Why Long.toHexString(0xFFFFFFFF) returns ffffffffffffffff

Question

This is what I see in java, and it puzzles me.

Long.toHexString(0xFFFFFFFF) returns ffffffffffffffff

Similarly, 0xFFFFFFFF

Answer 1

0xFFFFFFFF is an int literal. When using ints (32 bit in Java) 0xFFFFFFFF equals -1. What your code does:

• the compiler parses 0xFFFFFFFF as an int with value -1
• the java runtime calls Long.toHexString(-1) (the -1 get "casted" automatically to a long which is expected here)

And when using longs (64 bit in Java) -1 is 0xffffffffffffffff.

long literals are post-fixed by an L. So your expected behaviour is written in Java as:

Long.toHexString(0xFFFFFFFFL)

and Long.toHexString(0xFFFFFFFFL) is "ffffffff"