Chapter 9 Exercises

Barnes and Kolling Chapter Nine Questions

Barnes and Kolling Chapter Nine Questions

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?	the item  class compiles. however the DVD class and CD class cannot access the superclass fields.
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 CD andVideo 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.	public void print()     {         System.out.print("title: " + title);              }   public void print()     {         System.out.print("Director:" + director);             } public void print()     {         System.out.print("Artist:" + artist);             } The class compiles!
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?	public void print()     {         super.print();         System.out.print("Artist:" + artist); it compiles and behaves same as before
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.	public void print()     {         super.print(); System.out.println("CD:")         System.out.print("Artist:" + artist);
5	Look up toString in the library documentation. What are its parameters? What is its return type?	no parameters it returns 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.	OK
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.	print method in CD: public void print()     {         System.out.print("CD: " + artist + ":   ");         super.print();         System.out.println("tracks: "+ numberOfTracks);     } print method in Item: 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.	?????
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, since it is the superclass
13	In the same situation as in the previous exercise, if both classes have an implementation of methodgetName(), which one will be executed?	The method in class printer
14	Assume you write a class Student, which does not have a declared superclass. You do not write 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?	Student is a subclass of OBJECT, therefore the method will work since it is invoked from the object class.
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, it will return the toString output since it is in the Superduper class object.
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 thedynamic type D.	T x = new D;

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Barnes and Kolling Chapter Eight Questions

Barnes and Kolling Chapter Eight Questions

Barnes and Kolling Chapter Eight Questions

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: Death Magnetic (70 mins)     Metallica     tracks: 12     <no comment> CD: Death Magnetic (70 mins)     Metallica     tracks: 12     Great album it seems to add the comment string to the database class, we may infer that database class responds to other class changes
3	Draw an inheritance hierarchy for the people in your place of study.	Jonathan --> Daly--> Jackover--> WBAIS board--> Lord Almighty
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 is gone! I added it back on, thank god!
5	Create a CD object. Call some of its methods. Can you call the inherited methods(for examplesetComment())? What do you observe about the inherited methods?	The methods are inherited from other classes.
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.	The debugger took me to the item source code.
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 are subclass of fruit cereal, baguette are subclass of class bread chocolate mousse, ice cream are subclasses of class dessert all of these all subclasses of super classes food-item
9	In what inheritance relationship might a touch pad and a mouse be?	touch pad-->mouse
10		square -> rectangle (every square is a rectangle but not every rectangle is a square)
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;
12	Test your answers to the previous question by creating the classes mentioned in that exercise, and trying it out in BlueJ.
13	What has to change in the Database class when another item subclass (for example classVideoGame) is added? Why?
14	Use the documentation of the standard class libraries to find out about the inheritance hierarchy of the collection classes. Draw a diagram showing the hierarchy. http://java.sun.com/j2se/1.4.2/docs/api/
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.
16	Draw an inheritance hierarchy representing parts of a computer system (processor, memory, disk drive, CD drive, printer, scanner, keyboard, mouse, etc.)
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?
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/

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