Java: What does ~ mean

The Tilde (~) performs a bitwise complement of a numerical value in Java.

See: Bitwise complement (~): inverts ones and zeroes in a number

It is the Unary ~ Bitwise complement operator (quoting) :

• only used with integer values
• inverts the bits ie a 0-bit becomes 1-bit and vice versa
• in all cases ~x equals (-x)-1

See also this page on Bitwise operators on wikipedia, which states :

The bitwise NOT, or complement, is a unary operation that performs logical negation on each bit, forming the ones' complement of the given binary value. Digits which were 0 become 1, and vice versa.
For example:

NOT 0111  (decimal 7)
  = 1000  (decimal 8)

In many programming languages (including those in the C family), the bitwise NOT operator is "~" (tilde).