JButton.java

/* JButton.java --
   Copyright (C) 2002, 2004, 2005, 2006, Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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General Public License for more details.

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02110-1301 USA.

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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
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package javax.swing;

import javax.accessibility.Accessible;
import javax.accessibility.AccessibleContext;
import javax.accessibility.AccessibleRole;
import javax.swing.plaf.ButtonUI;


/**
 * A general purpose push button. <code>JButton</code>s can display a label,
 * an {@link Icon} or both.
 *
 * @author Ronald Veldema (rveldema@cs.vu.nl)
 */
public class JButton extends AbstractButton
  implements Accessible
{

  /**
   * Accessibility support for JButtons.
   */
  protected class AccessibleJButton
    extends AbstractButton.AccessibleAbstractButton
  {
    /**
     * Returns the accessible role that this component represents.
     * This is {@link AccessibleRole#PUSH_BUTTON} for <code>JButton</code>s.
     *
     * @return the accessible role that this component represents
     */
    public AccessibleRole getAccessibleRole()
    {
      return AccessibleRole.PUSH_BUTTON;
    }
  }

  private static final long serialVersionUID = -1907255238954382202L;

  /**
   * Indicates if this button is capable to become the default button.
   */
  private boolean defaultCapable;

  /**
   * Creates a new button with an empty string for the button text and no
   * icon.
   */
  public JButton()
  {
    this(null, null);
  }

  /**
   * Creates a new button from the specified action.
   * 
   * @param a  the action (<code>null</code> permitted).
   * 
   * @see AbstractButton#setAction(Action)
   */
  public JButton(Action a)
  {
    this();
    setAction(a);
  }

  /**
   * Creates a new button with the specified icon (and an empty string for
   * the button text).
   * 
   * @param icon  the icon (<code>null</code> permitted).
   */
  public JButton(Icon icon)
  {
    this(null, icon);
  }

  /**
   * Creates a new button with the specified text and no icon.
   * 
   * @param text  the button text (<code>null</code> permitted, will be
   *     substituted by an empty string).
   */
  public JButton(String text)
  {
    this(text, null);
  }

  /**
   * Creates a new button with the specified text and icon.
   * 
   * @param text  the button text (<code>null</code> permitted, will be
   *     substituted by an empty string).
   * @param icon  the icon (<code>null</code> permitted).
   */
  public JButton(String text, Icon icon)
  {
    super();
    setModel(new DefaultButtonModel());
    init(text, icon);
    defaultCapable = true;
  }

  protected void configurePropertiesFromAction(Action a)
  { 
    super.configurePropertiesFromAction(a);
  }

  /**
   * Returns the object that provides accessibility features for this
   * <code>JButton</code> component.
   *
   * @return The accessible context (an instance of {@link AccessibleJButton}).
   */
  public AccessibleContext getAccessibleContext()
  {
    if (accessibleContext == null)
      accessibleContext = new AccessibleJButton();
    return accessibleContext;
  }

  /**
   * Returns the suffix (<code>"ButtonUI"</code> in this case) used to 
   * determine the class name for a UI delegate that can provide the look and 
   * feel for a <code>JButton</code>.
   *
   * @return <code>"ButtonUI"</code>.
   */
  public String getUIClassID()
  {
    // Returns a string that specifies the name of the L&F class that renders
    // this component.  
    return "ButtonUI";
  }

  /**
   * Returns <code>true</code> if this button is the default button in
   * its <code>JRootPane</code>. The default button gets automatically
   * activated when the user presses <code>ENTER</code> (or whatever
   * key this is bound to in the current Look and Feel).
   *
   * @return <code>true</code> if this button is the default button in
   *         its <code>JRootPane</code>
   *
   * @see #isDefaultCapable()
   * @see #setDefaultCapable(boolean)
   * @see JRootPane#getDefaultButton()
   * @see JRootPane#setDefaultButton(JButton)
   */
  public boolean isDefaultButton()
  {
    // The default button is managed by the JRootPane, so the safest way
    // to determine this property is to ask the root pane of this button,
    // if it exists.
    JRootPane rp = SwingUtilities.getRootPane(this);
    boolean isDefault = false;
    if (rp != null)
      isDefault = rp.getDefaultButton() == this;
    return isDefault;
  }

  /**
   * Returns <code>true</code> if this button can act as the default button.
   * This is <code>true</code> by default.
   *
   * @return <code>true</code> if this button can act as the default button
   *
   * @see #setDefaultCapable(boolean)
   * @see #isDefaultButton()
   * @see JRootPane#getDefaultButton()
   * @see JRootPane#setDefaultButton(JButton)
   */
  public boolean isDefaultCapable()
  {
    // Returns whether or not this button is capable of being the default
    // button on the RootPane. 
    return defaultCapable;
  }

  /**
   * Returns an implementation-dependent string describing the attributes of
   * this <code>JButton</code>.
   *
   * @return A string describing the attributes of this <code>JButton</code>
   *         (never <code>null</code>).
   */
  protected String paramString()
  {
    String superParam = super.paramString();

    // 41 is the maximum number of chars which may be needed.
    StringBuffer sb = new StringBuffer(41);
    sb.append(",defaultButton=").append(isDefaultButton());
    sb.append(",defaultCapable=").append(defaultCapable);

    return superParam + sb.toString();
  }

  /**
   * Overrides JComponent.removeNotify to check if this button is currently
   * set as the default button on the RootPane, and if so, sets the RootPane's
   * default button to null to ensure the RootPane doesn't hold onto an invalid
   * button reference.
   */
  public void removeNotify()
  {
    JRootPane root = SwingUtilities.getRootPane(this);
    if (root != null && root.getDefaultButton() == this)
      root.setDefaultButton(null);
    super.removeNotify();
  }

  /**
   * Sets the <code>defaultCapable</code> property which indicates if
   * this button may become the default button in its <code>JRootPane</code>.
   *
   * @param defaultCapable <code>true</code> if this button can become the
   *        default button in its JRootPane, <code>false</code> otherwise
   *
   * @see #setDefaultCapable(boolean)
   * @see #isDefaultButton()
   * @see JRootPane#getDefaultButton()
   * @see JRootPane#setDefaultButton(JButton)
   */
  public void setDefaultCapable(boolean defaultCapable)
  {
    this.defaultCapable = defaultCapable;
  }

  /**
   * Sets this button's UI delegate to the default (obtained from the
   * {@link UIManager}) for the current look and feel.
   */
  public void updateUI()
  {
    setUI((ButtonUI) UIManager.getUI(this));
  }
}