实训一：构建圆和矩形对象

//Circle.java    
class Circle{                                            //圆类
    private double radius;                              //半径字段
    private double x, y;                                //圆心坐标字段
    private static int num;                             //圆对象个数字段
    public static final double PI = 3.14159;            //圆周率常量字段
    public Circle(){                                    //构造方法1
        num ++; 
    }
    public Circle(double radius) throws Exception{      //构造方法2
        if (radius < 0) { throw new Exception("负数不能做圆半径"); }
        else {
            this.radius = radius;
            num ++;
        }
    }
    public double getRadius(){                          //获取半径方法
        return radius; 
    }
    public void  setRadius(double radius) throws Exception{  //设置半径方法
        if (radius < 0) { throw new Exception("负数不能做圆半径"); }
        else { this.radius = radius; }
    }
    public static int getNum(){                         //获取圆对象个数方法
        return num;
    }
    public double calcArea(){                           //计算面积方法
        return PI * radius * radius;
    }
    public double calcGirth(){                          //计算周长方法
        return 2 * PI * radius;
    }
}
//Train1.java
import java.util.Scanner;
public class Train1 {
    public static void main(String[] args){
        System.out.println(" ==== 构建圆对象并计算其面积周长 ====");
        try{
            Circle aCircle;
            double radius;
            String str;
            Scanner scan = new Scanner(System.in);
            while(true){    
                System.out.println("请输入半径（直接按回车键结束程序）：");
                str = scan.nextLine();
                if (str.equals("")) { break; }
                radius = Double.parseDouble(str);
                aCircle = new Circle(radius);
                System.out.printf("构建了半径为%.2f的圆，圆面积%.2f、周长%.2f\n",
                        aCircle.getRadius(), aCircle.calcArea(), aCircle.calcGirth());
                System.out.printf("目前圆个数为 %d\n",Circle.getNum());
            }
            scan.close();
        }
        catch(Exception e){ System.out.println("异常：" + e); }
        finally { System.out.print("——程序结束。"); }
    }
}

import java.util.Scanner;
class Rectangle{        //矩形类
    private double length;
    private double width;
    private static int num;    //矩形对象个数
    public Rectangle(){
        num ++; 
    }
    public Rectangle(double length, double width){
        this.length = length;
        this.width = width;
        num ++; 
    }
    public double calcArea(){   //计算面积
        return length * width;
    }
    public double calcGirth(){  //计算周长
        return (length + width) * 2;
    }
    public double getLength(){ return length; }
    public void  setLength(double length){
        this.length = length;
    }
    public double getWidth(){ return width; }
    public void  setWidth(double width){
        this.width = width;
    }
    public int getNum(){ return num; }
}
public class Train2 {
    public static void main(String[] args){
        System.out.println(" ==== 构建矩形对象并计算其面积周长 ====");
        try{
            Rectangle aRectangle;
            double length, width;
            String str;
            Scanner scan = new Scanner(System.in);
            while(true){    
                System.out.println("请输入长度（直接按回车键结束程序）：");
                str = scan.nextLine();
                if (str.equals("")) { break; }
                length = Double.parseDouble(str);
                System.out.println("请输入宽度：");
                str = scan.nextLine();
                width = Double.parseDouble(str);
                aRectangle = new Rectangle(length, width);
                System.out.printf("构建了长%.2f、宽%.2f的矩形，其面积%.2f、周长%.2f\n",
                        aRectangle.getLength(), aRectangle.getWidth(), aRectangle.calcArea(), aRectangle.calcGirth());
                System.out.printf("目前矩形个数为 %d\n",aRectangle.getNum());
            }
            scan.close();
        }
        catch(Exception e){ System.out.println("异常：" + e); }
        finally { System.out.print("——程序结束。"); }
    }
}