OBJECT ORIENTED PROGRAMMING THROUGH JAVA : Unit - 2 : Topic - 11 : Introducing Methods in Java

Unit - 2

Topic - 11 :Introducing Methods in Java

In Java, a method is a block of code that performs a specific task.
Methods make programs modular, reusable, and easy to maintain.

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General Form of a Method

type name(parameter-list) {
    // body of method
}

Where:

• type → The data type of the value returned by the method.

  • Can be any valid type, including custom class types.

  • If no value is returned, use void.

• name → The name of the method (must be a valid identifier).

• parameter-list → A list of parameters (type and variable name), separated by commas.

  • If no parameters are needed, leave it empty.

• return value; → Used to send a value back to the caller (for non-void methods).

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Example 1: Method Without Return Value

Here, the method volume() computes and displays the volume of a box directly.

class Box {
    double width;
    double height;
    double depth;

    // Method to display volume
    void volume() {
        System.out.print("Volume is ");
        System.out.println(width * height * depth);
    }
}

class BoxDemo3 {
    public static void main(String args[]) {
        Box mybox1 = new Box();
        Box mybox2 = new Box();

        // Assign values to mybox1
        mybox1.width = 10;
        mybox1.height = 20;
        mybox1.depth = 15;

        // Assign values to mybox2
        mybox2.width = 3;
        mybox2.height = 6;
        mybox2.depth = 9;

        // Display volumes
        mybox1.volume();
        mybox2.volume();
    }
}

Output:

Volume is 3000.0
Volume is 162.0

💡 Note: This method prints the volume directly, which means it cannot be used for calculations elsewhere.

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Example 2: Method with Return Value

This improved version of volume() returns the computed value so it can be used anywhere.

class Box {
    double width;
    double height;
    double depth;

    // Method to compute and return volume
    double volume() {
        return width * height * depth;
    }
}

class BoxDemo4 {
    public static void main(String args[]) {
        Box mybox1 = new Box();
        Box mybox2 = new Box();
        double vol;

        // Assign values to mybox1
        mybox1.width = 10;
        mybox1.height = 20;
        mybox1.depth = 15;

        // Assign values to mybox2
        mybox2.width = 3;
        mybox2.height = 6;
        mybox2.depth = 9;

        // Get and display volume of first box
        vol = mybox1.volume();
        System.out.println("Volume is " + vol);

        // Get and display volume of second box
        vol = mybox2.volume();
        System.out.println("Volume is " + vol);
    }
}

Output:

Volume is 3000.0
Volume is 162.0

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Key Points

• Void methods → Perform an action but do not return a value.

• Return type methods → Return computed values for further use.

• Modularity → Methods make code organized and reusable.

• Parameters → Allow passing different values to a method, making it more flexible.