Assignment 13 - The JPad Text Editor

A Look at JPad 

As you can see, the main JPad window contains:

• a TextArea where you can enter text
• a toolbar with four buttons--New, Open, Save, and Save As
• a menu with one choice, File
• a status area at the bottom that displays "Ready"
• a title bar that says JPad - Untitled

If you drop down the File menu, as shown here, you'll see the same selections that are available on the toolbar, along with the Exit menu item.

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Opening Files

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Displaying Files

Step-By-Step Instructions 

Step 1

Download the starter file, JPad.java to a new directory, compile and run it. If you can't get the program to run, don't go any further; post a message on the discussion board and someone hopefully will respond. [Remember that JPad is an application, not an applet.]

Step 2

Add the menu "hot-keys". Read the menu lesson [Lesson 12.6] if you don't remember how to create a MenuShortcut.

Add the following shortcuts to the menu. [Your changes will go in the menuBar() method].

• File|New - Ctrl+N
• File|Open - Ctrl
• File|Save - Ctrl+S
• File|Save As - Ctrl+A
• File|Exit - Ctrl+X.

To complete this portion of the exercise, you'll have to rewrite the method that creates the menu.

Step 3

Write the newFile() method. Follow the steps shown here:

1. Set the field fname to "Untitled."
2. Clear the TextArea named ta.
3. Set the focus to the TextArea.

Step 4

Write the saveFile() method. Here are the different tasks you need to complete:

1. Check to see if the field fname equals "Untitled."
2. If it does, call the saveFileAs() method.
3. If it does not, call the writeFile() method.

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Step 5

Write the openFile() method. Here are the different tasks you need to complete:

1. Construct and display a FileDialog object. You'll use this, FileDialog.LOAD, and "Open a JPad File" as arguments to the constructor. Set the file mask to "*.jpad" [Instructions on how to do this are in Lesson 13.2]
2. If the user cancels the FileDialog, print a message in the status area [send the Label field status the setText() message], set focus back to the TextArea, and return.
3. If the user did not cancel the FileDialog, assign the directory and the file name chosen by the user to the field fname, and call readFile().

Step 6

Write the saveFileAs() method. Follow these steps, which are mostly the same as those used for the openFile() method:

1. Construct and display a FileDialog object. You'll use this, FileDialog.SAVE, and "Save a JPad File" as arguments to the constructor. Set the file mask to "*.jpad" [Instructions on how to do this are in Lesson 13.2]
2. If the user cancels the FileDialog, print a message in the status area [send the Label field status the setText() message], set focus back to the TextArea, and return.
3. If the user did not cancel the FileDialog, assign the directory and the file name chosen by the user to the field fname, and call writeFile()..

Step 7

Write the readFile() method. Here are the different tasks you need to complete:

1. Check to see if the field fname is equal to "Untitled". If it is, then clear the TextArea, set the focus to the TextArea, and return.
2. Create a FileInputStream using fname as the argument. To do this you first:
   • Create a FileInputStream variable [fis] and set it to null.
   • Start a try block, and call the FileInputStream constructor passing fname as the argument.
3. Read the file. [This code goes inside the same try-block as the code in the previous step.] You can see several examples of this in Lesson 13.2. Here's a simple strategy:
   • Create an empty [""] String variable and an int named ch.
   • Write a while loop that calls fis.read() and assigns the results to ch, until fis.read() returns -1.
   • Cast ch to a char, and append it to the end of your String.
   • [This is where you'll come back and do the "decryption". For right now, leave this as plain text.]
4. Store the results [that is, the String you created in the previous step] in the TextArea using setText(), set the status field to display "File read successfully", and set the title of your JPad window to "JPad - " + fname. [Use the setTitle() method].
5. End the try-block, and write a catch-block that catches Exception. In the catch block, simply print a message in the statusLabel.
6. Add a finally block to close the file. Look at Lesson 13.2 to see how this must be written..

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Step 8

Write the writeFile() method. Here are the different tasks you need to complete:

1. Create a FileOutputStream [fout] using fname. You follow the same steps you did to open your FileInputStream:
• Create a FileOutputStream variable [fout] and set it to null.
• Start a try block, and call the FileOutputStream constructor passing fname as the argument.
2. Create a String variable [s] and retrieve the contents of the TextArea, using getText(). This code is in the try-block used to open the file.
3. Write a for loop that goes from 0 to s.length() - 1. Inside the body of your loop, retrieve each character from your String using the charAt() method. Use the fout.write() method to write the character to the file. This code is also in the try block.
4. Set the status Label to say "File written successfully", and set the title of your window to "JPad - " + fname.
5. End the try block and follow it with a catch block that catches Exception. In the catch block, use the Label status to display an error message.
6. Follow the catch block with a finally block that closes the stream. Look at Lesson 13.2 for an example of how this must be written.

Step 9

Add the Encryption. At this point, you should be able to read, edit, and write regular text files. It's time to add the encryption. Follow these steps:

1. Locate the line in writeFile() that says fout.write(ch). Add 128 to ch when you write it.
2. Locate the line in readFile() that says s += (char) ch. Change ch so that it uses the following expression: ((ch + 128) % 256).

Finishing Up 

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