Exam 2 Topics
CS141: Introduction to Programming, Fall 2015

General Comments and Recommendations

• The exam will be focused on Chapters 6, 7, 9 and terminology in 5.10, 10.1, 10.2, 11 of the text. However, since the material is cumulative, you are still expected to be familiar with the earlier material.
• 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.
  • Review the reading quizzes.
  • Review the lab assignments.
• Practice Problems which could appear on the exam:
  • Practice Array problems (solutions are here.)
  • Old exams.
• Examples/Pictures
  • Pass by Value vs Pass by Reference (pdf)
  • Object Diagram Practice
  • Instance vs Static variables
    • Instance Variables
    • Class vs Instance Variables
    • Class vs Instance Methods

Chapter 6 A Second Look at Classes and Objects

• Object references
• Objects as method parameters and return types: Pass by Reference (not Pass by Value)
• The null keyword and Null Pointer Exceptions
• Self referencing using the keyword this
• Overloading: Methods with the same name but a different list of parameter types
• Class (static) methods and variables - class methods can only access class variables
  • Instance Variables
  • Class vs Instance Variables
  • Class vs Instance Methods
  • Only one copy exists of a static field regardless of how many objects that that type exist.
  • Don't need to create an object in order to access static fields, e.g. see Math class.
• Writing your own .equals method. Need to do this if you want to compare objects which contains instances of other objects (aggregation). Also consider the compareTo() method and the Comparable interface.
• Deep copying - don't create a copy using references of the member variables.
  Also, when returning a member variable, it can be safer to return a copy and not the reference.

Chapter 7 Arrays and the ArrayList Class

• What is an array? Why do we need them?
• Declaring 1-dimensional arrays. (Here are some old notes on 1D Arrays.)
• Accessing array elements
• Initializing arrays
  • one at a time.
  • Using for-loop
  • Using brackets
  • Using Arrays class.
  • Reading from a file. (we'll do this next week)
• Printing or Using arrays
  • one at a time.
  • Using for-loop
  • Using an enhanced loop
  • Using Arrays class.
• Array of primitives vs array of object/references
• Swapping elements in an array.
• Copying arrays.
• Comparing arrays.
• Partially filled arrays
• Accumulating values in an array.
• Arrays as return values and parameters in methods. Arrays are passed by reference. Recall Pass by Value vs Pass by Reference (pdf)
• Sorting
• Binary search
• ArrayLists: declaring, adding/removing elements, look at method list, copying, wrappers for primitive types
• Declaring multi-dimensional arrays. (Here are some old notes on 2D Arrays.)
  • Examples: Mazes, Game of Life, TicTacToe

Chapter 9 Inheritance

• 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.
• Don't overuse 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[i].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.
• Using the keyword final so that one can't override a method in the subclass.
• The universal super class: Object
  All Java classes are subclasses of the Object class and inherit the methods: toString(), equals(), hashCode(). These methods should generally be overriden.
• instanceof operator can be used to check what type of object you have. For example, if you need to cast an object. Should be used sparingly. Don't use as a way to implement different behavior, i.e. to bypass polymorphism.
• 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.
  • Examples: The Comparable interface
  • A class can have only one superclass but can implement multiple interfaces.

Chapter 5.10 Files, and Chapter 10.1-10.2 Exception Handling

Chapter 11 GUI Applications