Question

I am trying to understand what is the difference between the following constructors in java in class

Box
{
    Box(Box ob)
    {
     width = ob.width;
     height = ob.height;
     depth = ob.depth;
    }

    Box(double w, double h, double d)
    {
     width = w;
     height = h;
     depth = d;
    }

    Box()
    {
     width = 0;
     height = 0;
     depth = 0;

    }

    Box(double width, double height, double depth)
    {
     this.width = width;
     this.height = height;
     this.depth = depth;
    }
}

Cheers everyone

Answer 1

First is the copy constructor which is used to copy the values of one object to another during initialization.

Second and Fourth is a parametrized constructor which contains all the data members of the class. But it is recomended to use the fourth and most of the IDE(all that I know) will auto generate the 4th as it is easier to read and has the same context

Third is a default constructor. Used to set default values. See it does not take any inputs(as parameter)

Box b = new Box();//Default constructor
Box b1 = new Box(1.0,2.0,3.0);//Parameterized constructor completely defining the object
Box b2 = new Box(b1);//Copy constructor will copy the values but both will have a different reference
b2 = b1;//b2 now refers to object referenced by b1. So the earlier reference for b2 will be taken by GC(garbage Collector)