Hi all, class test{ public static void main(String args[]){ int i = 1; System.out.println(~i); } } Output : -2 can someone kindly explain me what exactly ~ operator does ? thanks anand

~ just inverts all bits of the number In this case i=1 => 00000000 00000000 00000000 00000001 ~i => 11111111 11111111 11111111 11111110 And in binary ~1 equals -2. If you do Integer.parseInt("11111111111111111111111111111110",2); you'll get -2 More on binary: 2 in binary is 00000000 00000000 00000000 00000010 if you want to get the negative value of 2 you have to take the 2's complement of 2 which is just inverting all bits and adding 1. So if you invert it you get 11111111 11111111 11111111 11111101 and then you add one and you get 11111111 11111111 11111111 11111110 which is the same pattern as above and thus ~1 = -2 The genral rule is that ~i = -i-1 HIH ------------------ Valentin Crettaz Sun Certified Programmer for Java 2 Platform

Originally posted by Valentin Crettaz: And in binary ~1 equals -2.

Hi Valentin But I think ~1 in NOT equal to -2 in BINARY. It is the implementation of negative number which makes ~1 equal to -2, as neagtive numbers are stored as 2's compliment numbers. if we have lets say 4 bit integer size then -1 will be stored as : i) 1 in binary = 0001 ii) 2's compliment of 1 = 1111 (invert 0001, becomes 1110, add 1, becomes 1111); so -1 will be stored as 1111 (NOTE: MSB is '1'(on) which indicates that number is negative. 2's compliment is of positive number(eg. 1)) This is done for lot of reason, it makes airthmetic operation fasts(there are lot of algos for binary airthmetic), and it also makes -0 and +0 equal. I just want to say that it is the implementation which makes ~1 to equal to -2, in binary it will be some different number. CMIW AND thanks a lot for the general rule. It will really help us in binary questions in SCJP. ------------------ Regards Ravish [This message has been edited by ravish kumar (edited November 18, 2001).]

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