@Override
	public boolean equals(Object o) {
		if ( o==null || !(o instanceof Interval) ) {
			return false;
		}
		Interval other = (Interval)o;
		return this.a==other.a && this.b==other.b;
	}
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