Exam 3 Topics
CS141: Introduction to Programming, Fall 2013

General Comments and Recommendations

• The exam will cover Chapters 1-10 of the text.
• The exam will be 1 hour long. It will be closed book. Electronic devices, of any kind, will not be allowed.
• It is strongly recommended that students:
  • Re-read the text
  • Do the self-check exercises in each chapter (answers are in the text)
  • Review the reading quizzes
  • Review the programming code-completion and programming exercises.

Chapters 1-4:

• See Exam 1 review material

Chapters 5-8:

• See Exam 2 review material

Chapter 9: Inheritance and Interfaces

Vocabulary

Inheritance superclass subclass extends override implements

Abstract (vs concrete) class super Polymorphism protected access inheritance hierarchy interface the Object class

Topics

• What is inheritance and why use it?
• Subclasses vs superclasses - See Hierarchy
• A class can have only one direct superclass. A class can have multiple subclasses.
• Subclasses:
  • How are they defined (using extends)
  • Overriding methods
  • What variables and methods in the super class can be accessed by the subclass?
    • Public vs Protected: Protected modifier allows access by all subclasses and all classes in the same package (folder). Your text suggests leaving variables as private.
    • Private variables in the superclass are not accessible from the subclass.
    • Using super() in the first line of constructor
    • Using super.method_name() anywhere in a subclass method.
• Polymorphism:

      Shape[] shapes = new Shape[3];
      shapes[0] = new Circle(2);
      shapes[1] = new Rectangle(2,3);
      shapes[2] = new Square(5);
      for (int i=0; i < shapes.length; i++) {
  	     System.out.println("The area for " + shapes[i] + " is " + shapes.calcArea());
       }
  

  • Which toString() method is called? Which calcArea() is called? The one in superclass (Shape) or in the subclass (Circle, Rectangle, Square)?
• Abstract class:
  • Declare as

    public abstract class Shape { 
    	    public abstract double calcArea(); 
    	    ... 
    

    Must define method in the subclass. Can't create a Shape object; can only create a subclass.
• The universal super class: Object
  All Java classes are subclasses of the Object class and inherit the methods e.g. toString(), equals(). These methods should generally be overriden.
• Interface - using the implements keyword.
  • An interface has no variables, only methods which are not implemented.
  • An interface is used to force a class to define a set of methods so as to force consistency across a set a classes.
  • A class can have only one superclass but can implement multiple interfaces.
• In a Nutshell: What is the difference between a class, an abstract class, and an interface?
  • Class: Can contain data and methods. All methods must be implemented.
  • Abstract Class: Can contain data and methods. Not all methods are implemented. The methods that aren't, are called abstract and at some point must be implemented in a concrete subclass.
  • Interface: Contains no data (except perhaps constants). None of the methods are implemented.
• And where:
  • A class "implements" an interface. A subclass "extends" a superclass.
  • A class can have only one superclass but can implement multiple interfaces.
  • An object cannot be created from an abstract class or interface. An object can only be created from a concrete class.

Chapter 10: Graphical User Interfaces

You are required to know the vocabulary but you will not be asked to write code related to this topic.

Vocabulary

Events Event Loop Event Queue Listening to Events Event listeners Event source Event Handling

GUI Components Local Inner classes Anonymous Inner classes Components: Text Fields, Text Areas RGB Color Swing and AWT Libraries