Question

Can anyone explain this to me ,

String str = "Hello";

str += ((char)97) +2; // str = "Hello99";

str = str +((char)97)+2; // str = "Helloa2";

does the += operator evaluate the right side first then it concatenate it with the left side ?

Answer 1

The difference has to do with the order of operations. The following:

str += ((char)97) +2; 

is equivalent to:

str = str + (((char)97) + 2);

On the other hand, the following:

str = str +((char)97)+2;

is equivalent to:

str = (str + ((char)97)) + 2;

Note the difference in the placement of parentheses.

Now let’s consider the two cases:

1) str = str + (((char)97) + 2):

Here, 97 + 2 is evaluated first. The result is an int (99), which is converted to string and appended to str. The result is "Hello99".

2) str = (str + ((char)97)) + 2:

Here, (char)97 ('a') is appended to the string, and then 2 is converted to string and appended to the result. This gives "Helloa2".