try与finally块中return的有关问题

try与finally块中return的问题

今天在网上看到相关的文章，复制好的
情况1：try{} catch(){} finally{} return;

package?com.lwf.eus.servlet; public?class?Test{??
1. ????public?static?void?main(String[]?args){ ?????????System.out.print(tt());???
2. ????}??? ????public?static?int?tt(){???
3. ?????????int?b?=?23;??? ?????????try{???
4. ?????????????System.out.println("yes"); ?????????????b?+=?88;
5. ?????????}catch(Exception?e){??? ?????????????System.out.println("error?:"?+?e);
6. ?????????}finally{??? ??????????????if(b>25){???
7. ??????????????????System.out.println("b>25?:"+b);??? ??????????????}???
8. ??????????????System.out.println("finally");??? ?????????}
9. ????????? ?????????return?101;?????????????//---4
10. ????} }
    

显然程序按顺序执行，最后return 101退出
结果：

yes
1. b>25?:111 finally
2. 101

情况2:try{ return; } catch(){} finally{} return;

package?com.lwf.eus.servlet; public?class?Test{??
1. ????public?static?void?main(String[]?args){ ?????????System.out.print(tt());???
2. ????}??? ????public?static?int?tt(){???
3. ?????????int?b?=?23;??? ?????????try{???
4. ?????????????System.out.println("yes"); ?????????????b?+=?88;
5. ?????????????return?b;????????????//---1 ?????????}catch(Exception?e){???
6. ?????????????System.out.println("error?:"?+?e); ?????????}finally{???
7. ??????????????if(b>25){??? ??????????????????System.out.println("b>25?:"+b);???
8. ??????????????}??? ??????????????System.out.println("finally");???
9. ?????????} ?????????
10. ?????????return?101;?????????????//---4 ????}
11. }

程序执行try块中return之前（包括return语句中的表达式运算）代码；再执行finally块，最后执行try中return;
finally块之后的语句，这里的4处return，因为程序在1处已经return所以不再执行。
结果：

yes
1. b>25?:111 finally
2. 111

情况3:try{ } catch(){ return;} finally{} return;

package?com.lwf.eus.servlet; public?class?Test{??
1. ????public?static?void?main(String[]?args){ ?????????System.out.print(tt());???
2. ????}??? ????public?static?int?tt(){???
3. ?????????int?b?=?23;??? ?????????try{???
4. ?????????????System.out.println("yes"); ?????????????b?+=?88;
5. ?????????}catch(Exception?e){??? ?????????????System.out.println("error?:"?+?e);
6. ?????????????return?b;????????????//---2 ?????????}finally{???
7. ??????????????if(b>25){??? ??????????????????System.out.println("b>25?:"+b);???
8. ??????????????}??? ??????????????System.out.println("finally");???
9. ?????????} ?????????
10. ?????????return?101;?????????????//---4 ????}
11. }

程序先执行try，如果遇到异常执行catch块，
??? 有异常：则执行catch中return之前（包括return语句中的表达式运算）代码，再执行finally语句中全部代码，最后执行
catch块中return. finally之后也就是4处的代码不再执行。
??? 无异常：执行完try再finally再return.
结果：本次为无异常结果（当然本示例没有设计异常）

yes
1. b>25?:111 finally
2. 101

情况4:try{ return; } catch(){} finally{return;}

package?com.lwf.eus.servlet; public?class?Test{??
1. ????public?static?void?main(String[]?args){ ?????????System.out.print(tt());???
2. ????}??? ????public?static?int?tt(){???
3. ?????????int?b?=?23;??? ?????????try{???
4. ?????????????System.out.println("yes"); ?????????????b?+=?88;
5. ?????????????return?b;????????????//---1 ?????????}catch(Exception?e){???
6. ?????????????System.out.println("error?:"?+?e); ?????????}finally{???
7. ??????????????if(b>25){??? ??????????????????System.out.println("b>25?:"+b);???
8. ??????????????}??? ??????????????System.out.println("finally");???
9. ??????????????return?100;????????//---3 ?????????}
10. ????????? ????}
11. }

