我想做什么?
点击Start JButton，SwingWorker就会执行.在 doInBackground() 方法内部，我将 arrNames 的每个索引传递给 publish() 方法，以便在内部显示JTextArea.
At the click of the Start JButton, the SwingWorker will execute. Inside the doInBackground() method, I am passing each index of arrNames, to the publish() method, so that it can be displayed inside the JTextArea.
发生了什么?
如果我不保留行 System.out.format("Counter : %d%n", counter); 作为评论，在我的 SwingWorker 的 doInBackground() 方法中，SwingWorker 正在按预期工作.虽然如果我将其注释掉，那么 SwingWorker 停止响应.
If I do not keep line System.out.format("Counter : %d%n", counter); as a comment, in my doInBackground() method of the SwingWorker, then the SwingWorker is working as expected. Though if I comment it out, then the SwingWorker stops responding.
我做错了吗?
java version "1.7.0_25"
Java(TM) SE Runtime Environment (build 1.7.0_25-b16)
Java HotSpot(TM) Client VM (build 23.25-b01, mixed mode, sharing)
这是我正在使用的代码:
Here is the code I am using :
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class SwingWorkerExample1
{
private JLabel statusLabel;
private JTextArea tArea;
private JButton startButton;
private JButton stopButton;
private BackgroundTask backgroundTask;
private ActionListener buttonActions =
new ActionListener()
{
@Override
public void actionPerformed(ActionEvent ae)
{
JButton source = (JButton) ae.getSource();
if (source == startButton)
{
startButton.setEnabled(false);
stopButton.setEnabled(true);
backgroundTask = new BackgroundTask();
backgroundTask.execute();
}
else if (source == stopButton)
{
backgroundTask.cancel(true);
stopButton.setEnabled(false);
startButton.setEnabled(true);
}
}
};
private void displayGUI()
{
JFrame frame = new JFrame("Swing Worker Example");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
JPanel contentPane = new JPanel();
contentPane.setBorder(
BorderFactory.createEmptyBorder(5, 5, 5, 5));
contentPane.setLayout(new BorderLayout(5, 5));
statusLabel = new JLabel("Status Bar", JLabel.CENTER);
tArea = new JTextArea(20, 20);
tArea.setWrapStyleWord(true);
tArea.setLineWrap(true);
JScrollPane textScroller = new JScrollPane();
textScroller.setBorder(
BorderFactory.createTitledBorder("Textual OUTPUT : "));
textScroller.setViewportView(tArea);
startButton = new JButton("Start");
startButton.addActionListener(buttonActions);
stopButton = new JButton("Stop");
stopButton.setEnabled(false);
stopButton.addActionListener(buttonActions);
JPanel buttonPanel = new JPanel();
buttonPanel.add(startButton);
buttonPanel.add(stopButton);
contentPane.add(statusLabel, BorderLayout.PAGE_START);
contentPane.add(textScroller, BorderLayout.CENTER);
contentPane.add(buttonPanel, BorderLayout.PAGE_END);
frame.setContentPane(contentPane);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
private class BackgroundTask extends SwingWorker<Void, String>
{
private int counter = 0;
private String[] arrNames = { "US Rates Strategy Cash",
"Pavan Wadhwa(1-212) 844-4597", "Srini Ramaswamy(1-212) 844-4983",
"Meera Chandan(1-212) 855-4555", "Kimberly Harano(1-212) 823-4996",
"Feng Deng(1-212) 855-2555", "US Rates Strategy Derivatives",
"Srini Ramaswamy(1-212) 811-4999",
"Alberto Iglesias(1-212) 898-5442",
"Praveen Korapaty(1-212) 812-3444", "Feng Deng(1-212) 812-2456",
"US Rates Strategy Derivatives", "Srini Ramaswamy(1-212) 822-4999",
"Alberto Iglesias(1-212) 822-5098",
"Praveen Korapaty(1-212) 812-3655", "Feng Deng(1-212) 899-2222" };
public BackgroundTask()
{
statusLabel.setText((this.getState()).toString());
System.out.println(this.getState());
}
@Override
protected Void doInBackground()
{
statusLabel.setText((this.getState()).toString());
System.out.println(this.getState());
while (!isCancelled())
{
counter %= arrNames.length;
//System.out.format("Counter : %d%n", counter);
publish(arrNames[counter]);
counter++;
}
statusLabel.setText((this.getState()).toString());
System.out.println(this.getState());
return null;
}
@Override
protected void process(java.util.List<String> messages)
{
for (String message : messages)
tArea.append(String.format(message + "%n"));
}
}
public static void main(String[] args)
{
Runnable runnable = new Runnable()
{
@Override
public void run()
{
new SwingWorkerExample1().displayGUI();
}
};
EventQueue.invokeLater(runnable);
}
}
编辑 1:
按照建议，如果我添加 Thread.sleep(...)，它确实可以工作，但它会抛出一个 InterruptedException，如下所示.所以这个技巧奏效了.但这是合法的执行方式吗?
