在JAVA中有两种异常:
- 非运行时异常(Checked Execption):这种异常必须在方法中声明throws语句指定,或者在方法体内捕获。例如IOException和ClassNotFoundException。
- 运行时异常(unChecked exception):这种异常不必在方法中声明指定,也不需要在方法体捕获。例如NumberFormatException。
因为run()方法不支持throws语句,所以当线程对象的run()方法抛出非运行异常时,我们必须捕获并且处理。在运行时异常从run()方法抛出时,默认行为是在控制台输出堆栈记录并退出程序。
public class ExceptionHandler implements UncaughtExceptionHandler { /** * Main method of the class. It process the uncaught excpetions throwed * in a Thread * @param t The Thead than throws the Exception * @param e The Exception throwed */ @Override public void uncaughtException(Thread t, Throwable e) { System.out.printf("An exception has been captured "); System.out.printf("Thread: %s ",t.getId()); System.out.printf("Exception: %s:%s ",e.getClass().getName(),e.getMessage()); System.out.printf("Stack Trace: "); e.printStackTrace(System.out); System.out.printf("Thread status: %s ",t.getState()); } }
/** * Runnable class than throws and Exception */ public class Task implements Runnable { @Override public void run() { // The next instruction always throws and exception int numero=Integer.parseInt("TTT"); } }
public class Main { /** * Main method of the example. Initialize a Thread to process the * uncaught exceptions and starts a Task object that always throws an * exception * @param args */ public static void main(String[] args) { Task task=new Task(); Thread thread=new Thread(task); thread.setUncaughtExceptionHandler(new ExceptionHandler()); thread.start(); try { thread.join(); } catch (InterruptedException e) { e.printStackTrace(); } System.out.printf("Thread has finished "); } }
工作原理:当一个线程抛出了异常并且没有捕获异常时,JVM检查这个线程是否设置了未捕获异常处理器。如果找到,JVM将调用这个线程对象的这个方法,并将线程对象和异常作为参数传入。
当线程抛出一个未捕获异常时,JVM将为异常寻找一下三种可能的处理:
首先,查找对象的未捕获异常处理器,如果找不着,JVM继续查找线程对象所在线程组的未捕获异常处理器。如果还找不到,JVM继续查找默认的未捕获异常处理器。如果没有一个处理器存在,JVM将堆栈异常记录打印到控制台,并退出程序。