But still under confusion,as where does this invertion come into action...
If i replace the number in the code to 5 or 6 or 7,the output gives a +1 to the number with a negative sign.

For eg: if i replace it with say 6 now...
I get the output as -7

1) the '~' inverts all the bits. Since a '4' is represented as

00000000 00000000 00000000 00000100

when you invert the bits you get

11111111 11111111 11111111 11111011

2) now you need to understand how java interprets this value. google or search this forum for "two's complement". basically, you look a the left-most digit, and if it's a 1, you know your value will be negative. you then invert all the digits and add one, so you get

which is 5. and we know our answer is negative, so "11111111 11111111 11111111 11111011" = -5.

There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors