1. Unit 3 - Introduction to Inheritance - Example

2. Inheritance
In OOP a programmer can create a new class by extending an existing class
Superclass
(Base class)
subclass extends superclass
Subclass
(Derived class)

3. A Subclass... inherits fields and methods of its superclass
can add new fields and methods
can redefine (override) a method of the superclass
must provide its own constructors, but calls superclass’s constructors
does not have direct access to its superclass’s private fields

4. public class Pacer extends Walker{
public Pacer (int x, int y, Image leftPic, Image rightPic)
super (x, y, leftPic, rightPic); }
public void turnAround ()
Foot lf = getLeftFoot ();
Foot rf = getRightFoot ();
lf.turn (180);
rf.turn (180);
lf.moveSideways (-PIXELS_PER_INCH * 8);
rf.moveSideways (PIXELS_PER_INCH * 8);
Constructor
Calls Walker’s constructor using super
A new method
Calls Walker’s accessor methods

5. Example
Write a subclass of Walker called Bystander. Bystander should redefine (override) Walker’s firstStep, nextStep, and stop methods in such a way that Bystander alternates turning it’s left foot by 45 degrees left and right on subsequent steps but never moves the right foot. Bystander should also redefine the distanceTraveled method, to always return 0.
To redefine a superclass’ method in a subclass, keep its header but change the code inside the { }.
Define a new field which will help determine the direction of the left foot’s turn in each “step”.
Do not duplicate methods inherited that remain the same.