square draw() rotate() setlength() getlength() circle draw() getradius() setradius() shape erase()...
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Lecture 16COP3502: Introduction to CIS I
TodayInterfaces and Polymorphism
Wednesday, Friday, MondayGUIs, Animation, Events
In-class reviewWed Feb 26
In-class Exam Fri Feb 28
Will cover everything up through next Monday’s class
Super SessionThursday Feb 27 8pm-10pm
Tuesday Feb 18Lab 3 (Objects)
Tuesday Feb 25Lab 4 (GUIs)
Problem Set 3
Reading
Thinking in Java (Eckel)Ch. 1
Intro to Java Programming (Eck)Ch. 5
Square
draw()rotate()setLength()getLength()
Circle
draw()getRadius()setRadius()
Shape
Erase()Move()setX()setY()setColor()getPos()getColor()
Triangle
draw()rotate()setLength()getLength()
Hexagon
draw()rotate()setLength()getLength()
classes can be both a superclass and a subclass at the same time!
Reptile
move()eat()reproduce()
Animal
move()eat()reproduce()
Mammal
move()eat()reproduce()
Fish
move()eat()reproduce()
Lion Tiger Bear
classes can only inherit from one superclass
uses of inheritance
1. Organizing information2. Grouping similar classes
3. Modeling similarity among classes4. Creating a taxonomy among objects
What does the subclass inherit?
public methodsprotected methods
protected instance variables
What does the subclass inherit?
public methodsprotected methods
protected instance variables
NOT PRIVATE ANYTHING
subclass specializes superclass
subclass specializes superclass
adding new methods
subclass specializes superclass
adding new methodsoverriding existing methods
subclass specializes superclass
adding new methodsoverriding existing methods
Implementing abstract methods
subclass specializes superclass
adding new methodsoverriding existing methods
Implementing abstract methods
Superclass “factors out” common capabilities among subclasses
abstract methods
empty methods in the superclassneed to be implemented by inheriting subclass
uses abstract keyword
abstract methods
empty methods in the superclassneed to be implemented by inheriting subclass
uses abstract keyword
abstract void draw();
any class with an abstract method should itself be declared abstract
abstract class Shape {…abstract void draw();…
}
overriding methods
public class Square extends Shape {…@Overridepublic void draw() {
…}…
}
method resolution
compiler walks up the class inheritance hierarchy tree until it finds the appropriate method
super keyword
public class Square extends Shape {…public Square(double x, double y, Color c, double len) {
super(x, y, c);length = len;
}…
}
super keyword
public class Shape {…public void rotate(double radians) {
//perform rotation}…
}
Pretend this method exists in our Shape implementation!
super keyword
public class Square extends Shape {…@Overridepublic void rotate(double degrees) {
double radians = Math.PI*degrees/180;super.rotate(radians);
}…
}
Same as Shape.rotate()
super keyword
public class Square extends Shape {…@Overridepublic void rotate(double degrees) {
double radians = Math.PI*degrees/180;super.rotate(radians);
}…
}
Same as Shape.rotate()
partial overriding
classes can only inherit from one superclass
classes can only inherit from one superclass
But they can inherit from multiple interfaces
Subclass
Superclass Interface Interface
interface
a set of instance methods without any implementation
ie. a collection of abstract methods
interface
“factors out” commonality among very different classes that share behavior
both have the ability to be “colored”might implement a Colorable interface
interfaces declare methods, but don’t include any implementation
interfaces
No constructorusually no instance variablesjust a list of responsibilities
even more abstract than abstract classes
uses of interfaces
give specific properties to an objectUsually an adjective that ends in –ive or –able
ColorableRotatable
Bounceable
uses of interfaces
give role to an objectUsually ends in –er
ContainerMover
Teacher
public interface Colorable {
// set the current colorpublic void setColor(Color color);
// get the current colorpublic Color getColor();
}
public interface Decorable {
// models something which can be decorated public void decorate(Decoration dcr); }
interfaces can extend any number of other interfaces
subclass inherits all superclass methods AND all interfaces
public interface Artistic extends Colorable, Decorable {
// probably uses decorate and change color methods public void putOnDisplay(); }
Class Interface
Models an object with properties and behavior
Models a role and defines a set of responsibilities
Factors out common properties and behavior of similar objects
Factors out common behavior, but not properties, of usually dissimilar objects
Declares methods and may define some or all of them
Declares but does not define methods
Can only extend one superclass Can extend multiple interfaces
Can implement any number of interfaces
No implementation
methods for factoring out common code
loops and functions
methods for factoring out common code
loops and functionsclasses and instances
methods for factoring out common code
loops and functionsclasses and instances
superclasses and subclasses
methods for factoring out common code
loops and functionsclasses and instances
superclasses and subclassesinterfaces and implementations