Rather than waste connection time reading this stop press it might be worth saving it to a file using your browser.

Subscribing to the M874 mailing list

The course maintains an email mailing list for each of its presentations, and we strongly recommend that students subscribe to this list. We use it to send notification of Web site updates and other news. Once you register for the course, you will have access to the web site for your course presentation, and you will be able to subscribe to the list from the Stop Press page.

Errata

There are two sets of errata on the course: serious errata and typos.

Submitting TMAs

All the TMAs in the course involve you carrying out a large amount of programming. We ask you to supply a machine readable version of your code together with a printout of the code and any associated HTML files. The preferred method for doing this is by sending the code on a floppy disk together with the printout and your PT3. We are also happy for you to send your code via email. However, it is worth making a number of points about this:

• Before sending any code email your tutor with a test message containing a file in order to check that both your mailers can transfer text files. We would ask you to send the files as attachments to your email, rather than placing them in the body of the email.
• Each TMA will specify a directory structure for your files, please use it.
• On the day you send the email, post the hardcopy of the emailed code to your tutor together with the PT3. Do not be tempted to use email to gain a few days extra time by doing some further work on the code and then sending it a few days later than the hardcopy. We have told tutors that the receipt of the hardcopy marks the formal submission of the TMA and if they find any deviations in the emailed code from the hardcopy version then 60% of the marks are to be deducted.

Submission on MZX874

If you register for the electronic version of this course, MZX874, you should follow the instructions in 'Using the Electronic TMAs System' which you will receive in the second mailing of course materials. You may submit your eTMAs to the eTMA Web site or to the eTMA email address.

Please note that you will need to submit:

1. Your code files set out in directory structure specified in the TMAs on this Web site.
2. A text file containing all the code which will be marked by your tutor using the electronic marking tool. The marking tool cannot be used with the Java files.

Sun Java Certification

Sun, the developers of the Java language have developed a Professional Certification Scheme for programmers with a knowledge of Java.

The course team have examined the 55 examination objectives for the certification and are confident that most of these are satisfied by the study of M868 and M874. The objectives that we feel you need to read further on and practice via programming are the six below:

• Identify the earliest point in a method at which the object referred to by a local variable becomes eligible to be garbage collected, in the absence of compiler optimisation.
• Define the conditions that might prevent a thread from executing.
• Write a code to implement the paint () method of a java.awt.Component class. Describe the interactions between the methods repaint () and update ().
• Recall the type and significance of the return value from the handleEvent () and action () methods of the java.awt.Component class.
• Identify the return value of an overridden handleEvent () or action () method to control propagation of the event up the container hierarchy. Select from a list valid reasons why an event might be passed up a container hierarchy.
• Write code that constructs "chains" of InputStream and OutputStream objects using the subclasses of FilterInputStream and FilterOutputStream. Select from a list the valid constructor arguments for FilterInputStream and FilterOutputStream subclasses.

More Useful Links

Individual sites

There are a number of sites maintained by individuals which contain the latest Java trawlings from the Web, pointers to tools, tutorials and articles. A selection is shown below:

• John December's Java Online Information Sources.
• The JavaSecurity Hotlist.
• Elliotte Rusty Harold's "Cafe au Lait".
• Dave Central Software Archive.

Java directories

There are a number of directories which contain lists of Java resources. These are listed below:

• Yahoo Java Collection.
• Earthweb's Gamelan Directory.
• ACM's Virtual Library of the Java Language .

Tutorials

A number of tutorials on Java have been set up. A list of these is shown below:

• Sun's Java Language Tutorial.

Book listings

There are a number of independent book listings which have been set up. Three are listed below. The last one provides a navigable way to find your way through the large number of Java books that have been published.

• BeaconRay's Java Bookshelf.
• smartbooks.com.

Security problem

If you are accessing this web site from your work and your system administrator has erected a firewall or similar device around your network to prevent applets being read into your browser, then you will find that you will not be able to access the computer mediated questions. Currently there are only two solutions to this: either persuade your system administrator to modify the policy (admittedly unlikely) or try and access the Web site from an unconstrained browser.

