2、创建一个名为Rectangle的类来表示一个矩形,矩形的长度和宽度由构造方法来确定（要求长和宽的范围为0~50）.为

public class Rectangle {
double chang,kuan;
public double getArea(double chang,double kuan){
return chang*kuan;
}
public double getPerimeter(double chang,double kuan){
return (chang+kuan)*2;
}
public Rectangle(){
}

public Rectangle(double chang,double kuan){
if(0