
        printNumbers(10);
    }
}
        

Example – Return sum of numbers 1 to n

public class Main {
    static int sumToN(int n) {
        int total = 0;
        for (int i = 1; i <= n; i++) {
            total += i;
        }
        return total;
    }

    public static void main(String[] args) {
        System.out.println(sumToN(5));   // 15
        System.out.println(sumToN(10));  // 55
    }
}
        

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7. Calling One Method From Another

public class Main {

    static int add(int a, int b) {
        return a + b;
    }

    static void printDoubleSum(int x, int y) {
        int result = add(x, y);
        System.out.println("Double of the sum = " + (result * 2));
    }

    public static void main(String[] args) {
        printDoubleSum(4, 6);
    }
}
        

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8. Real-World Example – Calculator Functions

public class Main {

    static int add(int a, int b) {
        return a + b;
    }

    static int subtract(int a, int b) {
        return a - b;
    }

    static int multiply(int a, int b) {
        return a * b;
    }

    static double divide(int a, int b) {
        return (double)a / b;
    }

    public static void main(String[] args) {
        System.out.println(add(5, 2));
        System.out.println(subtract(10, 3));
        System.out.println(multiply(4, 6));
        System.out.println(divide(9, 2));
    }
}
        

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Summary

• A method is a block of code that performs a task
• Use parameters to give data to methods
• Use return to get data back
• Methods help reuse code and organise programs

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