Installation check

Before starting the course it is worth checking that the installation of the Java system has worked. First check that the MSDOS command line window points to your M874Programs folder. You will see this on the prompt line in the window. If you do not see it you will have to carry out the following procedure:

1. Find your MSDOS program (it may be a shortcut on your desktop).
2. Right click on the MSDOS program and select Properties, a tab dialog will be displayed.
3. Click on the Program tab.
4. In the Working field type in C:\MyDocuments\M874\M874Programs.

After you have done this check that your system recognises the Java system software. All you need do is to type the line Java to the MSDOS prompt and you will see a long multi-line message starting with a line which commences with usage Java. if you see this line then everything is fine. If not you will have to carry out the following procedure:

1. Open the Pfe32 editor which we have provided and edit your autoexec.bat file. This can be found at the top level in c:.
2. You should edit the SET PATH line to add ;\MyDocuments\M874\java\bin to the end of the line, don't forget the first character which is a semi-colon.

Weekend schools

The CCI programme organises short schools on each course in the programme. These are held at a number of university locations around the country. They normally take place towards the end of a course and provide an excellent opportunity for revision. We are providing a package of material for tutors who will be teaching at M874 schools. . Tutors will base their sessions on the material that we have produced; however, we are giving them the freedom to modify the materials as they see fit.

The package will contain:

• A set of Powerpoint slides which cover the main topics of the course.

• A set of exercises in the same format as that found on the course CD.

• A sample examination paper different to the one which is provided for you in the course mailing, together with a set of slides which take you through the answers to the paper.

You can download the slides to your own computer if you have Powerpoint installed. This is not an official part of the course, so regard it as an add-on. You can download:

• A plain white background version (395kb) of the slides and notes.Load this if you do not have unzip facilities.

• A glitzy version (400kb). You can play this as a slide show and use the notes as, say, revision. Load this if you do not have unzip facilities.

• A zip file of both version (166kb) of the slides and notes.

The exam presentation consists of around 45 Powerpoint slides which look at typical examination questions and answers. There are two versions of these slides. If you have unzipping facilities then there is a zipped version (19kb). If you do not have zipping facilities then there is a raw version (90kb).

We are grateful to Robin Thomson, a tutor on the course, for the information that a free Powerpoint viewer can be downloaded fromMicrosoft. You can use this to view the slides for the two-day school presentation and also the slides for the two day school session on the M874 examination.

Pfe32 Hint

The Pfe32 editor contains a facility whereby you can, within the editor, bring up a DOS command line and execute it. You might find this useful when editing and compiling a Java program. The Execute menu contains a DOS command to Window item (F11) as its first pull down. When you activate this item it will ask you for the name of the command. Type in java followed by the name of the file you are currently editing. In the same dialog you will need to change the directory that the editor points to to M874Programs. After this all you need to do to syntax check and compile a file is to activate the Execute menu and pull down and release the Repeat DOS Command to Window item.The output from the command will appear as a window in your editor.

A Note on the use of integrated development environments.

Some students have asked about their use of IDEs such as Visual J++ and Symantec Cafe. We have no objection to their being used. The only point that we would want to make is that they use absolute layout schemes to layout the widgets of an interface. We want you to use the portable layout managers such as GridLayout in your work and, in particular, in your TMA answers. Most IDEs allow you to switch into these layout mangers so there should be no problems.there is alos a further problem with Visual J++ as it only uses the java 1.0 event model and we use the 1.1 event model on the course.

Some of you may not understand this point until later in the course when we deal with HCI, it is worth filing this note away until then.

A note on this

There have been a number of student questions about the use of this. When this is used outside a constructor it is normally used to refer to the instance variables within the destination object. For example, if you had a class which had two instance variables x and y and you had a line of code in a method which referred to them, say in assigning some values to them as in

x = 2; y =3;

then this is equivalent to writing

this.x = 2; this.y = 3;

In this context this refers to this destination object. Normally unless we want to explicitly draw attention to the fact we are referring to the instance variable we omit the this.

A note on == and equals

There seems to be a little haziness about the difference between = = and equals. The former can be used to compare scalars or objects. When it is used to compare scalars it carries out a comparison on their values, when it is used to compare objects it compares addresses. The method equals is used to compare the equality of objects. All the classes in the Java API have equals already defined. However, if you have developed a new class and need to carry out some equality comparison of the values of objects defined by the class then you will need to define a method equals for that class. Normally the code for this method carries out some element-by-element equality comparison of the instance variables: for instance variables that are objects then an equals message is sent to them and for scalars = = is used. Not understanding the difference between = = and equals leads to some very subtle programming errors, so be awake.

