java GUI创建的线程安全问题

时间:2010-12-26 17:17:47

标签: java swing

在以下sample code中,

/*
 * Copyright (c) 1995, 2008, Oracle and/or its affiliates. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Oracle or the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */ 

package components;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

/* TopLevelDemo.java requires no other files. */
public class TopLevelDemo {
    /**
     * Create the GUI and show it.  For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {
        //Create and set up the window.
        JFrame frame = new JFrame("TopLevelDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //Create the menu bar.  Make it have a green background.
        JMenuBar greenMenuBar = new JMenuBar();
        greenMenuBar.setOpaque(true);
        greenMenuBar.setBackground(new Color(154, 165, 127));
        greenMenuBar.setPreferredSize(new Dimension(200, 20));

        //Create a yellow label to put in the content pane.
        JLabel yellowLabel = new JLabel();
        yellowLabel.setOpaque(true);
        yellowLabel.setBackground(new Color(248, 213, 131));
        yellowLabel.setPreferredSize(new Dimension(200, 180));

        //Set the menu bar and add the label to the content pane.
        frame.setJMenuBar(greenMenuBar);
        frame.getContentPane().add(yellowLabel, BorderLayout.CENTER);

        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
}

函数createAndShowGUI()上面的注释,“为了线程安全,应该从事件派发线程调用此方法。”

你能解释为什么应该从事件派发线程调用这个方法。我试图把这个方法放在public void main方法中,但没关系。

1 个答案:

答案 0 :(得分:5)

它可能适合您,但这并不意味着它可以在任何地方使用。 (几乎)所有对Swing类的访问都应该从EDT执行,如Javadocs中所述。这包括初始创建JFrame和组件:

  

一般来说,Swing不是线程安全的。除非另有说明,否则必须在事件派发线程上访问所有Swing组件和相关类。

     

...

     

然而,影响在于构建和显示Swing应用程序。不会在事件派发线程上调用对应用程序的主方法或Applet中的方法的调用。因此,在构造和显示应用程序或小程序时,必须注意将控制权转移到事件派发线程。

过去,这种“初始创建”规则并不存在,但在使用此方法时会发现一些线程问题。如果我找到相关的讨论,我会在这里链接。

更新:我发现this answer on Stack Overflow讨论了Swing单线程策略规则及其更改,以禁止从其他线程访问“尚未实现”的组件。