Java Field Hiding

Question

I was wondering what it means to say a field is hidden between 2 java classes and what it means when running code in terms of resulting output?

I have an abstract class with a protected static boolean field = false and a sub class which has a boolean field with the same name but is not static and set to true.

If I had this code:

Superclass d = new subclass();

what would be the value of the boolean field in the superclass and the boolean field in the subclass? Does subclass field stay as false after the assignment above?

Answer 1

• Java Language Specification

  If the class declares a field with a certain name, then the declaration of that field is said to hide any and all accessible declarations of fields with the same name in superclasses, and superinterfaces of the class.

  A hidden field can be accessed by using a qualified name if it is static, or by using a field access expression that contains the keyword super or a cast to a superclass type.

  ^{See more in http://docs.oracle.com/javase/specs/jls/se7/html/jls-8.html}

• Example Code

  class A {
      static int field;
  }
  class B extends A {
      int field;
      void doSomething() {
          System.out.println(super.field); // From A
          System.out.println(field); // From B
      }
  }
  class Main {
      public static void main(String[] args) {
          B b = new B();
          System.out.println(b.field); // From B
          System.out.println(((A) b).field); // From A
          System.out.println(A.field); // From A
      }
  }