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 * published by the Free Software Foundation.  Oracle designates this

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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

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 * accompanied this code).

 *

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package javax.swing;

import java.util.*;

/**

 * The purpose of this class is to help clients support smooth focus

 * navigation through GUIs with text fields. Such GUIs often need

 * to ensure that the text entered by the user is valid (for example,

 * that it's in

 * the proper format) before allowing the user to navigate out of

 * the text field. To do this, clients create a subclass of

 * <code>InputVerifier</code> and, using <code>JComponent</code>'s

 * <code>setInputVerifier</code> method,

 * attach an instance of their subclass to the <code>JComponent</code> whose input they

 * want to validate. Before focus is transfered to another Swing component

 * that requests it, the input verifier's <code>shouldYieldFocus</code> method is

 * called.  Focus is transfered only if that method returns <code>true</code>.

 * <p>

 * The following example has two text fields, with the first one expecting

 * the string "pass" to be entered by the user. If that string is entered in

 * the first text field, then the user can advance to the second text field

 * either by clicking in it or by pressing TAB. However, if another string

 * is entered in the first text field, then the user will be unable to

 * transfer focus to the second text field.

 *

 * <pre>

 * import java.awt.*;

 * import java.util.*;

 * import java.awt.event.*;

 * import javax.swing.*;

 *

 * // This program demonstrates the use of the Swing InputVerifier class.

 * // It creates two text fields; the first of the text fields expects the

 * // string "pass" as input, and will allow focus to advance out of it

 * // only after that string is typed in by the user.

 *

 * public class VerifierTest extends JFrame {

 *     public VerifierTest() {

 *         JTextField tf1 = new JTextField ("Type \"pass\" here");

 *         getContentPane().add (tf1, BorderLayout.NORTH);

 *         tf1.setInputVerifier(new PassVerifier());

 *

 *         JTextField tf2 = new JTextField ("TextField2");

 *         getContentPane().add (tf2, BorderLayout.SOUTH);

 *

 *         WindowListener l = new WindowAdapter() {

 *             public void windowClosing(WindowEvent e) {

 *                 System.exit(0);

 *             }

 *         };

 *         addWindowListener(l);

 *     }

 *

 *     class PassVerifier extends InputVerifier {

 *         public boolean verify(JComponent input) {

 *             JTextField tf = (JTextField) input;

 *             return "pass".equals(tf.getText());

 *         }

 *     }

 *

 *     public static void main(String[] args) {

 *         Frame f = new VerifierTest();

 *         f.pack();

 *         f.setVisible(true);

 *     }

 * }

 * </pre>

 *

 *  @since 1.3

 */

public abstract class InputVerifier {

  /**

   * Checks whether the JComponent's input is valid. This method should

   * have no side effects. It returns a boolean indicating the status

   * of the argument's input.

   *

   * @param input the JComponent to verify

   * @return <code>true</code> when valid, <code>false</code> when invalid

   * @see JComponent#setInputVerifier

   * @see JComponent#getInputVerifier

   *

   */

  public abstract boolean verify(JComponent input);

  /**

   * Calls <code>verify(input)</code> to ensure that the input is valid.

   * This method can have side effects. In particular, this method

   * is called when the user attempts to advance focus out of the

   * argument component into another Swing component in this window.

   * If this method returns <code>true</code>, then the focus is transfered

   * normally; if it returns <code>false</code>, then the focus remains in

   * the argument component.

   *

   * @param input the JComponent to verify

   * @return <code>true</code> when valid, <code>false</code> when invalid

   * @see JComponent#setInputVerifier

   * @see JComponent#getInputVerifier

   *

   */

  public boolean shouldYieldFocus(JComponent input) {

    return verify(input);

  }

}