java finally与return

 

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我们从几个问题开始：

一、finally一定会执行吗？

 

 

二、下面语句的执行结果是：

public class FinallyTest {

         public static void main(String[] args) {

                   System.out.println("getValue()返回值为:" + getValue());

         }

        

         public static int getValue() {

                   try {

                            return 0;

                   } finally {

                            return 1;

                   }

         }

}

 

 

三、下面语句的执行结果是：

public class FinallyTest {

         public static void main(String[] args) {

                   System.out.println("getValue()返回值为:" + getValue());

         }

        

         public static int getValue() {

                   int i = 1;

                   try {

                            return i;

                   } finally {

                            i++;

                   }

         }

}

 

 

 

首先，第一个问题，答案是否定的。在try里面执行了System.exit(0);操作finally就不会执行，另外死机、断电都会导致finally不会执行。

 

 

对于后面两个问题，我们先看一下摘自《THE Java™ Programming Language, Fourth Edition》By Ken Arnold, James Gosling, David Holmes中的几段话：

 

 

a finally clause is always entered with a reason. That reason may be that the try code finished normally, that it executed a control flow statement such as return, or that an exception was thrown in code executed in the TRy block. The reason is remembered when the finally clause exits by falling out the bottom. However, if the finally block creates its own reason to leave by executing a control flow statement (such as break or return) or by throwing an exception, that reason supersedes the original one, and the original reason is forgotten. For example, consider the following code:

try {

    // ... do something ...

    return 1;

} finally {

    return 2;

}

 

When the TRy block executes its return, the finally block is entered with the "reason" of returning the value 1. However, inside the finally block the value 2 is returned, so the initial intention is forgotten. In fact, if any of the other code in the try block had thrown an exception, the result would still be to return 2. If thefinally block did not return a value but simply fell out the bottom, the "return the value 1" reason would be remembered and carried out.

 

从红色和蓝色字体标注的解释可以看出，当finally中有return语句的时候，try中的return会被抛弃；当finally中没有return语句时，try中return的值会被保存且被返回。

 

 

所以，第二个问题的答案是：getValue()返回值为:1

 

第三个问题的答案是：getValue()返回值为:1

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