Swing Thread安全编程

Question

public static void main(String args[]) {
    /* Set the Nimbus look and feel */
    //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
    /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
     * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
     */
    try {
        for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
            if ("Nimbus".equals(info.getName())) {
                javax.swing.UIManager.setLookAndFeel(info.getClassName());
                break;
            }
        }
    } catch (ClassNotFoundException ex) {
        java.util.logging.Logger.getLogger(MyDialog.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(MyDialog.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(MyDialog.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(MyDialog.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }
    //</editor-fold>

    /* Create and display the dialog */
    java.awt.EventQueue.invokeLater(new Runnable() {
        public void run() {
            MyDialog dialog = new MyDialog(new javax.swing.JFrame(), true);
            dialog.addWindowListener(new java.awt.event.WindowAdapter() {
                @Override
                public void windowClosing(java.awt.event.WindowEvent e) {
                    System.exit(0);
                }
            });
            dialog.setVisible(true);
        }
    });
}

MyDialog类只有很少的组合和文本字段,并且正在使用DB值填充组合.在选择一个组合值时,我从DB获取另一个值以填充下一个组合.

上述程序在不使用invokeLater线程的情况下以相同的方式运行.什么时候invokeLater在Swing编程中变得有用.我已经阅读了一些关于它的内容,但似乎都是理论上的.invokeLater对应用程序有何不同？仅仅在main方法中使用它还是应该在动作监听器中使用它是否足够？

SwingUtilities.invokeLater和java.awt.EventQueue.invokeLater - 它们是一样的吗？

Answer 1

没有什么理论上的.这很实用.该SwingUtilities.invokeLater()方法保证了将在其中Runnable运行的代码Event Dispatch Thread (EDT).这很重要,因为Swing不是线程安全的,因此任何与GUI(Swing等)相关的东西都需要运行EDT.这EDT是一个"只要它发生就会发生"的线程,它不能保证执行事务的顺序.如果GUI代码在后台线程中执行(例如,在SwingWorker实例中),那么它可能会抛出错误.我学到了很多困难:在我学习的几年里,在后台线程中执行GUI更改代码导致RuntimeException了我无法理解的随机,不一致的问题.这是一个很好的学习经历(SwingWorker有一个doInBackground()后台任务的done()方法和EDT任务的方法).

以同样的方式,您不希望在后台线程上执行GUI代码,您也不希望在上面执行大型操作(数据库查询等)EDT.这是因为它EDT正在调度所有GUI事件,因此所有内容都EDT应该非常简短和甜蜜.你可以通过一JProgressBar组不确定来轻松看到这一点.

这个SSCCE应该很好地说明它.注意JProgressBaras 的动作method(),一次在后台线程上,一次在EDT线程上.

import javax.swing.JFrame;
import javax.swing.JProgressBar;
import javax.swing.SwingWorker;

/**
 *
 * @author Ryan
 */
public class Test {

    public static void main(String args[]) {
        JFrame frame = new JFrame();
        JProgressBar jpb = new JProgressBar();
        jpb.setIndeterminate(true);
        frame.add(jpb);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        new Task().execute();
    }

    public static void method() { // This is a method that does a time-consuming task.
        for(int i = 1; i <= 5; i++) {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(i);
        }
    }

    static class Task extends SwingWorker<Void, Void> {

        @Override
        protected Void doInBackground() throws Exception {
            /* Executing method on background thread.
             * The loading bar should keep moving because, although method() is time consuming, we are on a background thread.
            */ 
            method();
            return null;
        }

        @Override
        protected void done() {
            /* Executing method on Event Dispatch Thread.
             * The loading bar should stop because method() is time consuming and everything on the Event Dispatch Thread
             * (like the motion of the progress bar) is waiting for it to finish.
            */

            // 
            method();
        }
    }
}

希望这可以帮助.