why copy constructor in java and what is use

[kundanranjan]

Hi,
any one please tell me why copy constructor in java and use.

Thanks
Regards
Kundan ranjan
software engineer
at HCL

[Ada Lovelace]

Java does(ish). They're just not called implicitly like they are in C++
and I suspect that's your real question.

Firstly, a copy constructor is nothing more than:

public class Blah {
  private int foo;
 
  public Blah() { } // public no-args constructor
  public Blah(Blah b) { foo = b.foo; }  // copy constructor
}

Now C++ will implicitly call the copy constructor with a statement like this:

Blah b2 = b1;

Cloning/copying in that instance simply makes no sense in Java because
all b1 and b2 are references and not value objects like they are in C++.
In C++ that statement makes a copy of the object's state. In Java it
simply copies the reference. The object's state is not copied so implicitly
calling the copy constructor makes no sense.

And that's all there is to it really.

Wishes Ada xx


[code]

[GregBrannon]

Google 'java copy constructor' for several good (and probably several not-so-good) articles on the use of copy/clone constructors in Java. I don't share Ada's position that they "make no sense" in Java.

In the future, Google first, then ask follow-up questions, referencing with links any of the search results you have questions about.