GUI, Events and Applets from Applications, Part III

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Dustin Holland
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1 GUI, Events and Applets from Applications, Part III Quick Start Compile step once always javac PropertyTax6.java mkdir labs cd labs Execute step mkdir 6 appletviewer PropertyTax6.htm cd 6 emacs PropertyTax6.htm & cp../5/propertytax5.java PropertyTax6.java Submit step emacs PropertyTax6.java & submit csc156abc 6 Problem Statement and Specifications This is not so much an exercise in programming as it is in converting an application (the type of program that we have been writing all along with a main() method) to an applet (the type of program that can be executed on an Internet accessible page by any qualified user and will have an init() method). One of the primary advantages of Java is its ability to navigate the Internet. There are a few simple steps that can take any Java application that performs input and output with GUI based utilities and convert it to a Java applet that performs the same calculations, input and output. Assignment 6 Statement: Convert the application PropertyTax5.java to an applet named PropertyTax6.java that performs identical functionality and appearance of the form. The applet will require the use of a HyperText Markup Language (HTML) file that should be named PropertyTax6.htm. Use the appletviewer command to preview your applet. The HTML language is the basis of virtually every page of data on the Internet. It was originally developed at the CERN Laboratory for Particle Physics in Geneva, Switzerland by Tim Berners-Lee as a means of sharing documentation amongst remote researchers using common tools. The latest versions of the language can be found at World Wide Web consortium. There are some tutorials available at this site. We ll use a minimal set of these commands for our purposes that we ll document at this point. In general, every HTML file should be named with an extension of htm or html. So, the Internet accessible file foo would be named foo.htm or foo.html. We ll assume that we re always using the htm extension for our files. Each of the markups that we re using determines a field of the page that begins with the markup and ends with a markup of the same name preceded by the slash (/) character. For example, the field determined by the <abcd> markup ends with the </abcd> markup. 1

2 Assignment 6 Specifications: Process In the file PropertyTax6.java import the the appropriate packages Use inheritance to make the class a subclass of JApplet Update the class and the constructor method name Replace the main() method with the init() method Remove the unnecessary methods that support display options setvisible() setsize() settitle() setdefaultcloseoperation() Process In the file PropertyTax6.htm Code the HTML markups to support the applet <html> <head> <title> <body> <applet> Object Analysis and Algorithmic Development The conversion process from a GUI application to an applet does not really require changes in algorithmic development if we want the applet to exhibit the same functionality that the application did. There are some modifications that we ll need to implement in the source file for our applet to run, and we ll need to code the HTML file to support the applet. We ll begin by discussing the HTML tags that are necessary to run the applet. Note that steps in blue represent lines of code that you should author to complete the assignment. The <html> Markup The <html> markup should be the first markup used in every HTML file. The file should end with the </html> markup. All other markups should reside within the field determined by these markups. The <head> Markup The <head> markup represents a field for all the head elements. Elements inside <head> can include scripts, instruct the browser where to find style sheets, provide meta information, and more. The <title> Markup The <title> markup defines the title of the document and is required within the <head> </head> field of all HTML/XHTML documents. The title field defines a title in the browser toolbar, provides a title for the page when it is added to favorites, and displays a title for the page in search-engine results. The <body> Markup The <body> markup defines a field that represents the visible area of the document. The <body> field follows the </head> tag and contains all the contents of an HTML document, such as text, hyperlinks, images, tables, lists, etc. 2

3 The <applet> Markup The <applet> tag defines an embedded applet in the HTML argument. Important options include width and height that define the size of the window that the applet will execute within. In addition, the code option is required as it identifies the.class file of the applet. Figure 1 represents the necessary HTML code for the file PropertyTax6.htm for this assignment. <html> <head> <title> PropertyTax6 Applet </title> </head> <body> <applet code = "PropertyTax6.class" width = "400" height = "300"> </applet> </body> </html> Figure 1: Lab 6 PropertyTax6.htm Coding for Compilation Logon to your csc.oakton.edu account and create a new subdirectory of the labs directory called 6 to work on your assignment. cd labs mkdir 6 cd 6 You ll need to code the HTML in the file PropertyTax6.htm that is displayed in Figure 1. Issue the following command and type that code into the file. emacs PropertyTax6.htm & Now, we ll need to start the conversion of the application in the file PropertyTax5.java to an applet in the file PropertyTax6.java. We can begin to do this with the following commands. cp../5/propertytax5.java PropertyTax6.java If you need to, return to the Assignment 5 solution and execute the application sufficiently many times so that you can determine that your converted applet will have identical appearance and functionality. When you are ready to move on, issue the following command to start the conversion process. emacs PropertyTax6.java & Examine the contents of PropertyTax6.java as compared to our discussion above. We ll list the specifications and discuss the modifications that are necessary to covert the application to an applet. 3

4 import the appropriate packages The only package that is necessary to support the JApplet class is that class itself. It can be made available to your program with the following import statement. import javax.swing.japplet; Use inheritance to make the class a subclass of JApplet Since GUI applications are a subclass of JFrame, all that we need to do is replace the class JFrame with the class JApplet in the class statement. Having done that, we will no longer have the need for exit criteria from the JFrame. We ve done this with JButtons that are appropriate for applications, but those techniques should probably not be used with applets. We need to give the user the ability to shut down their application and close their JFrame object with a JButton but to do so with a user s browser session is probably presumptuous. Many users have multiple browser windows active and the need to shut all of them down when they re done with one applet is highly unlikely. For this exercise, you can simply ignore the exit JButton. Update the class and the constructor method name We ve changed the name of the file from PropertyTax5.java to PropertyTax6.java so this will now need to be the name of the class. This change can be made on the class statement. In addition, this class has a constructor by the name of PropertyTax5() that will need to be changed to PropertyTax6(). Finally, this constructor is invoked in the main() method, so by changing the name of the constructor to PropertyTax6(), we ll need to change the name of the method that is being invoked in the main() method to the same name. Replace the main() method with the init() method This consists of simply replacing the main() method in the class with the init() method. Remove the unnecessary methods that support display options Due to the lines that have been coded into the PropertyTax6.htm file, there is no need for the method invocations setvisible(), setsize(), settitle() or setdefaultcloseoperation() in the file PropertyTax6.java. These lines should be removed from that file. Checkpoint Save your program to disk by choosing the Save command from the Files menu of your emacs session. Then, compile your program by choosing the Compile... command from the Tools menu and change the make -k that is displayed to javac PropertyTax6.java. Compiler errors can be parsed with the keystroke C-x and need to be repaired before your program can execute. When your program has compiled, click on your xterm window to access your command line prompt, and issue the following command. appletviewer PropertyTax6.htm The output and functionality should be identical to that which was exhibited for PropertyTax5.java except for the use of the exit JButton. If not, you should ensure that your HTML file is identical to Figure 1 and that you ve faithfully followed the steps discussed above. There is a correctly function version of the program for PropertyTax6.java at this link. 4

5 Printing and submitting Once you are satisfied with the correctness of your program, print it as you did with previous assignments by using the following command that assumes that you are working in the room 1234 at Oakton. Retrieve your copy from the printer. printer 1234 PropertyTax6.java printer 1234 PropertyTax6.htm Finally, submit your program with the following command that assumes that you are registered in section abc of CSC 156. submit csc156abc 6 5

Graphics User Defined Forms, Part I

Graphics User Defined Forms, Part I Quick Start Compile step once always mkdir labs javac PropertyTax5.java cd labs mkdir 5 Execute step cd 5 java PropertyTax5 cp /samples/csc/156/labs/5/*. cp PropertyTax1.java