src/java.desktop/share/classes/javax/swing/JButton.java

/*
 * Copyright (c) 1997, 2021, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package javax.swing;

import java.beans.BeanProperty;
import java.beans.ConstructorProperties;
import java.beans.JavaBean;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.io.Serial;

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

/**
 * An implementation of a "push" button.
  * <p>
 * Buttons can be configured, and to some degree controlled, by
 * <code><a href="Action.html">Action</a></code>s.  Using an
 * <code>Action</code> with a button has many benefits beyond directly
 * configuring a button.  Refer to <a href="Action.html#buttonActions">
 * Swing Components Supporting <code>Action</code></a> for more
 * details, and you can find more information in <a
 * href="https://docs.oracle.com/javase/tutorial/uiswing/misc/action.html">How
 * to Use Actions</a>, a section in <em>The Java Tutorial</em>.
 * <p>
 * See <a href="https://docs.oracle.com/javase/tutorial/uiswing/components/button.html">How to Use Buttons, Check Boxes, and Radio Buttons</a>
 * in <em>The Java Tutorial</em>
 * for information and examples of using buttons.
 * <p>
 * <strong>Warning:</strong> Swing is not thread safe. For more
 * information see <a
 * href="package-summary.html#threading">Swing's Threading
 * Policy</a>.
 * <p>
 * <strong>Warning:</strong>
 * Serialized objects of this class will not be compatible with
 * future Swing releases. The current serialization support is
 * appropriate for short term storage or RMI between applications running
 * the same version of Swing.  As of 1.4, support for long term storage
 * of all JavaBeans
 * has been added to the <code>java.beans</code> package.
 * Please see {@link java.beans.XMLEncoder}.
 *
 * @author Jeff Dinkins
 * @since 1.2
 */
@JavaBean(defaultProperty = "UIClassID", description = "An implementation of a \"push\" button.")
@SwingContainer(false)
@SuppressWarnings("serial")
public class JButton extends AbstractButton implements Accessible {

    /**
     * @see #getUIClassID
     * @see #readObject
     */
    private static final String uiClassID = "ButtonUI";

    /**
     * Creates a button with no set text or icon.
     */
    public JButton() {
        this(null, null);
    }

    /**
     * Creates a button with an icon.
     *
     * @param icon  the Icon image to display on the button
     */
    public JButton(Icon icon) {
        this(null, icon);
    }

    /**
     * Creates a button with text.
     *
     * @param text  the text of the button
     */
    @ConstructorProperties({"text"})
    public JButton(String text) {
        this(text, null);
    }

    /**
     * Creates a button where properties are taken from the
     * <code>Action</code> supplied.
     *
     * @param a the <code>Action</code> used to specify the new button
     *
     * @since 1.3
     */
    public JButton(Action a) {
        this();
        setAction(a);
    }

    /**
     * Creates a button with initial text and an icon.
     *
     * @param text  the text of the button
     * @param icon  the Icon image to display on the button
     */
    public JButton(String text, Icon icon) {
        // Create the model
        setModel(new DefaultButtonModel());

        // initialize
        init(text, icon);
    }

    /**
     * Resets the UI property to a value from the current look and
     * feel.
     *
     * @see JComponent#updateUI
     */
    public void updateUI() {
        setUI((ButtonUI)UIManager.getUI(this));
    }


    /**
     * Returns a string that specifies the name of the L&amp;F class
     * that renders this component.
     *
     * @return the string "ButtonUI"
     * @see JComponent#getUIClassID
     * @see UIDefaults#getUI
     */
    @BeanProperty(bound = false, expert = true, description
            = "A string that specifies the name of the L&F class.")
    public String getUIClassID() {
        return uiClassID;
    }


    /**
     * Gets the value of the <code>defaultButton</code> property,
     * which if <code>true</code> means that this button is the current
     * default button for its <code>JRootPane</code>.
     * Most look and feels render the default button
     * differently, and may potentially provide bindings
     * to access the default button.
     *
     * @return the value of the <code>defaultButton</code> property
     * @see JRootPane#setDefaultButton
     * @see #isDefaultCapable
     */
    @BeanProperty(bound = false, description
            = "Whether or not this button is the default button")
    public boolean isDefaultButton() {
        JRootPane root = SwingUtilities.getRootPane(this);
        if (root != null) {
            return root.getDefaultButton() == this;
        }
        return false;
    }

