What is the use for a constructor take the same type as a parameter? Java

Question

Something like this:

Class Object{

    Object(Object obj){}

}

When do you need to do that? I just like to know an example or two.

Answer 1

Mainly used for copy constructor. An example can be as follows:

Like C++, Java also supports copy constructor. But, unlike C++, Java doesn’t create a default copy constructor if you don’t write your own.

class Complex {

    private double re, im;

    // A normal parametrized constructor
    public Complex(double re, double im) {
        this.re = re;
        this.im = im;
    }

    // copy constructor
    Complex(Complex c) {
        System.out.println("Copy constructor called");
        re = c.re;
        im = c.im;
    }
    ...

You can refer here for more info.

Answer 2

This can be an effective way of duplicating an existing object or modifying one slightly.

I once worked on a Checkers board game project where Board and Move were represented as classes. In order to create a new game board the class Board had a constructor that accepted another Board instance as well as a Move instance. The constructor made a new game board that would exist if the Move had been applied to the original board.

That is just one example.