Why is -1001 not a valid Java integer literal?

Question

In Java, -1001 is not considered a valid integer literal. Why?

Answer 1

There is no such thing as a negative decimal literal in Java; see JLS§3.10.1.

-1001 is an compile time evaluable constant expression consisting of a unary negation of the literal 1001.

(The same applies to C and C++).

Answer 2

The number -1001 is valid Integer literal in java 7 and above.