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1 CS 303, Assignment 9, Background The explanations here are given with reference to the ClickHand application and applet. There are links on the course Web page to several files which illustrate the outcome of the processes described. Turning an application into an applet and putting it into a Web page To turn an application into an applet, take the following steps: 1. import java.awt.* and javax.swing.*. 2. Change the class to an applet by having it extend JApplet. 3. Replace the main() method with an init() method. The contents of the init() method will not be the same as the contents of the main() method. 4. Save the contents of the Frame class constructor for future reference, but otherwise remove this class and all references to it, or machinery associated with it, from the code. 5. Put the code for creating the contents of the frame (panels, etc.), taken from the Frame class constructor, into the init() method. To get the applet into a Web page, you need to have an html file with the correct codes in it. Here is a simple example. This is the html source code you would find in the course Web page for the link to the ClickHandApplet. Notice that sizing the applet is done in the html since the applet does not have a frame to size. <html> <title>ClickHand as an Applet</title> <body> Here is ClickHandApplet. <applet code="ClickHandApplet.class" width="500" height="500"> </applet> </body> </html> 2 Turning an application into a self-executable .jar file It is convenient to be able to group together the components of an application in a single file which can be run without having to open it as source code and compile it first. .jar files can be used to make these kinds of self-executable files in Java. The directions below explain how to do this. It is also possible to create files of the .jar type which serve other purposes. When trying to make a self-executable .jar file, you may accidentally create one of these other kinds of .jar file. Remember to check your results to make sure you got what you wanted. To turn an application into self-executable .jar file, take the following steps: 1. Compile the source code of the application so that .class files are produced. Compilation of a given set of source files might result in more than that number of .class files, depending on how many classes were defined in the source files. All of the resulting class files are needed. 2. Write a manifest file. A manifest file has to have the extension .mf. The file can be given any name. For this example, I used the name mainclass.mf. In the manifest file you specify which class in the application is the main class. The .mf file for this example contains: Main-Class: ClickHand It is important to note two things about this: The file name ClickHand does not take an extension. However, it is followed by a new line. The .mf file won’t work correctly if its contents are not followed by a new line. 3. Assuming that all of the class files resulting from compilation are sitting together in a single directory and that it’s possible to run executables from the Java bin directory from that location, you create the self-executable .jar file by entering the following command at a command prompt for that directory: jar cfm ClickHand.jar mainclass.mf *.class If desired, it would be possible to list all of the class files rather than using the wildcard expression *.class. The successful outcome of this command is a new file, ClickHand.jar, in the same directory. You may have problems running the jar command depending on how Java was installed on your system. It is possible that it won’t run from the directory where you have compiled your application. One solution to this problem is to try and fix the path. The quick and dirty solution is to copy all of the needed files into the bin directory of the Java installation on your computer. This is where the jar utility is located and it will run from a command prompt in the bin directory. The shortcoming of this solution is that you clutter up the Java program directory with your files and you have to be careful when cleaning up so that you don’t delete any of the Java system files.
