Question

我对try，catch以及最后的Java有疑问。请考虑以下情形：

try{
//Some code here that throws IOExceotion
} 
catch (IOException ex){
System.out.println("Line 1: IOException Encountered!");
throw ex;
}
finally {
System.out.println("Line 2: I am always executed!");
}

上面代码段的输出是什么？我会看到：

Line 1: IOException Encountered!
Line 2: I am always executed!

还是

Line 2: I am always executed!
Line 1: IOException Encountered!

或者它只是（因为我们在catch块中抛出）

Line 1: IOException Encountered!

基本上，我没有找到一个示例，其中catch块中有一个“throw”，最后阻塞catch块（如上例所示）。任何人都可以对此有所了解吗？

感谢。

Answer 1

引用Java Language Specification, §14.20.4：

首先执行try块，执行带有finally块的try语句。然后有一个选择：

* If execution of the try block completes normally, then the finally block is executed, and then there is a choice:
      o If the finally block completes normally, then the try statement completes normally.
      o If the finally block completes abruptly for reason S, then the try statement completes abruptly for reason S. 
* If execution of the try block completes abruptly because of a throw of a value V, then there is a choice:
      o If the run-time type of V is assignable to the parameter of any catch clause of the try statement, then the first (leftmost) such catch clause is selected. The value V is assigned to the parameter of the selected catch clause, and the Block of that catch clause is executed. Then there is a choice:
            + If the catch block completes normally, then the finally block is executed. Then there is a choice:
                  # If the finally block completes normally, then the try statement completes normally.
                  # If the finally block completes abruptly for any reason, then the try statement completes abruptly for the same reason. 
            + If the catch block completes abruptly for reason R, then the finally block is executed. Then there is a choice:
                  # If the finally block completes normally, then the try statement completes abruptly for reason R.
                  # If the finally block completes abruptly for reason S, then the try statement completes abruptly for reason S (and reason R is discarded). 
      o If the run-time type of V is not assignable to the parameter of any catch clause of the try statement, then the finally block is executed. Then there is a choice:
            + If the finally block completes normally, then the try statement completes abruptly because of a throw of the value V.
            + If the finally block completes abruptly for reason S, then the try statement completes abruptly for reason S (and the throw of value V is discarded and forgotten). 
* If execution of the try block completes abruptly for any other reason R, then the finally block is executed. Then there is a choice:
      o If the finally block completes normally, then the try statement completes abruptly for reason R.
      o If the finally block completes abruptly for reason S, then the try statement completes abruptly for reason S (and reason R is discarded).

Answer 2

你会看到第一个。最后，块始终执行并作为最后一个。

Answer 3

这是一个流行测验吗？开玩笑。如果有异常，您将看到第一个。 finally块语句将始终执行，因此将始终打印。

Java中的异常处理

3 个答案: