java/w4/Shape.java

package learn;

public abstract class Shape {
    public abstract double getArea();
}
class Circle extends Shape{
    private double radius;
    public Circle(double radius){
        this.radius=radius;
    }
    @Override
    public double getArea(){
        return Math.PI*radius*radius;
    }
}
class Rectangle extends Shape{
    private double length;
    private double width;
    public Rectangle(double length,double width){
        this.length=length;
        this.width=width;
    }
    @Override
    public double getArea(){
        return length*width;
    }
}
class Triangle extends Shape{
    private double base;
    private double height;
    public Triangle(double base,double height){
        this.base=base;
        this.height=height;
    }
    @Override
    public double getArea(){
        return base*height/2;
    }
}