UnixPasswordField -- A unix style password input

UnixPasswordField.java

/*
 * UnixPasswordField -- A unix style password input
 * Copyright (C) 2012  Jakob Schöttl
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package kj.scotlyard.board;

import java.awt.event.KeyEvent;

import javax.swing.JPasswordField;
import javax.swing.UIManager;

/**
 * This class implements a unix style password input. Similar like this:
 * <p>
 * <tt>read -s -p "Password: " VARIABLE</tt>
 * </p>
 * <tt>-s</tt> silent, no echo; <tt>-p</tt> prompt text, not implemented here of
 * course; into <tt>VARIABLE</tt>, can be retrieved by
 * <code>getPassword()</code>. Neither copy, cut nor paste are supported.
 * 
 * Note that there is <i>no</i> protection mechanism against spy progs which
 * look into the program memory.
 * 
 * @author Jakob Schöttl
 * 
 */
@SuppressWarnings("serial")
public class UnixPasswordField extends JPasswordField {
	
	private StringBuffer password = new StringBuffer();
	
	public UnixPasswordField() { }

	public UnixPasswordField(int columns) {
		super(columns);
	}
	
	private void provideErrorFeedback() {
		UIManager.getLookAndFeel().provideErrorFeedback(this);
	}

	@Override
	public char getEchoChar() {
		return 0;
	}

	/**
	 * Not supported; This method will do NOTHING. The echo character is not
	 * changeable and will always be <tt>0</tt> (on the surface), that is
	 * <i>no</i> echo character is displayed.
	 */
	@Override
	public void setEchoChar(char c) { }

	@Override
	public char[] getPassword() {
		final int l = password.length();
		char[] result = new char[l];
		password.getChars(0, l, result, 0);
		return result;
	}

	@Override
	protected void processKeyEvent(KeyEvent e) {
		if (e.getID() == KeyEvent.KEY_TYPED) {
			char c = e.getKeyChar();
			switch (c) {
			case KeyEvent.VK_BACK_SPACE:
				int l = password.length();
				if (l > 0) {
					password.deleteCharAt(l - 1);
				} else {
					// Ein UnixPasswordField soll NICHTS ueber das Passwort verraten
					// Also soll man auch nicht nach Passworteingabe, die Anzahl der
					// eingegebenen Zeichen zaehlen koennen.
					// Ansonsten waere folgendes aber ganz nett:
//					provideErrorFeedback();
				}
				break;
	
			default:
				password.append(c);
				break;
			}
		} else {
			super.processKeyEvent(e);
		}
	}

	@Override
	public void cut() {
		provideErrorFeedback();
	}

	@Override
	public void copy() {
		provideErrorFeedback();
	}

	@Override
	public void paste() {
		provideErrorFeedback();
	}
	
	@Override
	public void setText(String s) {
		password.setLength(0);
		password.append(s);
	}
	
	/**
	 * Clear the password (like <code>setText("")</code>
	 * for normal text fields).
	 */
	public void clear() {
		password.setLength(0);
	}
	
	/**
	 * Check weather the password is blank.
	 * @return <code>true</code> if the password is empty
	 */
	public boolean isPasswordEmpty() {
		return password.length() == 0;
	}

}

Automatisch clear() on FOCUS_GAINED ist doch keine gute Idee.
Entweder auskommentieren, dass der Anwender am Ende entscheiden kann, oder so etwas wie setClearOnFocusGained(boolean), default false.

Vielleicht zusaetzlich etwas wie setFeedbackWhenEmpty(boolean), default false. Zum ein-/ausschalten des "ErrorFeedback" bei Backspace und leerem Passwort.

Zum Abfragen ob Passwort eingegeben wurde bzw. ob es leer ist:

boolean isPasswordEmpty() {
    return password.length() == 0;
}

Empty oder Blank? Empty kommt in Java schon haeufiger vor ...

Bugfix: setText musste noch überschrieben werden: Damit wird, wie bei JPasswordField, das Passwort gesetzt. Allerdings dürfen beim UnixPasswordField keine echoChars im Textfeld erscheinen!