look in java int to String or vice verse is not possible. but in place of " " if u place ' ' and in place of String if u place char data type then ur code look like this ((int)((char)((int)'7')+'5')) and it is a valid expression which mean is that
"1st u r converting char 7 to its equivalent int type= 55 and char value of 5 is 53 then both 53 and 55 is added result 108 is converted to char again its converted to int so output is 108
but according to ur question it will give compile time error "inconvertible types" it is not an Exception
There is lot of difference between Compile time error and Exception