Try It Yourself - SyntaxStudy Editor

HTML / CSS / JS

import java.util.List;

// Abstract base class
abstract class Shape {
    private String color;

Shape(String color) { this.color = color; }

public String getColor() { return color; }

// Abstract method — every concrete Shape must implement this
    public abstract double area();

// Concrete method — shared by all shapes
    public void describe() {
        System.out.printf("%s [color=%s, area=%.2f]%n",
            getClass().getSimpleName(), color, area());
    }
}

class Circle extends Shape {
    private final double radius;
    Circle(String color, double radius) { super(color); this.radius = radius; }

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

class Rectangle extends Shape {
    private final double width, height;
    Rectangle(String color, double width, double height) {
        super(color);
        this.width = width; this.height = height;
    }
    @Override public double area() { return width * height; }
}

class Triangle extends Shape {
    private final double base, height;
    Triangle(String color, double base, double height) {
        super(color);
        this.base = base; this.height = height;
    }
    @Override public double area() { return 0.5 * base * height; }
}

public class PolymorphismDemo {
    public static void main(String[] args) {
        List<Shape> shapes = List.of(
            new Circle("red", 5),
            new Rectangle("blue", 4, 6),
            new Triangle("green", 3, 8)
        );

double totalArea = 0;
        for (Shape s : shapes) {
            s.describe();               // dynamic dispatch — correct subtype called
            totalArea += s.area();
        }
        System.out.printf("Total area: %.2f%n", totalArea);
    }
}