InputVerifier.java

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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * 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);
  }

}