Question

Code:

ClassA extends ClassBase {

 protected IntefaceA parA;
 .... }

 InterfaceA extends InterfaceBase

ClassBase {

 protected IntefaceBase parB;

 public method1() {

  parB.someMethod();
}

Code:

ClassA testClass=new ClassA();
testClass.setParA(new InterfaceA {....}; );
testClass.method1();

I receive null pointer exception because method metho1 uses class variable from ClassBase that used by method1 is parB. Does it possible have method1 use parA?
If not, I need copy&paste all code of method1 from base class to descendant.

Thanks.

Answer 1

Overriding fields is not possible in Java, only overriding methods. So what you can do is hide your parA / parB members behind a protected virtual getter, and access them only via the getter method. Then override the getter in ClassA to return parA instead of parB:

ClassBase {
  private IntefaceBase parB;

  protected IntefaceBase getPar() {
    return parB;
  }

  public method1() {
    getPar().someMethod();
  }
}

ClassA extends ClassBase {
  private IntefaceA parA;

  protected IntefaceBase getPar() {
    return parA;
  }
}