What does this boolean “(number & 1) == 0” mean?

Question

On CodeReview I posted a working piece of code and asked for tips to improve it. One I got was to use a boolean method to check if an ArrayList had an even number of indices

Answer 1

& is a bitwise AND operation.

For number = 8:

  1000
  0001
& ----
  0000

The result is that (8 & 1) == 0. This is the case for all even numbers, since they are multiples of 2 and the first binary digit from the right is always 0. 1 has a binary value of 1 with leading 0s, so when we AND it with an even number we're left with 0.