Lecture 28: Abstract Classes & Inheritance Announcements & Review Lab 8 Due Thursday Image and color effects with 2D arrays Read: –Chapter 9 Cahoon & Davidson –Chapter 9 Regis & Stepp Additional Reading: va/concepts/inheritance.html Last Time Review Inheritance Dynamic dispatch Today Dynamic dispatch Abstract Classes

Lecture 28: Abstract Classes & Inheritance Inheritance in Java... Object TransformationGraphRectangle ColoredRectangle Object provides these methods: toString() equals() // more on these clone() // later... instanceof() All classes inherit from Object Rectangle inherits from Object ColoredRectangle inherits from Rectangle

Lecture 28: Abstract Classes & Inheritance Super class: Rectangle public class Rectangle { protected int width; // the instance variables protected int height; public Rectangle() { width = 0; height = 0; } public Rectangle(int w, int h) { width = w; height = h; } public void draw(...) {}

Lecture 28: Abstract Classes & Inheritance Syntax of Inheritance Example: ColoredRectangle public class ColoredRectangle extends Rectangle { private Color myColor; // additional instance variables public ColoredRectangle() { super(); // optional myColor = Color.white; } /* Is the same as: public ColoredRectangle() { implicitly first calls super, because the signatures match myColor = Color.white; } */ public ColoredRectangle(int w, int h, Color newColor) { super(w,h); // required: why do we need this one? myColor = newColor; }

Lecture 28: Abstract Classes & Inheritance Dynamic Dispatch Declare variables of supertype and they can be the supertype or the subtype Rectangle r = new ColoredRectangle(); Declare variables of a subtype and they can only be of type subtype or lower. Test type with instanceof returns a boolean if (r instanceof Rectangle) {...} if (r instanceof ColoredRectangle) {...} BlueJ

Lecture 28: Abstract Classes & Inheritance Abstract Classes Want to partially declare a class Force an implementation of a method but do not offer a default implementation it –require a draw method, but have not default draw

Lecture 28: Abstract Classes & Inheritance Syntax for Abstract Classes public abstract class Shapes { protected static String name; // e.g., Rectangle, Triangle,... // Subclass must implement draw public abstract void draw(DrawingBox box); public String getName() { // Subclass need not implement getName return name; } public class Rectangle extends Shapes { protected static String name = “Rectangle”;.... public void draw(DrawingBox box) { box.drawRect(...) }

Lecture 28: Abstract Classes & Inheritance BlueJ examples...

Lecture 28: Abstract Classes & Inheritance Interfaces Want to partially specify a behavior that can apply to lots of classes –For example, adding Color Enforces a consistant application of a “feature” across lots of classes

Lecture 28: Abstract Classes & Inheritance Interfaces Interface Colorable { public void setColor(Color c); public Color getColor(); } public class ColorRectangle extends Shapes implements Colorable{ Color myColor; public void setColor(Color c) { myColor = c; } public Color getColor() { return myColor; }