Lab 8: Image and Color Effects with 2D Arrays

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

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

3. 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

4. Syntax of InheritanceExample: 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

5. 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 <variable instanceof TypeName> returns a boolean if (r instanceof Rectangle) {...} if (r instanceof ColoredRectangle) {...} • BlueJ Lecture 28: Abstract Classes & Inheritance

6. 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

7. 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

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

9. 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

10. 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; } Lecture 28: Abstract Classes & Inheritance