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            <div id=PageTitle>How to Use Password Fields</div>
            <blockquote>
The
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JPasswordField.html"><code>JPasswordField</code></a> class, a subclass of <code>JTextField</code>,
provides text fields specialized for password entry.
For security reasons,
a password field doesn't show the characters the user types.
Instead, the field displays another character
such as an asterisk '*'.
As another security precaution,
a password field stores its value
as an array of characters,
rather than as a string.
Like an ordinary <a href="textfield.html">text field</a>,
a password field fires an
<a class="TutorialLink" target="_top" href="../events/actionlistener.html">action event</a> when the user indicates that text entry is complete,
such as by pressing the Enter button.

<p>
Here's a picture of a demo
that brings up a small window
and prompts the user to type in a password.

<p><center><IMG SRC="../../figures/uiswing/components/PasswordDemo.png" WIDTH="325" HEIGHT="96" ALIGN="BOTTOM" ALT="A snapshot of PasswordDemo, which uses a password field"></center></p>
<p>
You can
<a href="http://java.sun.com/docs/books/tutorialJWS/uiswing/components/examples/PasswordDemo.jnlp">run PasswordDemo</a> (it requires release 6) using
<a class="TutorialLink" target="_top" href="../../information/javawebstart.html">Java<sup><font size=-2>TM</font></sup> Web Start</a>.
(The password is "bugaboo".)
The source code is in
<a class="SourceLink" target="_blank" href="examples/PasswordDemo.java"><code><code>PasswordDemo.java</code></code></a>.
Here's the code that creates
and sets up the password field:

<blockquote><pre>
passwordField = new JPasswordField(10);
passwordField.setActionCommand(OK);
passwordField.addActionListener(this);
</pre></blockquote>

The argument passed into the <code>JPasswordField</code> constructor
indicates the preferred size of the field &#151;
at least 10 columns wide, in this case.
By default a password field displays a dot for
each character typed. Calling <code>setEchoChar</code>
allows it to be changed to another character.
Finally, the code adds an action listener to the password field,
which checks the value typed in by the user.
Here's the implementation of the action listener's
<code>actionPerformed</code> method:

<blockquote><pre>
public void actionPerformed(ActionEvent e) {
    String cmd = e.getActionCommand();

    if (OK.equals(cmd)) { //Process the password.
        <b>char[] input = passwordField.getPassword();</b>
        if (isPasswordCorrect(input)) {
            JOptionPane.showMessageDialog(controllingFrame,
                "Success! You typed the right password.");
        } else {
            JOptionPane.showMessageDialog(controllingFrame,
                "Invalid password. Try again.",
                "Error Message",
                JOptionPane.ERROR_MESSAGE);
        }

        //Zero out the possible password, for security.
        for (int i = 0; i < input.length; i++) {
            input[i] = 0;
        }

        passwordField.selectAll();
        resetFocus();
    } else <em>...//handle the Help button...</em>
}
</pre></blockquote>

<blockquote><hr><strong>Security note:</strong>&nbsp;Although the <code>JPasswordField</code> class
inherits the <code>getText</code> method,
you should use the <code>getPassword</code> method instead.
Not only is <code>getText</code> less secure,
but in the future it might return the visible string
(for example, <code>"******"</code>)
instead of the typed-in string.

<p>
To further enhance security,
once you are finished with the character array returned by
<code>getPassword</code>,
you should set each of its elements to zero.
The preceding code snippet shows how to do this.
<hr></blockquote>

<p>
A program using a password field typically
validates the password before completing any actions
requiring the password.
This program calls a private method,
<code>isPasswordCorrect</code>,
that compares the value returned by <code>getPassword</code>
to a value stored in a character array.
Here is its code:

<blockquote><pre>
private static boolean isPasswordCorrect(char[] input) {
    boolean isCorrect = true;
    char[] correctPassword = { 'b', 'u', 'g', 'a', 'b', 'o', 'o' };

    if (input.length != correctPassword.length) {
        isCorrect = false;
    } else {
        for (int i = 0; i < input.length; i++) {
            if (input[i] != correctPassword[i]) {
                isCorrect = false;
            }
        }
    }

    //Zero out the password.
    for (int i = 0; i < correctPassword.length; i++) {
        correctPassword[i] = 0;
    }

    return isCorrect;
}
</pre></blockquote>


</blockquote>
<h3>
<a name="api">The Password Field API</a>
</h3>
<blockquote>
The following tables list the commonly used
<code>JPasswordField</code>
constructors and methods.
For information on the API
password fields inherit,
see
<a href="textfield.html">How to Use Text Fields</a>.


<p>

<table border=1>
<caption><a name="JPasswordFieldapi">Commonly Used JPasswordField Constructors
and Methods</a></caption>
<tr>
<th>Constructor or Method
</th>
<th>Purpose

</th>
</tr>
  <tr>
    <td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JPasswordField.html#JPasswordField()">JPasswordField()</a>    <br>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JPasswordField.html#JPasswordField(java.lang.String)">JPasswordField(String)</a>    <br>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JPasswordField.html#JPasswordField(java.lang.String, int)">JPasswordField(String, int)</a>    <br>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JPasswordField.html#JPasswordField(int)">JPasswordField(int)</a>    <br>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JPasswordField.html#JPasswordField(javax.swing.text.Document, java.lang.String, int)">JPasswordField(Document, String, int)</a>
  </td>
    <td>Create a password field.
        When present, the <code>int</code> argument specifies the desired width
        in columns.
        The <code>String</code> argument contains the field's initial text.
        The <code>Document</code> argument provides a custom model for
        the field.

    </td>
  </tr>
  <tr>
    <td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JPasswordField.html#getPassword()">char[] getPassword()</a>    </td>
    <td>Set or get the text displayed by the password field.
    </td>
  </tr>
  <tr>
    <td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JPasswordField.html#setEchoChar(char)">void setEchoChar(char)</a>    <br>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JPasswordField.html#getEchoChar()">char getEchoChar()</a>    </td>
    <td>Set or get the echo character &#151; the character displayed
        instead of the actual characters typed by the user.

    </td>
  </tr>
  <tr>
    <td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JTextField.html#addActionListener(java.awt.event.ActionListener)">void addActionListener(ActionListener)</a>    <br>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JTextField.html#removeActionListener(java.awt.event.ActionListener)">void removeActionListener(ActionListener)</a>    <br>
<em>(defined in <code>JTextField</code>)</em>
    </td>
    <td>Add or remove an action listener.
    </td>
  </tr>

  <tr>
    <td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/text/JTextComponent.html#selectAll()">void selectAll()</a><br>
<em>(defined in <code>JTextComponent</code>)</em>
    </td>
    <td>Select all characters in the password field.
    </td>
  </tr>
</table>
</blockquote>

<h3>
<a name="eg">Examples that Use Password Fields</a>
</h3>
<blockquote>
<a href="examples/index.html#PasswordDemo">PasswordDemo</a>
is the Tutorial's only example that uses
a <code>JPasswordField</code> object.
However, the Tutorial has many examples that use
<code>JTextField</code>s,
whose API is inherited by <code>JPasswordField</code>.
See <a href="textfield.html#eg">Examples that Use Text Fields</a>
for further information.

        </blockquote>
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