Java Strange Behaviour

    public class HelloWorld
    {
      public static void main(String[] args)
      {
        Test test = new Test();
        test.setA( test.a );

        if( test.a==null){
          System.out.println("a is null ");
        } else {
          System.out.println("a is not null ");
        }

      }
    }

    public class A{
    }

    public class Test{
      A a; //use this and a is null
      //A a = new A(); //use this and a is not null

      void setA(A a){
        a = new A();
      }

    }