程序执行try块中return之前（包括return语句中的表达式运算）代码；再执行finally块，因为finally块中有return所以提前退出
结果：

yes
1. b>25?:111 finally
2. 100

情况5:try{} catch(){return;} finally{return;}

package?com.lwf.eus.servlet; public?class?Test{??
1. ????public?static?void?main(String[]?args){ ?????????System.out.print(tt());???
2. ????}??? ????public?static?int?tt(){???
3. ?????????int?b?=?23;??? ?????????try{???
4. ?????????????System.out.println("yes"); ?????????????b?+=?88;
5. ?????????}catch(Exception?e){??? ?????????????System.out.println("error?:"?+?e);
6. ?????????????return?b;????????????//---2 ?????????}finally{???
7. ??????????????if(b>25){??? ??????????????????System.out.println("b>25?:"+b);???
8. ??????????????}??? ??????????????System.out.println("finally");???
9. ??????????????return?100;????????//---3 ?????????}
10. ????????? ????}
11. }

程序执行catch块中return之前（包括return语句中的表达式运算）代码；再执行finally块，因为finally块中有return所以提前退出
结果：

yes
1. b>25?:111 finally
2. 100

情况6:try{ return;} catch(){return;} finally{return;}

package?com.lwf.eus.servlet; public?class?Test{??
1. ????public?static?void?main(String[]?args){ ?????????System.out.print(tt());???
2. ????}??? ????public?static?int?tt(){???
3. ?????????int?b?=?23;??? ?????????try{???
4. ?????????????System.out.println("yes"); ?????????????b?+=?88;
5. ?????????????return?b;????????????//---1 ?????????}catch(Exception?e){???
6. ?????????????System.out.println("error?:"?+?e); ?????????????return?b;????????????//---2
7. ?????????}finally{??? ??????????????if(b>25){???
8. ??????????????????System.out.println("b>25?:"+b);??? ??????????????}???
9. ??????????????System.out.println("finally");??? ??????????????return?100;????????//---3
10. ?????????} ?????????
11. ????} }

程序执行try块中return之前（包括return语句中的表达式运算）代码；
?? 有异常:执行catch块中return之前（包括return语句中的表达式运算）代码；则再执行finally块，因为finally块中有return所以提前退出
?? 无异常：则再执行finally块，因为finally块中有return所以提前退出
无异常结果：

yes
1. b>25?:111 finally
2. 100

以下情况
情况1：try{} catch(){} finally{} return;
情况2:try{ return; } catch(){} finally{} return;
情况3:try{} catch(){ return;} finally{} return;
情况4:try{ return; } catch(){} finally{return;}
情况5:try{} catch(){return;} finally{return;}
情况6:try{ return;} catch(){return;} finally{return;}

以上几种情况说明：
一、如果try catch finally块均无return则执行最后finally外的return；如果try catch finally中任何一个有return则最后finally外的return不再执行；
二、只要finally块中有return则try或catch中的return不再执行

以下几种情况在finally块的后面是不能出现return的。
情况:try{} catch(){} finally{ return;} return;
情况:try{ return; } catch(){} finally{return;} return;
情况:try{} catch(){return;} finally{return;} return;
情况:try{ return; } catch(){return;} finally{} return;
情况:try{ return; } catch(){return;} finally{return;} return;

上面几种情况因为finally块中已有return，而且是必须执行的，所以finally外的return必定不能执行，所以编译器提示错误。特殊的 try{ return; } catch(){return;} finally{} return;是因为try和catch中都有return所以必定会执行其中一个，所以finally外的return不能执行，所以编译器提示错误。

还有一种情况：


最终结论：任何调用try 或者catch中的return语句之前，都会先执行finally语句，如果finally存在的话。如果finally中有return语句，那么程序就return了，所以finally中的return是一定会被return的，编译器把finally中的return实现为一个warning。