Assuming you mean the largest negative, non-infinite number, sounds correct because, for floating point numbers in 64-bit IEEE 754 floating point (which is what Java uses for doubles):
- The size of the number is stored in one part of the binary rep
- The sign of the number is stored in a separate part of the binary rep
Therefore:
The largest representable negative number would be the same as the largest representable positive number with the sign bit flipped to indicate a negative number.