Obscure Text (Java) - 1.0

Write a graphical utility to disguise or obscure words in a text file. As you have noticed by now, console applications that use the command-line interface and write to the user with System.out.println calls are not very convenient. Take what you have learned about graphical programming while writing games and apply the same to a GUI application that reads from a file, makes some changes to the text, and writes the changed text to a new file.

Input will be changed by replacing lowercase letters ("a" to "z") with random lowercase letters, uppercase letters ("A" to "Z") with random uppercase letters, and digits ("0" to "9") with random digits. Only these characters will be changed, and only on lines selected by the user. Give the user the option of changing every line, every second line, third, fourth, fifth, sixth, tenth, or twelfth line. Give the user the option of selecting lines either sequentially (for example, every tenth line) or randomly with a given probability (for example, one in ten).

Show the changed text in a scrolling output area. Give the user a button to open an input file, according to the options selected. Give the user another button to save the changed text in an output file, and a third button to exit from the application.

Communicate with the user through buttons, options, and messages written into the output text area. You will need a main window ("JFrame") and standard Java dialog boxes to open and save files, but don't use other windows or pop-up dialog boxes -- not even for your error messages. Error or informational messages must go into the output text area or other Java Swing components on your main window. You must handle incorrect user input for the options and possible I/O errors when opening, reading, writing, or closing a file. You may use any Java Swing classes that you need. The sample solution is around 390 lines long and uses (among others): ActionListener, BorderLayout, Box, BufferedReader, FileReader, FileWriter, FlowLayout, JButton, JComboBox, JFileChooser, JFrame, JLabel, JPanel, JScrollPane, JTextArea, Math.random, and StringBuffer.