用Java编写一个类为Rectangle 该类有两个属性 长length和宽width默认值为1该两个变量为私有的即private其它方法为：构造方法：public Rectangle； Public Rentangledouble length double width; 方法：矩形对象调用该方法可以得到面积：public double getArea矩形对象调用该方法可以得到周长：pu

Rectangle类的代码如下：

public class Rectangle {
    private double length;
    private double width;
    
    public Rectangle() {
        this.length = 1;
        this.width = 1;
    }
    
    public Rectangle(double length, double width) {
        this.length = length;
        this.width = width;
    }
    
    public double getArea() {
        return length * width;
    }
    
    public double getPerimeter() {
        return 2 * (length + width);
    }
    
    public void setWidth(double width) {
        this.width = width;
    }
    
    public void setLength(double length) {
        this.length = length;
    }
    
    public double getWidth() {
        return width;
    }
    
    public double getLength() {
        return length;
    }
}

测试类的代码如下：

public class RectangleTest {
    public static void main(String[] args) {
        Rectangle r1 = new Rectangle();
        System.out.println("r1: length=" + r1.getLength() + ", width=" + r1.getWidth());
        System.out.println("r1: area=" + r1.getArea() + ", perimeter=" + r1.getPerimeter());
        
        Rectangle r2 = new Rectangle(3, 4);
        System.out.println("r2: length=" + r2.getLength() + ", width=" + r2.getWidth());
        System.out.println("r2: area=" + r2.getArea() + ", perimeter=" + r2.getPerimeter());
        
        r1.setWidth(2);
        r1.setLength(3);
        System.out.println("r1: length=" + r1.getLength() + ", width=" + r1.getWidth());
        System.out.println("r1: area=" + r1.getArea() + ", perimeter=" + r1.getPerimeter());
    }
}

输出结果如下：

r1: length=1.0, width=1.0
r1: area=1.0, perimeter=4.0
r2: length=3.0, width=4.0
r2: area=12.0, perimeter=14.0
r1: length=3.0, width=2.0
r1: area=6.0, perimeter=10.0

可以看到，Rectangle类中的方法都能正常工作，测试类也能够正确地测试这些方法