Application for encrypting and decrypting files in Java

(See the next iteration.)

I have that application for en-/decrypting files. Here, I will post the actual GUI and command line code. In order to run the program refer to this GitHub repository.

Some images:

My code is as follows:

App.java:

```
package net.coderodde.ciphertool;

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.Toolkit;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
import net.coderodde.encryption.CipherTools;
import net.coderodde.file.FileTools;

/**
* This class implements the command line app for encrypting and decrypting
* files with a key.
*
* @author Rodion "rodde" Efremov
* @version 1.6 (Feb 29, 2016)
*/
public class App {

private static final String HELP_MESSAGE =
"Usage: java -jar File.jar [-e | -d FILE1 [FILE2 [...]]]\n" +
"Where -e encrypt the files.\n" +
" -d decrypt the files.\n" +
" the key in decimal; " +
"use prefix \"0x\" for hexadecimal.\n" +
"If you omit all arguments a GUI is started instead.";

private boolean graphicalInterfaceRequested;
private boolean printHelpMessage;
private Mode mode;
private int key;
private String[] args;

public void processArguments(String[] args) {
this.args = args.clone();

if (args.length == 0) {
graphicalInterfaceRequested = true;
return;
}

if (args.length = 2 &&
(args[1].startsWith("0x") || args[1].startsWith("0X"))) {
String keyString = args[1].substring(2).trim().toLowerCase();

try {
key = Integer.parseInt(keyString, 16);
} catch (NumberFormatException ex) {
printHelpMessage = true;
return;
}
} else {
try {
key =

Specifying a key

From a UX perspective, I think it will help if you can also indicate that the key should either be prefixed with 0x, so that you will treat it as a hexadecimal value, or it should be an integer.

Code duplication

And speaking about parsing the input keys, there's some code duplication in App.processArguments(String[]) and MyActionListener.actionPerformed(ActionEvent). You should consider refactoring the integer parsing part out so that it can be shared in both places.

Getting a file list

private List getFileList(String[] args) {
    // We subtract 2 in order to omit the fist two arguments in 'args' that
    // are the switch and the key.
    List fileList = new ArrayList<>(args.length - 2);

    for (int i = 2; i < args.length; ++i) {
        fileList.add(new File(args[i]));
    }

    return fileList;
}

I think it'll be better if a processed args array without the initial command-line arguments is passed in here. Anyways, assuming if you prefer to keep to the current approach, you can use the familiar stream processing for this too:

private List getFileList(String[] args) {
    return Arrays.stream(args)
                    .skip(2)
                    .map(File::new)
                    .collect(Collectors.toList());
}

In fact, this will make refactoring easier when args no longer have the additional arguments: you can just remove the line .skip(2).

StackExchange Code Review Q#121657, answer score: 4