Polymorphism: overloading and overriding

1 Learn

Polymorphism means "many forms": the same method name can behave differently.

Overloading: same method name in one class with different parameter lists. Java chooses at compile time.

Overriding: a subclass provides its own version of a parent method with the same signature. Java chooses at run time, based on the actual object.

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2 See the Code

Java

class Shape {
    void draw() { System.out.println("Drawing a shape"); }
}

class Circle extends Shape {
    @Override
    void draw() { System.out.println("Drawing a circle"); }
}

public class Art {
    static int area(int side) { return side * side; }
    static int area(int l, int w) { return l * w; }

    public static void main(String[] args) {
        System.out.println(area(4));
        System.out.println(area(3, 5));
        Shape s = new Circle();
        s.draw();
    }
}

area(int) and area(int, int) are overloaded.
Circle overrides draw(). Even though s is a Shape variable, the object is a Circle, so the Circle version runs.

Output

16
15
Drawing a circle

3 Practice

Overload a method greet() and greet(String name). Then override speak() in a Cat class.

Try it in your own Java setup or write it in the Practice Notebook.

4 Quick Check

1. Overloading means...
2. Shape s = new Circle(); s.draw(); runs whose draw?

Step 5

Answer and check the Quick Check above to unlock this.

Day 19