How can I create an object of this class?

Question

In class B, how can I create an object of class A other than the process of object creation (i.e. without creating an object having null)?

class A
  {
    public int one;  
   A(A a)
    {
      a.one=1;
    }
  }
class B
  {
   public static void main(String...args)
     {
     //now how to create an object of class A over here.
     }
  }

Answer 1

To construct an object of type A you need to pass to the constructor either a reference to another object of type A, or else the null reference. So you have only two options:

A a1 = new A(null);
A a2 = new A(a1);

The first time you create an object of type A you must use the null reference because you don't have any other objects of type A.

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Update

After you changed your question, I don't think it's possible to construct an object of type A.

Answer 2

If I understand your question correctly, you want to create an object a without having to pass it a pre-existing object of the same type.

To do so you have to add a constructor to class A that does not take a parameter of type A or modify the existing one:

class A
    {
        A() {
            // Constructor logic.
        }
        A(A a) {
            // Constructor logic when passing an existing object of the same type, perhaps to create a clone.
        }
    }

If for some reason you can't modify class A, you'll have to follow Mark Byers' answer and pass a null reference to the constructor.

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Update

With the update to your code, this problem (or thought experiment) is unsolvable: class A can not be instantiated as written.