Question

Unix / Linux support auto-complete of files and directories when pressing “tab”.
I need to create this ability in my windows application. I have a text field for user input of file name, which I want to respond to a “tab” press like it will do when we’re in a unix console:

1. If there is one option – Auto-complete.
2. Some options – show a list of the options.
3. No options – nada.

For my SSH connection to my unix machine I use the ch.ethz.ssh API.

Is there a way to do so?

Answer 1

First you want to have a text field without focus cycling, and tab suppression:

jTextField1.setFocusCycleRoot(true);
jTextField1.setFocusTraversalKeysEnabled(false);       

Then a data model for the files (here local directory, but SSH is likewise):

private File dir = new File("C:/Work");
private String typedPrefix = null;
private List<String> filesWithPrefix = new ArrayList<>();

Then a key pressed handling for the TAB:

• Consume the event.
• Get the prefix upto the caret for searching file names.
• If you merely need to restrict already found file names, so do, otherwise physical search them.

• Look for the longest common prefix in the file names. Display that.

  private void jTextField1KeyPressed(java.awt.event.KeyEvent evt) {
  System.out.println("KeyPressed " + evt);
  
  if (evt.getKeyCode() == KeyEvent.VK_TAB) {
      evt.consume();
  
      int caretPos = jTextField1.getCaretPosition();
      try {
          final String newPrefix = jTextField1.getText(0, caretPos);
          System.out.println("newPrefix: " + newPrefix);
          if (!newPrefix.isEmpty()) {
              if (typedPrefix == null || !newPrefix.startsWith(typedPrefix)) {
                  // Must physically reload possible values:
                  String[] fileNames = dir.list(new FilenameFilter() {
  
                      @Override
                      public boolean accept(File dir, String name) {
                          return name.startsWith(newPrefix);
                      }
                  });
                  filesWithPrefix.clear();
                  Collections.addAll(filesWithPrefix, fileNames);
                  typedPrefix = newPrefix;
              } else {
                  // Can reduce prior selection:
                  for (ListIterator<String> it = filesWithPrefix.listIterator(); it.hasNext(); ) {
                      String fileName = it.next();
                      if (!fileName.startsWith(newPrefix)) {
                          it.remove();
                      }
                  }
                  typedPrefix = newPrefix;
              }
              System.out.println("filesWithPrefix: " +filesWithPrefix);
              if (!filesWithPrefix.isEmpty()) {
                  // Find longest common prefix:
                  String longestCommonPrefix = null;
                  for (String fileName : filesWithPrefix) {
                      if (longestCommonPrefix == null) {
                          longestCommonPrefix = fileName;
                      } else {
                          while (!fileName.startsWith(longestCommonPrefix)) {
                              longestCommonPrefix = longestCommonPrefix.substring(0, longestCommonPrefix.length() - 1);
                          }
                      }
                  }
                  if (longestCommonPrefix.length() > typedPrefix.length()) {
                      jTextField1.setText(longestCommonPrefix);
                      jTextField1.setCaretPosition(longestCommonPrefix.length());
                      typedPrefix = longestCommonPrefix;
                  }
                  if (filesWithPrefix.size() > 1) {
                      // Show popup:
                      ;;;
                  } else if (filesWithPrefix.size() == 1) {
                      // File selected:
                      System.beep();
                  }
              }
          }
      } catch (BadLocationException ex) {
          Logger.getLogger(TabsJFrame.class.getName()).log(Level.SEVERE, null, ex);
      }
  }
  }
  

What is missing is the display of the ambiguous file names. Popup menu would be nice, wouldn’t it?

Popup:

                    // Show popup:
                    JPopupMenu popup = new JPopupMenu();
                    for (String fileName : filesWithPrefix) {
                        popup.add(new AbstractAction(fileName) {
                             @Override
                            public void actionPerformed(ActionEvent e) {
                                jTextField1.setText(e.getActionCommand());
                            }
                        });
                    }
                    Point pt = jTextField1.getCaret().getMagicCaretPosition();
                    popup.show(jTextField1, pt.x, pt.y + 5);