Applying inheritance

As we learned in the previous section, inheritance creates an “is-a” relationship hierarchy. This enables base class functionality to be inherited and therefore available to subclasses, without any extra coding. Java uses two keywords in applying inheritance: extends and implements. Let’s discuss them now.

extends

This is the principle keyword that’s used and relates to both classes and interfaces. Regarding classes, we state that class Sub extends Base {}. In this case, all of the non-private members from the Base class will be inherited into the Sub class. Note that private members and constructors are not inherited – this makes sense as both private members and constructors are class-specific. In addition, Java prohibits multiple class inheritance. This means that you cannot extend from more than one class at a time. Regarding interfaces, we state that interface ChildInt extends ParentInt {}.

implements

While we...