Implementation Inheritance

Notes from Josh Hug's lecture videos.

Extends

extends is used when a class has an is-a relationship with another class.

public class Steven extends BaldMan {
    //Stuff...
}

In this example, Steven inherits from BaldMan the following.

• All instance and static variables.

• All methods.

• All nested classes.

• UNLESS they are private.

• ... and UNLESS the method is a constructor.

super

In order to access members in the superclass, you must call the super keyword. This is useful for avoiding repetition, especially if you're overriding methods that use private fields and want to keep the original implementation.

public class Steven extends BaldMan {
    @Override
    public void applyRogaine() {
        super.applyRogaine(); // Do everything the original method did...
        System.out.println("Steego"); // But also print this.
    }
}

The constructors of subclasses can call the constructor of the superclass using super(params);If you don't Java will do it implicitly.

Encapsulation

Implementation inheritance breaks encapsulation in such a way that working changes to the superclass can cause issues in the subclass without any changes in the subclass.