How can I create object of class whose constructor is defined as private

Question

I want to create object of Base class in another class but Base class constructor is defined as private

Here is my Code

public class Main
{
  public static void main(String ... args)
  {
    //Base objBase = new Base();
    //objBase.show();
  }
}


class Base
{
  private Base()
  {

  }

  public void show()
  {
     System.out.println("Base Class Show() Method");
  }
}

You could try reflection. But unless you are answering a interview question, then the best way would be to modify this code — Scary Wombat, Mar 25 '15 at 06:21
You can use reflection, but that defeats the purpose of having it private. — Bathsheba, Mar 25 '15 at 06:21
If that is your class, you can add a `static` factory method, to return the instance, or even make the constructor `non-private`. If it's not your class, then there is something wrong with the person who created it, if he hasn't given any way. May be you're not supposed to create it's instance? — Rohit Jain, Mar 25 '15 at 06:21
The reason it's private is likely because it needs to be constructed via some kind of builder of factory — MadProgrammer, Mar 25 '15 at 06:21
May be it is duplicate of http://stackoverflow.com/questions/23871173/how-to-create-objects-from-a-class-with-private-constructor?rq=1 and http://stackoverflow.com/questions/2599440/how-can-i-access-a-private-constructor-of-a-class?rq=1 — Unknown, Mar 25 '15 at 06:25
@MadProgrammer - Or because it is supposed to be a *Singleton* :P — TheLostMind, Mar 25 '15 at 06:31

score 4 · Accepted Answer · answered Mar 25 '15 at 06:21

Code inside Base is still allowed to call the constructor, which means it's possible to create objects in a static method:

class Base
{
  private Base()
  {

  }

  public void show()
  {
     System.out.println("Base Class Show() Method");
  }

  public static Base createBase() {
      return new Base();
  }
}

and then call the method to create an object:

Base objBase = Base.createBase();
objBase.show();

score 1 · Answer 2 · answered Mar 25 '15 at 06:24

1

You cannot create objects of classes if they have private constructors. Objects can be constructed, but only internally. That is how it is.

There are some common cases where a private constructor can be useful:

Singletons
Classes containing only static methods
Classes containing only constants
Type safe enumerations

Hoping this helps.

answered Mar 25 '15 at 06:24

spiralarchitect

880
7
19

Plus, there are people who think factory methods are more readable than constructors. If a class has more than one constructor, you can give factory methods different, descriptive names, and you can't do that with constructors. – ajb Mar 25 '15 at 06:36

How can I create object of class whose constructor is defined as private

2 Answers2