Chapter 9 Exercises

1	Open your last version of the DoME project. Remove the print() method from class Item and move it into the Video and CD classes. Compile. What do you observe?	Compilation error.
2	In your DoME project, add a print() method in class Item again. For now write the method body with a single statement that prints out only the title. Then modify the print() methods in CDand Video so that the CD version prints out only the artist and the Video version prints only the director. This removes the other errors ecountered above. You should now have a situation coressponding to figure 9.4 in the text, with print() methods in three classes. Compile your project. This design should work, if there are errors remove them. Before executing, predict which of the print()methods will get called if you execute theDatabase list() method. Try it out: Enter a CD and a video into the database and call the Database list() method. Which print() methods were executed? Was your prediction correct? Try to explain your observations.	The CD and Video override The "super" method.
3	Modify your latest version of the DoME project to include the super call in the print() method. Test it. Does it behave as expected? Do you see any problems with this solution?	Yes it did. The order in which it prints may not be the one we want, I am not sure how you would go about to fix that.
4	Change the format of the output so that it prints the string "CD: " or Video: " (depending on the type of item) in front of the details.	Done.
5	Look up toString in the library documentation. What are its parameters? What is its return type?	No parameters. Return type String.
6	.... You can easily try this out. Create an object of class Video in your project, and then invoke the toString() method from theObject submenu in the object's popup menu.	Done.
7	The version of print() shown in Code 9.1 produces the output shown in text figure 9.9. Reorder the staements in the method in your version of the DoME project so that it prints the details as shown in text Figure 9.10.	CD Print. public void print()     {         System.out.print("CD: " + artist + ":   ");         super.print();         System.out.println("tracks: "+ numberOfTracks);     } Item "super" Print. System.out.print(title);         if (gotIt) {             System.out.println("*");         }         else {             System.out.println("");         }         System.out.println(playingTime + " minutes");         System.out.println(comment);
8	Having to use a superclass call in print() is somewhat restrictive in the ways we can format the output, because it is dependent on the way the superclass formats its fields. Make any necessary changes to the Item class and to the print() method of CD so that it produces the output shown in text Figure 9.11. Any changes you make to the Item class should be visible only to its subclasses. Hint: You used to use protected fields to do this.	You had to make the item fields protected.
9	Implement a transporter room with inheritancein your version of the zuul project.	???
10	Discuss how inheritance could be used in thezuul project to implement a player and a monster class.	???
11	Could (or should) inheritance be used to create an inheritance relationship (super-, sub-, or sibling class) between a character in the game and an item?	???
12	Assume you see the following lines of code: Device dev = new Printer(); dev.getName(); Printer is a subclass of Device. Which of these classes must have a definition of methodgetName() for this code to compile?	Device is the super class, but couldnt printer have a method that overrides it? ##ask Daly##
13	In the same situation as in the previous exercise, if both classes have an implementation of method getName(), which one will be executed?	The printer's method overrides and gets executed.
14	Assume you write a class Student, which does not have a declared superclass. You do notwrite a toString() method. Consider the following lines of code. Student st = new Student(); String s = st.toString(); Will these lines compile? What exactly will happen when you try to execute?	Should work fine, student is a subclass of object.
15	In the same situation as the previous exercise (class Student, no toString() method), will the following lines compile? Why? Student st = new Student(); System.out.println(st);	yes, toString() is called automatically.
16	Assume your class Student overrides toString()so that it returns the student's name. You now have a list of students. Will the following code compile? If not, why not? If yes, what will it print? Explain in detail what happens. Iterator it = myList.iterator(); while (it.hasNext()) {         System.out.println(it.next()); }
17	Write a few lines of code that result in a situation where a variable x has the static type T and the dynamic type D.

Chapter 8 Test

this got deleted for some reason. Maybe it didnt post correctly. Ill try to get it up as soon as possible.

