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Learn Java with Projects
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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.
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 {}.
While we...