Java flow-control -

can explain why code giving output null? when try call new a() instead of new b(), printing current date.

class {     date d = new date();      public a()     {         printdate();     }      void printdate()      {         system.out.println("parent");         system.out.println(d);     } }  class b extends {     date d = new date();      public b()     {         super();     }      @override     void printdate()     {         system.out.println("child");         system.out.println(d);     } }  public class test  {     public static void main(string[] args)      {         new b();     } } 

new b() invokes constructor of b, invokes constructor of a. a's constructor calls printdate(), which, due overriding, executes b's printdate(), prints value of d variable of b. however, d variable of b not initialized yet (it initialized after constructor of executed). therefore still null (which default value reference variables).

on other hand, when create instance of a (new a()), printdate of a called, , prints d variable of a, initialized prior constructor of a being executed.

in case it's not clear, b.d not override a.d, hides it. methods can overridden.