Your code fails because it tries to parse a number that would require 33 bits to store as a signed integer.
A signed int
is a 32 bit value in two's complement representation, where the first bit will indicate the sign of the number, and the remaining 31 bits the value of the number. (-ish.) Java only supports signed integers, and parseInt()
and friends aren't supposed to parse two's complement bit patterns – and thus interpret the 1
or (possibly implied) 0
at the 32nd position from the right as the sign. They're meant to support parsing a human-readable reprentation, which is an optional -
(or +
) for the sign, followed by the absolute value of a number.
In this context, it's a false intuition that leads you to expect the behaviour you describe: if you were parsing any other base besides base 2 (or maybe the other commonly used power-of-two bases), would you expect the first digit of the input to affect the sign? Obviously you wouldn't; having, say, parseInt("2147483648")
return -2147483648
by design would be PHP levels of crazy.
Special-casing power-of-two bases also feels odd. Better to have a separate approach to handling bit patterns, for example the one in this answer.
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