Question

Why are this two methods using two different approaches while processing binary numbers? String which represents negative binary number in Integer.parseInt(String s, 2) method should start with - character, but Integer.toBinaryString(int i) returns string with additional 1 ahead. So, this code

Integer.parseInt(Integer.toBinaryString(-1), 2);

throws java.lang.NumberFormatException. What is the reason of such behavior?

Answer 1

This is by design; Integer.toBinaryString

Returns a string representation of the integer argument as an unsigned integer in base 2.

(emphasis added).

I.e., toBinaryString provides a way to format an integer as the common two’s complement representation, which is the way most processors actually store signed integers internally.