Chapter 8 Exercises

1	Open the project dome-v1. It contains the classes exactly as they were discussed in the text. Create some CD objects and some video objects. Create a database object. Enter the CDs and videos into the database, and then list the database contents.	Done.
2	Try the following. Create a CD object. Enter it into the database. List the database. You see that the CD has no associated comment. Add a comment to the CD object on the object bench (the one you entered into the database). When you now list the database again, will the CD listed there have a comment attached? Try it. Explain the behavior you observe.	CD: I love APCS    (84 minutes)     FDaly     tracks: 32     Computers are the future
3	Draw an inheritance hierarchy for the people in your place of study.	Jackover --> appartmet heads --> teachers --> students
4	Open the project dome-v2. This project contains a version of the DoME application rewritten to use inheritance, as described in the text. *Note that the class diagram displays the inheritance relationship. Open the source code of the Video class and remove the "extends Item" phrase. Close the editor. What changes do you observe in the class diagram? Add the "extends Item" phrase again.	The arrow connecting DVD to item was gone
5	Create a CD object. Call some of its methods. Can you call the inherited methods(for example setComment())? What do you observe about the inherited methods?	The inherit properly.
6	Set a breakpoint in the first line of the CDclass's constructor. Then create a CD object. When the debugger window pops up, use Step Into to step through the code. Observe the instance fields and their initialization. Describe your observations.	It went to the item class then back to the CD class. It inherited.
7	Open the dome-v2 project. Add a class for video games to the project. Create some video game objects and test that all the methods work as expected.	public class VideoGame extends Item {     private String gameName;     private int numberOfPlayers;          public VideoGame(String theTitle, int time)     {         super(theTitle, time);         gameName = theTitle;         numberOfPlayers = time;     }     /**      * @return The artist for this CD.      */     public String getgameName()     {         return gameName;     }     /**      * @return The number of tracks on this CD.      */     public int getNumberOfPlayers()     {         return numberOfPlayers;     } }
8	Order these items into an inheritance hierarchy: apple, ice cream, bread, fruit, food-item, cereal, orange, dessert, chocolate mousse, baguette.	(apple, orange)--> fruit (cereal, baguette)--> bread (Chocolate mousse, ice cream)--> dessert (Fruit, bread, dessert)--> food
9	In what inheritance relationship might a touch pad and a mouse be?	(touch pad --> mouse)
10		The square is a subclassof rectangle because of the fact that every square is a rectangle but not the vise versa.
11	Assume we have four classes: Person, Student, Teacher & PhDStudent. Teacher and Student are both subclasses of Person. PhDStudent is a subclass of Student. Which of the following assignments are legal and why? Person p1 = new Student(); Person p2 = new PhDStudent(); PhDStudent phd1 = new Student(); Teacher t1 = new Person(); Student s1 = new PhDStudent(); s1 = p1; s1 = p2; p1 = s1; t1 = s1; s1= phd1; phd1 = s1;	In the third declaration p1 = s1 student is a person In the fifth declaration s1 = phd1 PhDStudent is a student
12	Test your answers to the previous question by creating the classes mentioned in that exercise, and trying it out in BlueJ.	It worked.
13	What has to change in the Database class when another item subclass (for example classVideoGame) is added? Why?	Nothing? it shouldn't affect anything.
14	Use the documentation of the standard class libraries to find out about the inheritance hierarchyof the collection classes. Draw a diagram showing the hierarchy. http://java.sun.com/j2se/1.4.2/docs/api/	collection --> Abstract collection--> AbstractList, AbstractSet AbstractList --> ArrayList, Vector, AbstractSequentialList AbstractSet --> HashSet, TreeSet Hashset --> JobStateReasons, LinkedHashSet
15	Go back to the lab-classess project from chapter 1. Add instructors to the project. Use inheritance to avoid code duplication between students and instructors.	Partially complete, had a few mistakes,
16	Draw an inheritance hierarchy representing parts of a computer system (processor, memory, disk drive, CD drive, printer, scanner, keyboard, mouse, etc.)	All are subclasses of processor I believe. They work independently being controlled by the processor.
17	Look at the code below. You have four classes (O,X,T and M) and a variable of each of these. O o; X x; T t; M m; The following assignments are all legal. m = t; m = x; o = t; The following assignments are all illegal. o = m; o = x; x = o; What can you say about the relationships of these classes?	M is the the highest in the hierarchy, then its subclasses are O and X and finally underneath that is T.
18	Draw an inheritance hierarchy of AbstractListand all its (direct and indirect) subclasses, as they are defined in the Java standard library. http://java.sun.com/j2se/1.4.2/docs/api/	AbstractList --> AbstractSequentialList, Vector, Arraylist AbstractSEquentialList --> LinkedList Vector --> Stack