.Open CS320: First Java Laboratory
. Check out New things on the Course Web Page
.See http://www.csci.csusb.edu/dick/cs320/
. Goals
Your task is to try some the experiments on this page.
. Deliverable
Write notes on three experiments and include links to the code.
If the experiment includes an applet then embedd the applet in your web page.
. Browser
In JBH358 the Firefox browser has the Java plugin loaded. Use the command
.As_is firefox
in a terminal window to run this browser.
. Hints
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Keep your Java handout handy.
Put an applet called AaAa in file AaAa.java not in a file called aaaa.java.
See
.See http://www.csci.csusb.edu/dick/samples/java.html
and
.See http://ftp.csci.csusb.edu/public/faculty/dick/
.Close.Box
. Demonstration 1
Here
.See http://ftp.csci.csusb.edu/public/faculty/dick/test.Goodbye.html
is a simple Java `applet` in an HTML page. The page also has links to
the Code I wrote, the documentation, and `bytecode`
that I prepared from it. Follow the links to the
Source code, Documentation and Byte Code.
You can use this page as a model for your own examples of Java Applets.
. Demonstration 2
Here
.See http://ftp.csci.csusb.edu/public/faculty/dick/test.Henrici.html
is a demonstration of something that was easy to program in
Java. Have a look at it.... the graphic is produced by the
Java `applet` in the HTML page. You can also follow the two links
to the Java source code and to the documentation generated by the
source code.
Note. You don't have to understand why this picture is called an
Henrici spiral or what the mathematics means. Its just a formula
that generates rather nice looking graphics -- enjoy it.
. Your First Java Program
Here you will need to have two windows working at one time: One running
a browser (say `Netscape` on your workstation) and the other to edit, compile, and
run commands in the Java Development Kit(JDK). The various versions
can be listed by inputing the UNIX command into a command/terminal window:
.As_is ls -ld /share/j*
Different machines seem to have different relaible ones so you may
have to try out several below.
In your browser window look at this:
.As_is import java.lang.*;
.As_is public class Hello {
.As_is public static void main(String argv[]){
.As_is System.out.println("Hello, World!");
.As_is }
.As_is }
It is a traditional first C program written in Java. Perfect
for experimenting with the compilers and JVMs.
Use your favorite editor to create a copy
of the program above in a file called.
.As_is Hello.java
Notice: not `hello.java`, not `h.java`, but `Hello.java`. This is important!
Compile it like this:
.As_is /share/java1.4.1/bin/javac Hello.java
or perhaps
.As_is /share/j2sdk1.4.1/bin/javac Hello.java
Note: Do not hold your breath waiting for this to compile, the compiler
was very slow when I tested it.
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If the above worked you now have a file called 'Hello.class'. It is
a binary file. Do not try editing or listing it!
If the 'javac...' doesn't work you may have a typographical error...
First check that you did type '.../javac Hello.java' as shown. Then try
downloading
.See http://ftp.csci.csusb.edu/public/faculty/dick/Hello.java
as Source into a file called "Hello.java" and try again.
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Run the compiled class like this:
.As_is /share/..../bin/java Hello
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Notice
'java Hello.java' and 'java Hello.class' do not work!
The `source` is compiled, but a `class` is interpreted.
Java code was designed to be interpreted by a
machine independent `virtual` machine that runs bytecode.
bytecode::=http://www/dick/samples/java.html#bytecode.
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. Your Second Java Application
Modify your Hello.java program -- using your favorite editor --
to output a message with your name on it.
(use the same name for the file and the class)
Then try out my `quickie` or `Q` program to compile,
document and run your program.
.As_is Q Hello.java
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I named the program Q for a character played by John De Lancey in
`StarTrek: The Next Generation`, my `Q` program is almost as
quirky and powerful.
If your shell reports that 'Q can not be found', then you can
.List
Use
.As_is ~dick/bin/Q Hello.java
instead.
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. Demonstration of Polymorphism in Java Application
In the class we met a simple example of polymorphism in
Java
.See ../15q.java
and in C++
.See ../15q.cpp
download these files as source, save them, compile them and make
the C++ program do the same thing as the Java application.
. Your First Applet
Your task is to construct a public WWW page that has an applet
that displays some text. The name of the page is:
.As_is test.HelloWorld.html
and it should contain the following HTML:
.As_is Test Hello World
.As_is
.As_is
You now need a file called:
.As_is HelloWorld.java
containing
.As_is import java.applet.*;
.As_is import java.awt.*;
.As_is public class HelloWorld extends Applet {
.As_is public void init() {
.As_is setSize(150,25);
.As_is }//init
.As_is public void paint(Graphics g) {
.As_is g.drawString("Hello world!", 50, 25);
.As_is }//paint
.As_is }//HelloWorld
The Applet is compiled just like any other program:
.As_is /share/java1.4.1/bin/javac HelloWorld.java
This will generate a file with "HelloWorld.class".
