Bitwise negation gives unexpected result

Question

I am trying to write a bitwise calculator in java, something that you could input an expression such as ~101 and it would give back 10 however when i run this code

Answer 1

If a = ...0000101 (bin) = 5 (dec)

~a = ~...0000101(bin) = ...1111010(bin) 

and Java uses "Two's complement" form to represent negative numbers so

~a = -6 (dec)

Now difference between Integer.toBinaryString(number) and Integer.toString(number, 2) for negative number is that

• toBinaryString returns String in "Two's complement" form but
• toString(number, 2) calculates binary form as if number was positive and add "minus" mark if argument was negative.

So toString(number, 2) for ~a = -6 will

1. calculate binary value for 6 -> 0000110,
2. trim leading zeros -> 110,
3. add minus mark -> -110.