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Execution sequence of try catch finally with return

2022-07-22 12:06:00 【InfoQ】

argument

No matter if there is any abnormality ,finally All the code in the block will execute ;

When try and catch There is return when ,finally Still execute ;

finally Is in return The following expression is evaluated （ The calculated value is not returned , Instead, save the value you want to return , tube finally What about the code in , The value returned will not change , It's still the value that we saved before ）, So the return value of the function is at finally Determined before execution ;

finally It is best not to include return, Otherwise the program will exit early , The return value is not try or catch The return value saved in .

argument

situation 1

：try{} catch(){}finally{} return;

             Obviously the program runs in sequence .

situation 2

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

           Program execution try In block return Before （ Include return Expression operations in statements ） Code ;

          Re execution finally block , Finally, execute try in return;

         finally Statement after block return, Because the program is try Already in the return So no more execution .

situation 3

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

          Program first try, If an exception is encountered catch block ,

          There are abnormal ： execute catch in return Before （ Include return Expression operations in statements ） Code , Re execution finally All the code in the statement , Finally, execute catch In block return. finally After that 4 The code at .

          No abnormality ： After execution try Again finally Again return.

situation 4

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

           Program execution try In block return Before （ Include return Expression operations in statements ） Code ;

           Re execution finally block , because finally In the block return So exit early .

situation 5

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

           Program execution catch In block return Before （ Include return Expression operations in statements ） Code ;

           Re execution finally block , because finally In the block return So exit early .

situation 6

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

           Program execution try In block return Before （ Include return Expression operations in statements ） Code ;

           There are abnormal ： perform catch In block return Before （ Include return Expression operations in statements ） Code ; Is to perform finally block , because finally In the block return So exit early .

           No abnormality ： Is to perform finally block , because finally In the block return So exit early .

summary

Any implementation try  perhaps catch Medium return The statement before , Will execute first finally sentence , If finally exist . If finally There is return sentence , So the program is return 了 , therefore finally Medium return Is bound to be return Of , The compiler the finally Medium return Implemented as a warning.

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