Method Overrides

Every class inherits methods from its parent class. These methods can be called in the child class and can also be overridden.

public class Shape {
    protected String name;
    private int length;
    private int width;

    // Default constructor
    public Shape() {
        this.name = "rectangle";
        this.length = 10;
        this.width = 5;
    }

    // Parameterized constructor
    public Shape(String name, int length, int width) {
        this.name = name;
        this.length = length;
        this.width = width;
    }

    // Getter methods
    public String get_name() {
        return this.name;
    }

    public int get_length() {
        return this.length;
    }

    public int get_width() {
        return this.width;
    }

    // Setter methods
    public void set_name(String n) {
        this.name = n;
    }

    public void set_length(int a) {
        this.length = a;
    }

    public void set_width(int b) {
        this.width = b;
    }

    // Method to calculate the area
    public double calc_area() {
        return this.length * this.width;
    }

    // Method to print the shape
    public void print_shape() {
        System.out.println("Shape: " + this.name);
    }

    // Additional method to print something
    public void print_something() {
        System.out.println("This is a shape");
    }
}

public class Driver {
    public static void main(String[] args) {
        Shape s1 = new Shape();
    }
}

// Run the driver code
Driver.main(new String[0]);

Creating a Triangle:

Currently Our shape class only takes in length and width parameters. This works fine for squares and rectangles, but what if we wanted to make a different shape? To define a Triangle we can use the 3 side lengths. while still inheriting the same behavior from the base Shape class.

public class Triangle extends Shape {
    private int side1;
    private int side2;
    private int side3;


    public Triangle() {
        this.name = "triangle";
        this.side1 = 1;
        this.side2 = 2;
        this.side3 = 3;
    }

    // Constructor that takes a name and three side lengths
    public Triangle(String name, int s1, int s2, int s3) {
        super(name, 0, 0); // Call to Shape constructor to set the name
        this.name = "triangle";
        this.side1 = s1;
        this.side2 = s2;
        this.side3 = s3;
    }

    @Override
    public double calc_area() {
        double s = (side1 + side2 + side3) / 2.0; // Semi-perimeter
        return Math.sqrt(s * (s - side1) * (s - side2) * (s - side3));
    }

    @Override
    public void print_something() {
        System.out.println("This is a Triangle");
    }
}


public class Driver {
    public static void main(String[] args) {
        Triangle t1 = new Triangle("triangle", 3, 3, 3);
        System.out.println("Area of t1 = " + t1.calc_area());

    }
}

// Run the driver code
Driver.main(new String[0]);

Area of t1 = 3.897114317029974

Here’s our Triangle

As seen above, we’re creating a new child class: Triangle This class inherits name paramiter from the parent shape class and takes in 3 new side length paramiters to define the triangle’s geometry.