static variable initialization java

how to initialize a private static member of a class in java.

trying the following:

public class A {
   private static B b = null;
   public A() {
       if (b == null)
         b = new B();
   }

   void f1() {
         b.func();
   }
}

but on creating a second object of the class A and then calling f1(), i get a null pointer exception.