Analysis of java thread group and unhandled exception instances

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A finishing touch

From jdk1 Starting from 5, Java has strengthened the exception handling of threads. If an unhandled exception is thrown during thread execution, the JVM will automatically find out whether there is a corresponding thread before ending the thread Uncaughtexceptionhandler object. If the processor object is found, the uncaughtexception (thread T, throwable E) method of the object will be called to handle the exception.

Thread. Uncaughtexceptionhandler is an internal public static interface of thread class. There is only one method in this interface: void uncaughtexception (thread T, throwable E). T in this method represents the thread with exception, and e represents the exception thrown by this thread.

Default process for thread group exception handling:

1 if the thread group has a parent thread group, call the uncaughtexception method of the parent thread group to handle the exception.

2 if the thread class to which the thread instance belongs has a default exception handler (the exception handler set by the setdefaultuncaughtexceptionhandler method), call the exception handler to handle the exception.

3. If the exception object is a ThreadDeath object, no processing will be performed; Otherwise, the information of the exception tracking stack will be printed to system Err error output stream and end the thread.

II. Actual combat

1 code

// 定义自己的异常处理器
class MyExHandler implements Thread.UncaughtExceptionHandler
{
   // 实现uncaughtException方法，该方法将处理线程的未处理异常
   public void uncaughtException(Thread t,Throwable e)
   {
      System.out.println(t + " 线程出现了异常：" + e);
   }
}
public class ExHandler
{
   public static void main(String[] args)
   {
      // 设置主线程的异常处理器
      Thread.currentThread().setUncaughtExceptionHandler
        (new MyExHandler());
      int a = 5 / 0;   // ①
      System.out.println("程序正常结束！");
   }
}

2 operation

3 description

The exception handler specified by the program handled the uncapped exception, but the program will not end normally. This shows that the exception handler is different from catching exceptions through catch - when using catch to catch exceptions, exceptions will not be passed up to the upper level caller, but after using the exception handler to handle exceptions, exceptions will still be passed to the upper level caller.

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