Java SwingWorker Flicker

Question

有人能告诉我为什么在这个使用SwingWorker的简单演示中，屏幕会像按钮不断跳跃一样闪烁吗？ （关于改进多线程部分的反馈也很受欢迎）。

import java.awt.EventQueue;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Calendar;
import java.util.List;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingWorker;

public class SwingWorkerStopWatch extends JFrame{
    JButton jbStart,jbStop;
    JLabel jlStatus;
    Long startTime;
    SwingWorker<Double, Double> SW;

    public SwingWorkerStopWatch() {
        setLayout(new FlowLayout());
        setSize(240, 100);

        jlStatus = new JLabel("Press Start");

        jbStart = new JButton("Start");
        jbStop = new JButton("Stop");

        jbStop.setEnabled(false);

        jbStart.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                startTime = Calendar.getInstance().getTimeInMillis();
                jbStart.setEnabled(false);
                jbStop.setEnabled(true);
                SW = new StopWatchSwingWorker();
                SW.execute();
            }
        });

        jbStop.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                SW.cancel(true);
                Long stopTime = Calendar.getInstance().getTimeInMillis();
                Double elapsedTime = (double)(stopTime-startTime)/1000;
                jlStatus.setText("Elapsed time is: " + elapsedTime);
                jbStart.setEnabled(true);
                jbStop.setEnabled(false);
            }
        });

        add(jbStart);
        add(jbStop);
        add(jlStatus);

        //pack();
    }

    private class StopWatchSwingWorker extends SwingWorker<Double, Double>{

        @Override
        protected Double doInBackground() throws Exception {
            Long tempTime;

            while (true) {
                tempTime = Calendar.getInstance().getTimeInMillis();
                Double elapsedTime = (double)(tempTime-startTime)/1000;
                publish(elapsedTime);
            }
        }

        @Override
        protected void process(List<Double> chunks) {
            if (isCancelled()) {
                return;
            }
            jlStatus.setText("" + chunks.get(chunks.size()-1));
        }

    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                JFrame stopWatchFrame = new SwingWorkerStopWatch();
                stopWatchFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                stopWatchFrame.setVisible(true);
            }
        });
    }
}

Answer 1

它与SwingWorker无关，而与组件如何响应其布局有关。数字字符串的宽度会有变化，如果它的尾部为0，导致JLabel改变宽度，导致跳跃，因此您应该使用String.format(...)或DecimalFormat对象格式化数字String，使其具有恒定的宽度。

例如

如，

  @Override
  protected void process(List<Double> chunks) {
     if (isCancelled()) {
        return;
     } else {
        String numberTxt = String.format("%5.3f",
              chunks.get(chunks.size() - 1));
        jlStatus.setText(numberTxt);
     }

     // jlStatus.setText("" + chunks.get(chunks.size() - 1));
     // System.out.println(chunks.get(chunks.size() - 1));
  }