02115   Java Programming
Autumn 2011

Preparations for the week

The variable d2 will refer to an instance of class D2 thus defining its dynamic type. The details are as follows (refer to the last seven lines of page 28 in the PS textbook):

1. The field f of the D2-instance is initialized to the default value 0
2. The constructor of the superclass D1 implies an application of method m2()
3. Method m2() prints out D1.m2   and then applies method m1()
4. Because method m1() of class D1 has been overriden in the subclass D2 the method m1() of class D2 will be executed because the dynamic class type of d2 is D2
5. The execution of m1() from class D2 prints out D2.m1:0. The value 0 is the default value given to f previously
6. At last the assignment f = 7 from the constructor D2() gives f its final value

The lectures of the last week has covered most of the Chapters 8 and 9. And if you have followed up by working through the text as told in the section After the lectures on the last Week plan you have become familiar with the concepts and are able to use them.

On page 291 a reference was given to Joshua Bloch's Effective Java, a textbook which I strongly recommend. I was not able to look up sample chapters of the book on the net, but I have the printed book.

Before buying the book mentioned above just take a look at the paper   Java performance   written by Peter Sestoft and referenced at the course home page link to Some Java supplement. The paper gives some advices on improving the execution of Java programs.

Do you think a class can inherit from more than one superclass ?
In the textbook PS section 9.5 (page 22) the form of an extends-clause is described by

      class C extends B { ... }

and we are told, that class C is a subclass and hence a subtype (section 5.5) of B. And from that we can judge, that it does not make sense if a class should be a subtype of two or more probably independant super classes.

Thus: A class can only have one super class.



The BlueJ environment has surprised me when I put a new BlueJ project on the subpage 'Some BlueJ projects': I just defined a project consisting of the two files from Example 27 and Example 28 of the PS textbook (page 23) without spliting up Example 27 into four separate files.
Try to save the .jar, and then compile and run the main() method from within BlueJ.



The Chapters 10 and 12 present important concepts and very useful Java constructs to be used by the experienced programmer.

Chapter 10 introduce abstract classes and interfaces and thus gives the full background for understanding the description in the PS textbook on collections, refer to the overview on page 92. Chapter 12 introduce the SortedMap interface and the concrete classes TreeSet and TreeMap.

As an introduction to this week, prepare yourself by study the BK textbook to the following extent:

1. Chapter 10: 10.1 - 10.2.4; pages 300-314:
   • Read the chapter introduction and section 10.1, pages 300-301 to get an overview.
   • Read section 10.2 - 10.2.4, pages 301-314, to be introduced to the foxes-and-rabbits simulation project.
     Some of the exercises below lead you to analyse how close the simulation model is to real-life.
     Work through the exercises 10.1 - 10.6, 10.10 - 10.11, 10.13, 10.14 and 10.16
2. Chapter 12: 12.1 - 12.3; pages 381-393:
   • Read the chapter introduction, pages 381-382, to get informed on the main purpose of the Chapter, that is to anticipate and respond to error situations.
   • Read section 12.1, pages 382-386, to be introduced to the address-book project.
     Work through the exercises 12.2 - 12.4
   • Section 12.2, pages 386-389, pay attention to the idea of foreseeing errors and how to react.
     Work through the exercises 12.8, 12.9 and 12.14
   • Section 12.3, pages 389-393, introduce simple ways of reporting errors from a server to a client in order for the client to minform the user.
     Work through the exercises 12.16 and 12.20

The lectures

But many subjects of the chapters are left for personal studies.

Exercises at the PC's

• Chapter 10:
  Exercises 10.38 - 10.42
  10.47 and 10.48
  10.60 and 10.62
  and (for the more experienced student) 10.45, 10.46 and 10.52 - 10.54
• Chapter 12:
  Exercises 12.24 - 12.25
  12.26 - 12.27 and 12.29
  12.31 - 12.32
  

After the lectures

At the end of this week you are supposed to be familiar with the following parts of the BK textbook:

• Chapter 10: Pages 300-336. Also remember to read pages 334-335 with the Summary, including the terms and the Concept summary in order to check that you are familiar with what has been introduced in the chapter. If some terms and/or concepts are not familiar to you, then look up the descriptions in the chapter.

  In the Sections 10.1 and 10.2 (pages 300-316) focus on how the solution is structured and build up by use of many classes and study how the jobs are delegated out.

  Sections 10.3 and 10.4 (pages 316-324) introduce abstract classes and abstract methods. As an easy-to-read introduction just start with Example 27, page 23 of the PS textbook:

  • The method capacity() of class Vessel has to be abstract because the value it should return depends on the specific shape of each kind of vessel.
  • In the classes implementing the method capacity() one takes advantage of the fact that a cube is a special proportioned tank.

  Sections 10.5 and 10.6 (pages 324 - 334) are dedicated to multiple inheritance achieved by use of interfaces. The subsections 10.6.2 and 10.6.3 (pages 330-331) illustrates the precise description of section 13.2 in the PS textbook (page 60). Also read the Examples 85 and 86 on page 61.
  Subsection 10.6.4 settles the most important characteristic of interfaces to be that they completely separate the definition of the functionality from its implementation.

• Chapter 12: Pages 381-406. Don't forget to read the chapter introduction .
  • When going through Secion 12.1 (pages 382-386) open the address-book-v1t and look at each class (by use of the editor) in order to judge about the chosen class structure.
    Would it be an improvement to use an enumerated type ?
    Refer to section 7.13 (pages 233-237) and to PS section 14 (pages 62-63)
  • Sections 12.2 and 12.3 (pages 386-393) introduce error checking and error reporting.
  • The principles of throwing exceptions are described in Section 12.4 (pages 393-399). An exception classes oveview and usefull details are presented in subsections 12.4.2 - 12.4.5 (pages 394-399)
  • Section 12.5 (pages 399-405) go over how to catch and handle exceptions in Java by use of the try...catch mechanism. The statements whose execution may cause an exception to be thrown should be placed in the try branch and the handling of the exception should be placed in corresponding catch branches with one branch for each kind of exception.
  • Section 12.6 (pages 405-406) shows how to implement personal Exception classes which has to be declared to inherit from the standard Exception class.

• Section 7.1, the first two pages, pages 12-13
• Section 8.2, pages 16-17, including Example 20
  An array initializer holding expressions of type String should be used as argument when a main() method is applied from within the BlueJ environment
• Section 9.7, page 24, on the member access modifiers private, protected and public
• Section 9.8, page 26, the first 4 and the last 5 lines about the throws-clause
• Section 9.10, page 28, read about the use of throws-clause in relatíon to constructor declarations
• Section 15, pages 64-65, including the two examples.
  Relate the exception class hierarchy to Figure 12.1 in BK on page 395
• Sections 12.6.5 and section 12.6.6, pages 56-57, including the two examples Example 80 and Example 81
• Section 22.6, pages 100-101, including only Example 128, but leave out the last three TreeMap constructors on page 100
• The first 17 lines of section 24 (page 134) give the background for understanding the use of a Map<Class, Color> colors in the class SimulatorView (open the editor on that class using the foxes-and.rabbits-v1 project) to hold information of the colors used in Figure 10.2 (page 303) of the BK textbook. Primaryly, refer to the first sentence of section 24.1 of the PS textbook.
  The colors are set by the method view.setColor() on page 312 of BK. As keys are used Rabbit.class and Fox.class, respectively, and the corresponding values are the colors Color.orange and Color.blue, respectively