ex3.java

讲述各种各样的java初始编程 了解编程

/*
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package chenchao3;


import java.util.ArrayList;


/**
 *
 * @author williechen
 */
public class Ex3 {
    ArrayList<Shape> shapes = new ArrayList<Shape>();

    public Ex3() {
        Rectangle rect = new Rectangle(3, 4);
        Circle circle = new Circle(3);
        Triangle tri = new Triangle(3,4,5);
       
        shapes.add(rect);
        shapes.add(circle); 
        shapes.add(tri);
   
    }
    
    public void test(){
        for(Shape s : shapes)
        {
            System.out.println(s.getClass().getName());
            System.out.println("Area is :" + s.area());
            System.out.println("Length is :" + s.circumference());
        }
    }
    
    public static void main(String[] args) {
        Ex3 test = new Ex3();
        test.test();
    }

}
abstract class Shape {

    public abstract double area();            // Abstract methods: note

    public abstract double circumference();   // semicolon instead of body. 
}

class Circle extends Shape {

    public static final double PI = 3.14159265358979323846;
    protected double r;                              // Instance data

    public Circle(double r) {
        this.r = r;
    }          // Constructor

    public double getRadius() {
        return r;
    }          // Accessor

    public double area() {
        return PI * r * r;
    }          // Implementations of

    public double circumference() {
        return 2 * PI * r;
    } // abstract methods. 
}

class Rectangle extends Shape {

    protected double w,  h;                               // Instance data

    public Rectangle(double w, double h) {               // Constructor
        this.w = w;
        this.h = h;
    }

    public double getWidth() {
        return w;
    }               // Accessor method

    public double getHeight() {
        return h;
    }              // Another accessor

    public double area() {
        return w * h;
    }                 // Implementations of

    public double circumference() {
        return 2 * (w + h);
    }  // abstract methods.
}

class Triangle extends Shape {
    protected double a,b,c,p;
  
  
    public Triangle(double a, double b, double c) {
        this.a = a;
        this.b = b;
        this.c = c;
          p = (a + b + c)/2;
    }


    public double area() {
       return Math.sqrt(p * (p - a) * (p - b) * (p - c));
    }


    public double circumference() {
        return a + b + c;
    }

}