java/w4/ShapeUtil.java

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 height;
	public Rectangle(double length,double height){
		this.length=length;
		this.height=height;
	}
	@Override
	public double getArea(){
		return length*height;
	}
}

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;
	}
}

public class ShapeUtil{
	public static void printArea(Shape shape){
		System.out.printf("ĂćťýĘÇ%.2f%n",shape.getArea());
	}
	public static void main(String[] args){
	Shape circle = new Circle(5.0);
	Shape rectangle = new Rectangle(10.0,20.0);
	Shape triangle = new Triangle(3.0,4.0);
	printArea(circle);
	printArea(rectangle);
	printArea(triangle);
	}
}