求用Java编一个小程序

class Retangle{

static public double countArea(double d1,double d2){
return d1*d2;
}
static public double countgirth(double d1,double d2){
return 2*(d1+d2);
}
使用static方法，不需要创建实例

class Retangle{
private double length;
private double width;
//构造函数
Retangle(double length,double width){
this.length = length;
this.width = width;
}
//方法
public double getArea(){
return length*width;
}
public double getGirth(){
return 2*(length+width);
}
public static void main(String[] args){
Rectangle rec = new Rectangle(3,4);
System.out.println("面积为："+rec.getArea());
System.out.println("周长为："+rec.getArea());
}
}

public void luqiang(){
public void Retangle(double length, double width){
double mianji,zhouchang;
mianji=length*width;
System.out.println("面积："+mianji);
zhouchang=(length+width)*2;