    /**
     * Gets the value of the <code>defaultCapable</code> property.
     *
     * @return the value of the <code>defaultCapable</code> property
     * @see #setDefaultCapable
     * @see #isDefaultButton
     * @see JRootPane#setDefaultButton
     */
    public boolean isDefaultCapable() {
        return defaultCapable;
    }

    /**
     * Sets the <code>defaultCapable</code> property,
     * which determines whether this button can be
     * made the default button for its root pane.
     * The default value of the <code>defaultCapable</code>
     * property is <code>true</code> unless otherwise
     * specified by the look and feel.
     *
     * @param defaultCapable <code>true</code> if this button will be
     *        capable of being the default button on the
     *        <code>RootPane</code>; otherwise <code>false</code>
     * @see #isDefaultCapable
     */
    @BeanProperty(visualUpdate = true, description
            = "Whether or not this button can be the default button")
    public void setDefaultCapable(boolean defaultCapable) {
        boolean oldDefaultCapable = this.defaultCapable;
        this.defaultCapable = defaultCapable;
        firePropertyChange("defaultCapable", oldDefaultCapable, defaultCapable);
    }

    /**
     * Overrides <code>JComponent.removeNotify</code> to check if
     * this button is currently set as the default button on the
     * <code>RootPane</code>, and if so, sets the <code>RootPane</code>'s
     * default button to <code>null</code> to ensure the
     * <code>RootPane</code> 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();
    }

    /**
     * See readObject() and writeObject() in JComponent for more
     * information about serialization in Swing.
     */
    @Serial
    private void writeObject(ObjectOutputStream s) throws IOException {
        s.defaultWriteObject();
        if (getUIClassID().equals(uiClassID)) {
            byte count = JComponent.getWriteObjCounter(this);
            JComponent.setWriteObjCounter(this, --count);
            if (count == 0 && ui != null) {
                ui.installUI(this);
            }
        }
    }


    /**
     * Returns a string representation of this <code>JButton</code>.
     * This method is intended to be used only for debugging purposes, and the
     * content and format of the returned string may vary between
     * implementations. The returned string may be empty but may not
     * be <code>null</code>.
     *
     * @return  a string representation of this <code>JButton</code>
     */
    protected String paramString() {
        String defaultCapableString = (defaultCapable ? "true" : "false");

        return super.paramString() +
            ",defaultCapable=" + defaultCapableString;
    }


/////////////////
// Accessibility support
////////////////

    /**
     * Gets the <code>AccessibleContext</code> associated with this
     * <code>JButton</code>. For <code>JButton</code>s,
     * the <code>AccessibleContext</code> takes the form of an
     * <code>AccessibleJButton</code>.
     * A new <code>AccessibleJButton</code> instance is created if necessary.
     *
     * @return an <code>AccessibleJButton</code> that serves as the
     *         <code>AccessibleContext</code> of this <code>JButton</code>
     */
    @BeanProperty(bound = false, expert = true, description
            = "The AccessibleContext associated with this Button.")
    public AccessibleContext getAccessibleContext() {
        if (accessibleContext == null) {
            accessibleContext = new AccessibleJButton();
        }
        return accessibleContext;
    }

    /**
     * This class implements accessibility support for the
     * <code>JButton</code> class.  It provides an implementation of the
     * Java Accessibility API appropriate to button user-interface
     * elements.
     * <p>
     * <strong>Warning:</strong>
     * Serialized objects of this class will not be compatible with
     * future Swing releases. The current serialization support is
     * appropriate for short term storage or RMI between applications running
     * the same version of Swing.  As of 1.4, support for long term storage
     * of all JavaBeans
     * has been added to the <code>java.beans</code> package.
     * Please see {@link java.beans.XMLEncoder}.
     */
    @SuppressWarnings("serial")
    protected class AccessibleJButton extends AccessibleAbstractButton {

        /**
         * Constructs an {@code AccessibleJButton}.
         */
        protected AccessibleJButton() {}

        /**
         * Get the role of this object.
         *
         * @return an instance of AccessibleRole describing the role of the
         * object
         * @see AccessibleRole
         */
        public AccessibleRole getAccessibleRole() {
            return AccessibleRole.PUSH_BUTTON;
        }
    } // inner class AccessibleJButton
}