Method headMap

lib/java/util/TreeMap.java:595–601

(K endKey)

        }

        public SortedMap<K, V> headMap(K endKey) {
            checkRange(endKey);
            if (hasStart) {
                return new SubMap<K, V>(startKey, backingMap, endKey);
            }
            return new SubMap<K, V>(backingMap, endKey);
        }

        @Override
        public boolean isEmpty() {