As suggested, if I add Thread.sleep(...), it does work, though, it throws a InterruptedException as shown below. So the trick works. But is this the legitimate way of performing it ?
C:MineJAVAJ2SEclasses>java SwingWorkerExample1
PENDING
STARTED
java.lang.InterruptedException: sleep interrupted
at java.lang.Thread.sleep(Native Method)
at SwingWorkerExample1$BackgroundTask.doInBackground(SwingWorkerExample1.java:108)
at SwingWorkerExample1$BackgroundTask.doInBackground(SwingWorkerExample1.java:76)
at javax.swing.SwingWorker$1.call(SwingWorker.java:296)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
at java.util.concurrent.FutureTask.run(FutureTask.java:166)
at javax.swing.SwingWorker.run(SwingWorker.java:335)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:724)
DONE
<小时>
只有 doInBackground() 发生了变化，引发了上述异常:
Only doInBackground() is changed, that raised the above exception :
@Override
protected Void doInBackground()
{
Runnable runnable = new Runnable()
{
@Override
public void run()
{
statusLabel.setText((BackgroundTask.this.getState()).toString());
}
};
EventQueue.invokeLater(runnable);
System.out.println(this.getState());
while (!isCancelled())
{
counter %= arrNames.length;
//System.out.format("Counter : %d%n", counter);
publish(arrNames[counter]);
try
{Thread.sleep(30);}
catch(InterruptedException ie)
{ie.printStackTrace();}
counter++;
}
runnable = new Runnable()
{
@Override
public void run()
{
statusLabel.setText((BackgroundTask.this.getState()).toString());
}
};
EventQueue.invokeLater(runnable);
System.out.println(this.getState());
return null;
}
如果我添加 Thread.sleep(...)，它确实有效，但它会抛出一个中断异常
if I add Thread.sleep(...), it does work, though, it throws a InterruptedException
显然产生异常的代码(复制自 OP 的编辑):
The code that apparently produces the exception (copied from OP's edit):
while (!isCancelled()) {
counter %= arrNames.length;
// System.out.format("Counter : %d%n", counter);
publish(arrNames[counter]);
try {
Thread.sleep(30); // throws
} catch (InterruptedException ie) {
ie.printStackTrace();
}
counter++;
}
不过，原因是取消工作人员的代码(在 actionListener 中):
The reason, though, is the code that cancels the worker (in the actionListener):
backgroundTask.cancel(true);
它明确告诉工作人员通过 .. 中断线程来取消.从它的 api 文档:
which explicitly tells the worker to cancel by .. interrupting the thread. From its api doc:
mayInterruptIfRunning - 如果执行此任务的线程应该被中断，则为 true；否则，允许完成正在进行的任务
mayInterruptIfRunning - true if the thread executing this task should be interrupted; otherwise, in-progress tasks are allowed to complete
顺便说一句:捕获异常并且什么都不做(从而有效地忽略中断)并不是最好的想法.在这种情况下可能不会造成太大的破坏 - 由于检查了取消的状态.典型的工作实现要么在需要时进行一些内部清理之后捕获并返回，要么根本不处理它.
As an aside: catching the exception and doing nothing (thereby effectively ignoring the interrupt) is not the best of ideas. Probably not too damaging in this case - due to checking the cancelled status. Typical worker implementations either catch and return, after doing some internal cleanup if needed, or don't handle it at all.
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