For the detailed spec see 15.17.3. Remainder Operator % (the entire section 15.17 really) of The Java Language Specification
http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html
>
The binary % operator is said to yield the remainder of its operands from an implied division; the left-hand operand is the dividend and the right-hand operand is the divisor.
In C and C++, the remainder operator accepts only integral operands, but in the Java programming language, it also accepts floating-point operands.
The remainder operation for operands that are integers after binary numeric promotion (§5.6.2) produces a result value such that (a/b)*b+(a%b) is equal to a.
This identity holds even in the special case that the dividend is the negative integer of largest possible magnitude for its type and the divisor is -1 (the remainder is 0).
It follows from this rule that the result of the remainder operation can be negative only if the dividend is negative, and can be positive only if the dividend is positive. Moreover, the magnitude of the result is always less than the magnitude of the divisor.
If the value of the divisor for an integer remainder operator is 0, then an ArithmeticException is thrown.