package com;

public class Rectangle1 {
    private double width;
    private double length;

    public Rectangle(){
        this.width=5;
        this.length=6;
    }
   
    public Rectangle(double w,double l){
        this.width=w;
        this.length=l;
    }

    public double area(){        //求面积        
        return this.width*this.length;
    }
     
    public double perimeter(){    //求周长
        return 2*(this.width+this.length);
    }
   
    public static void main(String[] args) {
        Rectangle r1=new Rectangle();
        System.out.println("r1的周长："+r1.perimeter());
        System.out.println("r1的面积："+r1.area());
        
        System.out.println();
        Rectangle r2=new Rectangle(10,20);
        System.out.println("r2的周长："+r2.perimeter());
        System.out.println("r2的面积："+r2.area());
    }
        public double getWidth() {
        return width;
    }

    public void setWidth(double width) {
        this.width = width;
    }

    public double getLength() {
        return length;
    }

    public void setLength(double length) {
        this.length = length;
    }


}红色的这几行为什么要有？搞不懂

public class Rectangle{
    private int length,width;
    public Rectangle(){
        this(5,10);
        System.out.println("Premeter is"+((length+width)*2));
    }
    public Rectangle(int a,int b){
        
        int area;
        area=a*b;
        System.out.println("area is"+area);
    }
    public static void main(String args[]){
        
        Rectangle Rec=new Rectangle();
   
        
    }
}
        
        
        上面那个是老师给的，这个是我自己编的。没有用到get set一样可以调用私有变量呀

原来是这样子，懂了！感谢