@Override
	public int hashCode() {
		int hash = 23;
		hash = hash * 31 + a;
		hash = hash * 31 + b;
		return hash;
	}
return number of elements between a and b inclusively. x..x is length 1.
 if b &lt; a, then length is 0.  9..10 has length 2.
runtime/Java/src/org/antlr/v4/runtime/misc/Interval.java