@Override
        public int hashCode() {
            return (this.key != null ? this.key.hashCode() : 0) ^
                   (this.value != null ? this.value.hashCode() : 0);
        }
Implementation of a Map that favors iteration speed rather than
get/put speed.

@author Kirill Vainer
jme3-core/src/main/java/com/jme3/util/ListMap.java