Possible problem with Netscape and Exercises 2.10 and 3.5

There is a possible problem with the Netscape browser and these two exercises. In exercise 2.10 you are asked to click on the top-level documentation. This link may not work in Netscape. In exercise 3.4 you are asked to click on the Top page of the Java documentation and on index, these links may not work.The best solution is to use your browser to open the file java/api/packages.html in the JDK version that we sent you and to add this link to the favorites collection for your browser.

Browsers and applets

Whenever a new version of Java is developed the browser manufacturers take their time in catching up. This slightly affects the exercises in the course which ask you to develop applets: snippets of HTML which contain Java code. Currently Internet Explorer 4.0 is 99.99 percent compatible with Java and Netscape 4.04 onwards is compatible with a patch which can be obtained from the Netscape site. If you want details on upgrading your browser to Java 1.1 then a tip in Java World provides this information. If you do not want to upgrade, then the JDK 1.1 kit supplied with the course has a program known as the appletviewer. This is initiated by using the MSDOS line and referencing the html file containing the applet. What this program does is to strip off all the html code from the file and just executes the applet in the file. The pages which are provided for you on the course CD and on this Web site can be accessed by any Java 1.0 compliant browser.

The course supplied JDK and TMAs

In each of the TMAs we stress that whatever version of Java you use, or whether you use an IDE, you should compile and run your Java code using the JDK version supplied with the course and check that it works. If you don't and your code does not run on your tutor's machine then you will be penalised.

Checking your system for TMA03

TMA03 requires you to develop a server and a client which interact with each other. In order to do this they use sockets and server sockets which are based on the TCP/IP protocol. It is worth checking that your system can handle this form of communication. In order to do this we have provided you with two programs. The first is a simple client which sends a single test string to the second program which is a server. The server reads the test string and then displays it on the MSDOS line, it will sleep for five seconds and then return you to the MSDOS command line. We have built in this delay in case some of you are using an Integrated Development Environment (IDE) which collapses the MSDOS window when execution finishes preventing you from reading the output.

The tasks that you should carry out to check everything is working for TMA03 are:

1. Compile both programs.
2. Open an MSDOS window and execute the server program. It should just sit there after displaying "Server started waiting for client".
3. Open another MSDOS window and execute the client program. This will quickly terminate.
4. Now look at the MSDOS window for the server it should now display the messages "Test message sent OK" and "5 seconds to finish". After five seconds the MSDOS command line prompt will appear, if you are using an IDE the window may then disappear.

The programs are shown below, as well as checking your system they provide you with examples of the two streams that it is best to use for client, server communication: BufferedReader and PrintWriter. The server is:

import java.net.*;
import java.io.*;

public class SimpleServer {

public static void main(String args[]) {
Socket s=null;
ServerSocket ss=null;
BufferedReader br = null;
try{
  ss = new ServerSocket(1024);
  //Blocks waiting for the client
  System.out.println("Server started waiting for client");
  s = ss.accept();
  br = new BufferedReader(new InputStreamReader(s.getInputStream())); 
  System.out.println(br.readLine());
  //Code below sleeps for 5 seconds
  //just in case student uses an IDE which destroys 
  //the MSDOS window automatically
  System.out.println("5 seconds to finish");
  try{
    Thread.sleep(5000);
  }
  catch(Exception e){};
  s.close();
  ss.close();
  br.close();
}
catch(IOException iExc){
  //You have a problem
  System.out.println("Problem with connection");
  iExc.printStackTrace();
  }
} 
}

The client is

import java.net.*;
import java.io.*;

public class SimpleClient {

static public void main(String args[]) {
Socket s = null;
PrintWriter ps = null;
try{
  s = new Socket("127.0.0.1", 1024);
  ps = new PrintWriter(s.getOutputStream(), true);
  //true ensures autoflushing
  ps.println("Test message sent OK");
  ps.close();
  s.close();
} 

catch(IOException iExc){
  System.out.println("Problem with client connection");
  iExc.printStackTrace();
}

}

}