post increment behaviour [duplicate]

问题

i have small doubt.why the below code is printing value i=2.

int i=2;
i=i++;
System.out.println(i);

can someone please explain me what is happening in line no 2.

so there is no meaning here of doing ++ here?

Thanks

回答1:

i=i++;

Because first the assignment happens, then the increment applies.

Something like:

first i gets 2, then ++ operation happens, but results won't be re-assigned to i, so i value will remain as 2.

回答2:

i = i++; first evaluates the i++ expression, which increments i and evaluates to the value of i prior to the increment. Since you immediately assign to i this value, it resets the value of i so the increment appears to never have happened. i = ++i; would cause the other behavior.

回答3:

When you are telling i=i++; you are telling the computer to assign i to i, and after that, increment i's value, but it will not affect i, because i's value is 2.

The correct way to do it should be i=++i; meaning, add 1 to i before assigning it to i, or you could simply use i++;

回答4:

Thanks to all for helping me in understanding the things which was of great value.

I found somewhere nice post on this.

I got the answer from the suggestion given by stackoverflow forum only but there was some clear explanation missing what I feel.

Miljen Mikic suggested link is not working and saying page not found.

Some Clear explanation given for problem below is

int a=2, b=2;
int c = a++/b++;
System.out.println(c);

disassembles to the following.

   0:iconst_2      ; [I]Push the constant 2 on the stack[/I]  
   1:istore_1      ; [I]Pop the stack into local variable 1 (a)[/I]  
   2:iconst_2      ; [I]Push the constant 2 on the stack, again[/I]  
   3:istore_2      ; [I]Pop the stack into local variable 2 (b)[/I]  
   4:iload_1       ; [I]Push the value of a on the stack[/I]  
   5:iinc1, 1  ; [I]Add 1 to local variable 1 (a)[/I]  
   8:iload_2       ; [I]Push the value of b on the stack[/I]  
   9:iinc2, 1  ; [I]Add 1 to local variable 2 (b)[/I]  
   12:idiv          ; [I]Pop two ints off the stack, divide, push result[/I]  
   13:istore_3      ; [I]Pop the stack into local variable 3 (c)[/I]  
   14:return

which help me understand much better.

Please add to this If I am wrong in my point.

Thanks for all your answers.

来源：https://stackoverflow.com/questions/12147631/post-increment-behaviour

标签

java