package cn.edu.bjut.chapter3;

public class Rectangle {
    double length, width; 
    
    // 构造函数
    public Rectangle(double length, double width) {
        this.length = length; 
        this.width = width;
    }
    
    // 构造函数
    public Rectangle(double length) {
        this(length, length)
    }
    ...
}