java - java GUI创建的线程安全问题

Question

如下sample code ,

/*
 * 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，应该从事件调度线程调用此方法。”。

您能否解释一下为什么应该从事件调度线程调用此方法。我尝试过把这个方法放在public void main方法中，但是没有关系。

Answer 1

它可能适合您，但这并不意味着它在任何地方都适用。 (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 JFrame 和组件的初始创建:

In general Swing is not thread safe. All Swing components and related classes, unless otherwise documented, must be accessed on the event dispatching thread.

...

Where the impact lies, however, is in constructing and showing a Swing application. Calls to an application's main method, or methods in Applet, are not invoked on the event dispatching thread. As such, care must be taken to transfer control to the event dispatching thread when constructing and showing an application or applet.

在过去，这种“初始创建”规则是不存在的，但是在使用这种方法时发现了一些线程问题。如果我找到相关讨论，我会将其链接到此处。

更新:我发现this answer on Stack Overflow讨论 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。