Java第五讲异常处理总结

1.

在运行上述代码时javac产生idiv字节码指令，在运行下面的程序时javac产生ddiv字节指令，导致了两段代码运行结果不同。

2.

3.finally语句块一定会执行吗？

/**
 * 自定义的异常类
 * @author JinXuLiang
 *
 */
class MyException extends Exception
{
    public MyException(String Message) {
        super(Message);
    }
    public MyException(String message, Throwable cause) {
        super(message, cause);
    }
     public MyException( Throwable cause) {
        super(cause);
    }

}

public class ExceptionLinkInRealWorld {
   public static void main( String args[] )
   {
      try {
         throwExceptionMethod();  //有可能抛出异常的方法调用
      }
      catch ( MyException e )
      {
         System.err.println( e.getMessage() );
         System.err.println(e.getCause().getMessage());
      }
      catch ( Exception e )
      {
         System.err.println( "Exception handled in main" );
      }
      doesNotThrowException(); //不抛出异常的方法调用
   }

   public static void throwExceptionMethod() throws MyException
   {

      try {
         System.out.println( "Method throwException" );

         throw new Exception("系统运行时引发的特定的异常");  // 产生了一个特定的异常
      }
      catch( Exception e )
      {
         System.err.println(
            "Exception handled in method throwException" );
         //转换为一个自定义异常，再抛出
         throw new MyException("在方法执行时出现异常",e);

      }
      finally {
         System.err.println(
            "Finally executed in throwException" );
      }

      // any code here would not be reached
   }

   public static void doesNotThrowException()
   {
      try {
         System.out.println( "Method doesNotThrowException" );
      }
      catch( Exception e )
      {
         System.err.println( e.toString() );
      }
      finally {
         System.err.println(
            "Finally executed in doesNotThrowException" );
      }

      System.out.println(
         "End of method doesNotThrowException" );
   }
}

一般来说有两种情况finally不会运行：1.没运行到try-catch语句这里就返回了1）运行到try语句之前程序有了返回值，2）运行到try语句前程序报错，2.运行到try-catch语句了，但是没运行到finally代码块的时候，JVM就停止了在try语句运行的时候，直接把虚拟机退出了，如：System.exit(0);