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1 CS 303, Assignment 10, Background The explanations here are given with reference to the ClickKey application and applet. There are other links on the Web page illustrating 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, which is what is used on the Web page. Notice that sizing the applet is done in the html since it no longer has a frame to size. <html> <title>ClickKey as an Applet</title> <body> Here is ClickKeyApplet. <applet code="ClickKeyApplet.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 the source code and compile it first. .jar files can be used to make these kinds of self-executable files in Java. Follow the directions below to do this. It is also possible to create .jar files 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 see if you have obtained the result that you want. To turn an application into an applet, 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. If it is to be a manifest file, it has to have the extension .mf. The file can have 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: ClickKey It is important to note two things about this: The file name ClickKey does not have 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 results of compilation are sitting together in a single location and that it’s possible to run executables from the Java bin directory in that location, you create the .jar file by entering the following command at a command prompt: jar cfm ClickKey.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, ClickKey.jar, in the same directory. It is important to note that you may have problems running the jar command depending on how Java was installed on your system and what the path is like. 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 to this 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 a 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.
