在类的构造函数中将对象作为参数传递有什么用？

Question

class Box {
private double width;
private double height;
private double depth;

// construct clone of an object
Box(Box ob) { // pass object to constructor
width = ob.width;
height = ob.height;
depth = ob.depth;
}

// constructor used when all dimensions specified
Box(double w, double h, double d) {
width = w;
height = h;
depth = d;
}

// constructor used when no dimensions specified
Box() {
width = -1; // use -1 to indicate
height = -1; // an uninitialized
depth = -1; // box
}

// constructor used when cube is created
Box(double len) {
width = height = depth = len;
}

// compute and return volume
double volume() {
return width * height * depth;
   }
}

// BoxWeight now fully implements all constructors.
class BoxWeight extends Box {
double weight; // weight of box
// construct clone of an object
BoxWeight(BoxWeight ob) { // pass object to constructor
super(ob);
weight = ob.weight;
}

// constructor when all parameters are specified
BoxWeight(double w, double h, double d, double m) {
super(w, h, d); // call superclass constructor
weight = m;
}

// default constructor
BoxWeight() {
super();
weight = -1;
 }

// constructor used when cube is created
BoxWeight(double len, double m) {
super(len);
weight = m;
   }
 }

class DemoSuper {
public static void main(String args[]) {
BoxWeight mybox1 = new BoxWeight(10, 20, 15, 34.3);
BoxWeight mybox2 = new BoxWeight(2, 3, 4, 0.076);
BoxWeight mybox3 = new BoxWeight(); // default
BoxWeight mycube = new BoxWeight(3, 2);
BoxWeight myclone = new BoxWeight(mybox1);

double vol;
vol = mybox1.volume();
System.out.println("Volume of mybox1 is " + vol);
System.out.println("Weight of mybox1 is " + mybox1.weight);
System.out.println();
vol = mybox2.volume();
System.out.println("Volume of mybox2 is " + vol);
System.out.println("Weight of mybox2 is " + mybox2.weight);
System.out.println();
vol = mybox3.volume();
System.out.println("Volume of mybox3 is " + vol);
System.out.println("Weight of mybox3 is " + mybox3.weight);
System.out.println();
vol = myclone.volume();
System.out.println("Volume of myclone is " + vol);
System.out.println("Weight of myclone is " + myclone.weight);
System.out.println();
vol = mycube.volume();
System.out.println("Volume of mycube is " + vol);
System.out.println("Weight of mycube is " + mycube.weight);
System.out.println();
   }
 }

在上面的代码中有人可以解释一下以下构造函数的用途是什么 方框（ Box ob ） 和 BoxWeight（ BoxWeight ob ）

我的意思是为什么我们要创建Box和BoxWeight对象＆＃39; ob＆＃39;并传递它 作为构造函数中的参数。

我只是想问一下复制构造函数的用途。我已经阅读了它的定义，但我没有理解。所以请用简单的语言帮助我理解这一点。 如果您有任何简单的例子让我理解，我们将不胜感激。