设计一条描述多边形的类型系统

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public abstract class Shape {
    protected int width;
    protected int height;

    public Shape(int width, int height) {
        this.width = width;
        this.height = height;
    }
    abstract double area();

}

public class Rectangle extends Shape{
    public Rectangle(int width, int height) {
        super(width, height);
    }

    @Override
    double area() {
        return width*height;
    }
    public void fill(String color){
        System.out.println("长方形为"+color);
    }
}