Question

获取

"Exception in thread "AWT-EventQueue-1" java.lang.NullPointerException"

在所有soms1.actionPerformed行事件的ActionListener处：

 thread.set_state(1);
 thread.set_state(2);
 thread.reset;
 thread.send;

你能否建议在线程中获取空值的位置？此代码以前运行良好，但在代码中发生少量更改后出现此错误。

代码段：

public class soms1 extends JApplet {

static public SOM_thread1 thread = null;
static JApplet japplet = new JApplet();

static JButton go1 = new JButton("go");
static JButton play = new JButton("play");
static JButton reset = new JButton("Reset");
static JButton send = new JButton("send");

static Container c;
static JPanel p1 = new JPanel();
static JPanel p2 = new JPanel();
static JPanel p6 = new JPanel();

Toolkit tool;

public void setup_applet() {
    japplet.setVisible(true);

    go1.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {thread.set_state(1);}
    });
    play.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {thread.set_state(2);}
    });
    reset.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {thread.reset();}
    });
    send.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {thread.send();}
    });
}

public void init() {
    tool = Toolkit.getDefaultToolkit();
    setup_applet();
    setup_radios();
    setup_layout();

    thread = new SOM_thread1();
    thread.init();
    thread.start();
    if (clientSocket != null) {thread.set_state(2);}
   }
}

class SOM_thread1 extends Thread{
public void set_state(int f) {state = f;}
public void send() { //code block}
public void reset() {//code block}
public void run() {//code block}
public void init() {reset();}
}

因为我是java的新手，请建议更改提前谢谢你。

Answer 1

在初始化init函数内的线程之前，您正在调用setup_applet。

替换此

public void init() { 
     tool = Toolkit.getDefaultToolkit();
     setup_applet();
     setup_radios();
     setup_layout();
     thread = new SOM_thread1(); 
     thread.init(); 
     thread.start();
     if (clientSocket != null) {
          thread.set_state(2);
           }
       } 
  }

有了这个

public void init() { 
     tool = Toolkit.getDefaultToolkit();
     thread = new SOM_thread1();
     setup_applet();
     setup_radios();
     setup_layout(); 
     thread.init(); 
     thread.start();
     if (clientSocket != null) {
          thread.set_state(2);
           }
       }

（注意init函数末尾的删除}。还有一个）

另外将线程方法中的}与另一行分开，因为你用//

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在ActionListener上获取java.lang.NullPointerException

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