Notice that the compiler forces you to name the file
.As_is HelloWorld.java
and the class in the file must match
.As_is HelloWorld
and be `public` for it to be used over the World Wide Web.
You can view this file with a browser..... BUT
make sure it is Netscape 6.* not 4.* on your workstation.
Or else try Konqueror or Mozilla (and turn on the Java and
console). Konqueror need to know where to find the 'java' JVM as well!
Before others can access your work you must
copy all the *HelloWorld* files to
your public directory we will worry about this in a later!
Note
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Java is supposed to offer: Write Once, Run Anywhere.
What you get is: Write once, Debug Everywhere
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. A Second Applet
Your next task is to change your HelloWorld.java program
to output the result in color by adding
.As_is g.setColor(Color.blue);
to HelloWorld.java. Compile and then
publish to check the result. Make sure you shut netscape down
and restart it.... otherwise you'll probably get the OLD cached
version:-(
Next change the font in your graphic:
.As_is g.setFont(new Font("Helvetica", Font.BOLD, 24));
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If your browser doesn't show your Applet... Look under Netscape's Option
menu and set the "Show Java Console" option. This will show any errors
and also any System.out messages.
Netscape does not make a useful tool when developing Java
applets for one simple reason. Netscape does not want to reload your
Java Applet's compiled code. The reload button makes no difference!
Sometimes a SHift or Control click on the reload button may work.
Personally I include a test harness in the class itself, as
follows.
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. An Application that runs an Applet!
An application is a class with a 'main' function. An Applet
needs a graphic window to run in..... so if we write a
main function for HelloWorld that creates a graphic window then
it can run the Applet. Get a copy of this:
.See http://ftp.csci.csusb.edu/public/faculty/dick/HelloWorld.java
and compile and test it like this:
.As_is javac HelloWorld.java
.As_is java HelloWorld
Once this runs ok, change the color and form of the graphic string.
Make the result run.
.Box
Adding a suitable main function is a viable development technique. However
Java does not make it easy to add a function to a class.
It is worth keeping 'main' in
a special file and learning how to read files into Java code
using your favorite editor.
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. Publishing Your Applet
Don't forget that you must always publish the *.class files for
all Applets on your web pages... and all the classes that they call.
You should always make the documentation available on any class you publish
so that others can use it. In this class you also need to publish the
source code so that It can be graded! You should have noticed
that my favorite technique for Applets
is to add links to a published test page that links to the source code.
Edit test.HelloWorld.html so that is has a links to the Source code
and documentation
after the end of the applet:
.As_is Source Code
and publish all the files by copying them `all` to your public directory:
.As_is cp *HelloWorld* /www/public/..../
or
.As_is cp *HelloWorld* /web/public/..../
(depending where your public WWW/Web directory is).
Now use Netscape to look at the page... Follow the links to the code
and then to the documentation, and from there to the documentation
on String.
. Earn credit for the lab
Write up your experience in a new CS320/java page or (if it works)
on your test.HelloWorld.html page. You can get full credit for
programs that run in private in this lab.
.Open Extras
. A Silly Application
This is an application that was used to teach me what a loop
was, back in the 1960s. It also shows how Java Input/Output
works.
The documentation for the "Luv" example is at
.See http://ftp.csci.csusb.edu/public/faculty/dick/Luv.html
Study the documentation a bit before you get your own copy of
the source code
.See http://ftp.csci.csusb.edu/public/faculty/dick/Luv.java
Compile and test the application.
. A Modern Version
These days users expect to point and click rather than input
text to answer questions. To see how the previous program looks
as an event-driven applet follow this link:
.See http://ftp.csci.csusb.edu/public/faculty/dick/test.Luv5.html
While you are there follow the links to the Code and Documentation.
.Close Extras
. Setting your UNIX up for Java
Make sure your PATH variable has /share/java1.4.1/bin or else
/share/j2sdk1.4.1/bin added to it when you next plan to
use Java.
To add /share/j2sdk1.4.1/bin to your UNIX shell PATH
.Net
edit your ~/.bash_profile file so that the
PATH is redefined precisely like this
.As_is PATH="$PATH:/share/j2sdk1.4.1/bin"
.As_is PATH="$PATH:/share/bin"
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This is reread whenever you login or open a terminal window.
Test it before you logout by executing
.As_is . ~/.bash_profile
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. Glossary
Application::java=`a normal program that is executed on its owner's machine`.
Applet::java=`a program that can be sent accross the web and executed inside a web page on a remote user's computer`.
Polymorphism::jargon=`In a polymorphic language a pointer declared to point at a high level object can point at a low level extension and get the extended behavior`.
.Close CS320: First Java Laboratory
. Check the Preparation for next class
.See ../16.html