Understand the execution process of try, catch and finally (including return) (the most detailed analysis of the whole network)

One 、 First , To determine these prerequisites, let's know ：
1、try Blocks must match catch Block or finally Block use , It can't be used alone
（ The normal use mode is divided into 3 Kind of ：①try+catch;②try+finally;③try+catch+finally）
2、 Under normal operation 、 Whether or not an exception is thrown 、 As long as the code has finally block , that finally Blocks are bound to execute , And finally Block is in try or catch Medium return After statement execution 、 Return to the previous execution （ The calculated value is not returned , Instead, save the value you want to return , No matter finally How about the code in the block , As long as there is no return sentence , Then the returned value will not change , Still before try perhaps catch The value stored in the block ）.
（ Be careful ： Under some abnormal circumstances , For example, in the implementation of finally Before the block , The virtual machine is terminated ; The thread where the program is located dies ;cpu Be closed in these cases ,finally Naturally, the block will not be executed ）
3、 When finally In the block return When the sentence is , Regardless of try and catch Is there a return sentence , The program will start from finally In the block return Statement returns , That is, the return value will also be finally In block return The return value of the statement , instead of try perhaps catch In the block .

Two 、 When try、catch、finally、return When used together , The implementation process of the code is explained in detail ：
（1）try{} catch(){}finally{} return;
Execute directly in the normal order .
（2）try{ return; }catch(){} finally{} return;
Execute first try In block return sentence , But it does not return a value ; And then execute finally Statement in block , And finally back to try in return Value ,finally After the block return Not execute , Because the program is already try The block return Back to .
（3） try{ } catch(){return;} finally{} return;
Execute first try block , Then see if there is any abnormality ：
In case of abnormality ： perform catch The block return But not back , Re execution finally block , And finally back to catach In the block return value .finally After return Don't execute .
If there is nothing unusual , Execute in order finally Block Zai return.
（4）try{ return; }catch(){} finally{return;}
perform try block return sentence （ Include return Expression operations in statements ）, But not back ;
Re execution finally block , perform finally block , Yes return, Back from here .
here finally The block return value , After the code is executed
（5） try{} catch(){return;}finally{return;}
There are abnormal ： Execute first try, Re execution catch Medium return But not back , Re execution finally In the block return, Back from here .
No abnormality ： Execute first try, Re execution finally block , Yes return, Back from here .
（6）try{ return;}catch(){return;} finally{return;}
First, the program executes try In block return sentence （ Include return Expression operations in statements ）, But not back ; Then see if there is any abnormality
There are abnormal ： perform catch In block return sentence （ Include return Expression operations in statements ）, But not back ;
Re execution finally block , Yes return, Back from here .
No abnormality ： Re execution finally block , Yes return, Back from here .

3、 ... and 、 summary
（1） Any implementation try perhaps catch Medium return After statement , Before returning , If finally exist , Will execute first finally sentence .
（2） 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.