问答题

请完成下列Java程序；创建一个进度条，可以控制其开始和暂停。要求进度条与线程关联，由线程控制，点击Start按钮开始进度条的滚动，点击Stop按钮，暂停，继续点击Start按钮则继续进行。 注意：请勿改动main()主方法和其他已有语句内容，仅在下划线处填入适当的语句。 程序运行结果如下：
import javax．swing．*； import javax．swing．event．*； import java．awt．*； import java．awt．event．*； public class ex22_2 extends JPanel{ ThreadProg thProgress； JProgressBar jpb；//声明一个进程条对象 static JFrame if; public ex22_2() { setLayout(new BorderLayout())； jpb=new JProgressBar()； add(jpb，"Center")； JPanel btnPanel = new JPanel(); JButton btnStart = new JButton("Start"); btnPanel.add(btnStart); btnStart.addActionListener(new ActionListener() public void actionPerformed(ActionEvent ae) { _______________; } }); JButton btnStop = new JButton("Stop"); btnPanel.add(btnStop); btnStop.addActionListener(new ActionListener() public void actionPerformed(ActionEvent ae) { ____________; } }); add(btnPanel, BorderLayout. SOUTH); } public void startProgress() { if(thProgress == null|| !thProgress.isAlive()) thProgress = new ThreadProg(jpb); thProgress.start(); } } public void stopProgress() { thProgress.setStop(true); } public static void main(String args[]){ jf = new JFrame("ex22_2"); ex22_2 obj22_2 = new ex22_2(); jf.getContentPane().add("Center",obj22_2); jf.setSize(250,80); jf.addWindowListener(new WindowAdapter() { public void windowClosing(WindowEvent we) { System.exit(O); } }); jf.setVisible(true); } } class ThreadProg extends Thread { private JProgressBar jpb; private boolean bStop = false; private boolean bAlive = false; public ThreadProg(JProgressBar jpb){ this.jpb = jpb; } public void setStop(boolean b){ bStop = b; } public void run () { int min = 0; int max = 60; jpb.setMinimum(min); jpb.setMaximum(max); jpb.setValue(min); for (int x=min;x＜=max;x++) ( if(bStop){ break; }else{ jpb. setValue (x); try { Thread. sleep (150); } catch (InterruptedException e) { } } } bAlive = false; } }