首页
登录 | 注册

关于Java中try-catch-finally-return的执行顺序

1、try块中没有抛出异常,try、catch和finally块中都有return语句
   
public static int NoException(){
         int i=10;
         try{
           System.out.println("i in try block is:"+i);
           return --i;
         }
         catch(Exception e){
           --i;
           System.out.println("i in catch - form try block is:"+i);
           return --i;
         }
         finally{     
           System.out.println("i in finally - from try or catch block is:"+i);
           return --i;
         }  
}

运行代码:
   
public static void main(String[] args) {
        System.out.println("=============NoException==================");
        System.out.println(NoException());
        System.out.println("===============================");   
}

运行结果:
   
=============NoException==================
i in try block is:10
i in finally - from try or catch block is:9
8
===============================


执行顺序:

   执行try块,执行到return语句时,先执行return的语句,--i,但是不返回到main方法,执行finally块,遇到finally块中的return语句,执行--i,并将值返回到main方法,这里就不会再回去返回try块中计算得到的值。

结论:try-catch-finally都有return语句时,没有异常时,返回值是finally中的return返回的。


2.try块中没有抛出异常,仅try和catch中有return语句
   
public static int NoException1(){
            int i=10;
            try{
                System.out.println("i in try block is:"+i);
                return --i;
            }
            catch(Exception e){
                --i;
                System.out.println("i in catch - form try block is:"+i);
                return --i;
            }
            finally{           
                System.out.println("i in finally - from try or catch block is:"+i);
                --i;
                System.out.println("i in finally block is:"+i);
                //return --i;
            }
}

运行结果:
   
=============NoException1==================
i in try block is:10
i in finally - from try or catch block is:9
i in finally block is:8
9
===============================

执行顺序:

   try中执行完return的语句后,不返回,执行finally块,finally块执行结束后,返回到try块中,返回i在try块中最后的值。

结论:try-catch都有return语句时,没有异常时,返回值是try中的return返回的。


3.try块中抛出异常,try、catch和finally中都有return语句
   
public static int WithException(){
            int i=10;
            try{
                System.out.println("i in try block is:"+i);
                i = i/0;
                return --i;
            }
            catch(Exception e){
                System.out.println("i in catch - form try block is:"+i);
                --i;
                System.out.println("i in catch block is:"+i);
                return --i;
            }
            finally{           
                System.out.println("i in finally - from try or catch block is--"+i);
                --i;
                System.out.println("i in finally block is--"+i);
                return --i;
            }
}

执行结果:
   
=============WithException==================
i in try block is:10
i in catch - form try block is:10
i in catch block is:9
i in finally - from try or catch block is--8
i in finally block is--7
6
===============================

执行顺序:

   抛出异常后,执行catch块,在catch块的return的--i执行完后,并不直接返回而是执行finally,因finally中有return语句,所以,执行,返回结果6。

结论:

   try块中抛出异常,try、catch和finally中都有return语句,返回值是finally中的return。


4.try块中抛出异常,try和catch中都有return语句
   
public static int WithException1(){
            int i=10;
            try{
                System.out.println("i in try block is:"+i);
                i=i/0;
                return --i;
            }catch(Exception e){
                System.out.println("i in catch - form try block is:"+i);           
                return --i;
            }finally{
                                                                                                                                                                      
                System.out.println("i in finally - from try or catch block is:"+i);
                --i;
                System.out.println("i in finally block is:"+i);
                //return i;
            }
}

执行结果:
   
=============WithException1==================
i in try block is:10
i in catch - form try block is:10
i in finally - from try or catch block is:9
i in finally block is:8
===============================

执行顺序:

   抛出异常后,执行catch块,执行完finally语句后,依旧返回catch中的执行return语句后的值,而不是finally中修改的值。

结论:

   返回的catch中return值。


5.try、catch中都出现异常,在finally中有返回

public static int WithException2(){
            int i=10;
            try{
                System.out.println("i in try block is:"+i);
                i=i/0;
                return --i;
            }
            catch(Exception e){
                System.out.println("i in catch - form try block is:"+i);
                int j = i/0;
                return --i;
            }
            finally{
                                                                                       
                System.out.println("i in finally - from try or catch block is:"+i);
                --i;
                --i;
                System.out.println("i in finally block is:"+i);
                return --i;
}

执行结果:
   
=============WithException2==================
i in try block is:10
i in catch - form try block is:10
i in finally - from try or catch block is:10
i in finally block is:8
===============================

执行顺序:  

   try块中出现异常到catch,catch中出现异常到finally,finally中执行到return语句返回,不检查异常。

结论:

   返回finally中return值。


6、只在函数最后出现return语句
   
public static int WithException3(){
            int i=10;
            try{
                System.out.println("i in try block is:"+i);
                i=i/0;
                //return --i;
            }
            catch(Exception e){
                System.out.println("i in catch - form try block is:"+i);
                //int j = i/0;
                //return --i;
            }
            finally{
                                                                          
                System.out.println("i in finally - from try or catch block is:"+i);
                --i;
                --i;
                System.out.println("i in finally block is:"+i);
                //return --i;
            }
            return --i;
}

执行结果:
=============WithException3==================
i in try block is:10
i in catch - form try block is:10
i in finally - from try or catch block is:10
i in finally block is:8
7
===============================


总体结论:

结论一:

   return语句并不是函数的最终出口,如果有finally语句,这在return之后还会执行finally(return的值会暂存在栈里面,等待finally执行后再返回)
结论二:

   finally里面不建议放return语句,根据需要,return语句可以放在try和catch里面和函数的最后。可行的做法有四:
   (1)return语句只在函数最后出现一次。
   (2)return语句仅在try和catch里面都出现。
   (3)return语句仅在try和函数的最后都出现。
   (4)return语句仅在catch和函数的最后都出现。
   注意,除此之外的其他做法都是不可行的,编译器会报错。

相关文章

  • Java中String的substring函数(转载)
    你了解Java中String的substring函数吗? Java中的substring函数是我们经常使用的一个函数,用来截取当前字符串的子串,定义如下: public final class String{ public String s ...
  • Java中Uuid的实现   2008-05-30 15:28:38|  分类: JAVA相关 |  标签: |字号大中小 订阅 1.一种Native的实现,产生真正的Uuid,好像用的人挺多的.http://www.doomdark.or ...
  • 经作者同意转载自  http://blog.csdn.net/xrbeck现在的开发工具比较多,如JAVA,C++,.NET等,如何在这些不同的开发工具中实现代码的复用,成为一个比较重要的话题,也是提高生产率,降低项目成本的一个重要手段.其 ...
  • 具体代码在我的GitHub中可以找到 文章首发于我的个人博客: 代码块:用{}包围的代码 局部代码块 public class 局部代码块 { @Test public void test (){ B b = new B(); b.go() ...
  • 在JAVA中用json-lib-2.3-jdk15.jar包中提供了JSONObject和JSONArray基类,用于JSON的序列化和反序列化的操作.但是我们更习惯将其进一步封装,达到更好的重用. 封装后的JSON工具类JSONUtils ...
  • http://blog.csdn.net/luoweifu/article/details/46613015 原文:http://blog.csdn.net/luoweifu/article/details/46613015 作者:luow ...

2020 unjeep.com webmaster#unjeep.com
12 q. 0.015 s.
京ICP备10005923号