volatile和synchronized关键字到底是用来干吗的？
怎样挂起(suspend)和恢复(resume)一个实现了runable接口的对象。

//synchronized多线程运行时用来同步，
//volatile我也不太清楚
//下面是一个应用suspend和resume的例子，
//希望对你有帮助：）

import java.awt.*;  
import java.awt.event.*;  
import javax.swing.*;  

public class VisualSuspendResume   
            extends JPanel   
            implements Runnable {  
    private static final String[] symbolList =   
            { "|", "/", "-", "\", "|", "/", "-", "\" };  

     private Thread runThread;  
     private JTextField symbolTF;  

     public VisualSuspendResume() {  
         symbolTF = new JTextField();   
         symbolTF.setEditable(false);  
         symbolTF.setFont(new Font("Monospaced", Font.BOLD, 26));  
         symbolTF.setHorizontalAlignment(JTextField.CENTER);  

         final JButton suspendB = new JButton("Suspend");  
         final JButton resumeB = new JButton("Resume");  
   
         suspendB.addActionListener(new ActionListener() {  
                 public void actionPerformed(ActionEvent e) {  
                     suspendNow();  
                 }  
             });  


         resumeB.addActionListener(new ActionListener() {  
                 public void actionPerformed(ActionEvent e) {  
                     resumeNow();  
                 }  
             });  

         JPanel innerStackP = new JPanel();  
         innerStackP.setLayout(new GridLayout(0, 1, 3, 3));  
         innerStackP.add(symbolTF);  
         innerStackP.add(suspendB);  
         innerStackP.add(resumeB);  

         this.setLayout(new FlowLayout(FlowLayout.CENTER));  
         this.add(innerStackP);  
     }  

     private void suspendNow() {  
         if ( runThread != null ) { // avoid NullPointerException  
             runThread.suspend();  
         }  
     }  


     private void resumeNow() {  
         if ( runThread != null ) { // avoid NullPointerException  
             runThread.resume();  
         }  
     }  


     public void run() {  
         try {  
             // Store this for the suspendNow() and   
             // resumeNow() methods to use.  
             runThread = Thread.currentThread();  
             int count = 0;  
             while ( true ) {  
                 // each time through, show the next symbol  
                 symbolTF.setText(  
                     symbolList[ count % symbolList.length ]);  
                 Thread.sleep(200);  
                 count++;  
             }  
         } catch ( InterruptedException x ) {  

            // ignore  
         } finally {  
             // The thread is about to die, make sure that the   
             // reference to it is also lost.  
             runThread = null;  
         }  
     }  

     public static void main(String[] args) {  
         VisualSuspendResume vsr = new VisualSuspendResume();  
         Thread t = new Thread(vsr);  
         t.start();  

 JFrame f = new JFrame("Visual Suspend Resume");  
         f.setContentPane(vsr);  
         f.setSize(320, 200);  
         f.setVisible(true);  
         f.addWindowListener(new WindowAdapter() {  
              public void windowClosing(WindowEvent e) {  
                     System.exit(0);  
                 }  
             });  
     }  
}