How to use polymorphism to make list with different types in java?

Question

I have 3 Classes Circle, Rectangle and Square

I want to get required data for each of above classes and create them by user .

It me

Answer 1

You can define an interface and all your classes will implement this interface. Add all common methods into an interface.

public interface Shapes {
   public double calculateArea();
   public double calculatePrimeter();
}

Now all your shape class's will implement the above interface and provide implementation to interface methods. In your case change the return type of all your methods. you can keep it double.

public class Circle implements Shapes{
    private int radius;

    public Circle (int radius) {
        this.radius = radius;
    }

    @Override
    public double calculateArea() {
        return (radius * radius) * Math.PI;
    }

    @Override
    public double calculatePrimeter() {
        return (radius * 2) * Math.PI;
    }
}

public class Rectangle implements Shapes{}
public class Square implements Shapes{}

Then you need to have one list

static List unitList = new ArrayList();

Get inputs from the user & add to the above list. Then simply loop unitList & call respective methods

For calculating Area

for (Shapes shape : unitList)
    System.out.println("Area: " + shape.calculateArea());

For calculating Perimeter

for (Shapes shape : unitList)
    System.out.println("Perimeter: " + shape.calculatePrimeter());