Prevent a class from being extended

  • When you define a class, you can control whether your class can be used as a super class

  • Suppose you do not want your class to be used as a super class

    • How can you stop Java from using your class as super class ?

  • A class with the final qualifier cannot be extended (i.e., used as a superclass)

    Example: 

    /* ======================================
   This class cannot be extended
   ====================================== */
public final class myClass 
{

   // Data fields, constructors, and methods omitted

}

DEMO: demo/04-inheritance/23-final-class/Circle.java + GeometricObject.java

Prevent a (inherited) method from being overridden

  • Suppose you define a class that will be used as a super class, but you do not allow some method(s) in the class to be overriden

    • How can you stop some program from overriding your methods after inheriting from your class ?

  • A method with the final qualifier cannot be overridden in a subclass: 

    public class myClass  // Class can be used as super class
{
    ....

    /* =============================================
       But: this method cannot be overridden
       ============================================= */
    public final void method1()
    {
        // Do something
    }

    ....
}

DEMO: demo/04-inheritance/23-final-method