### Question:
HMapKL implements MapKL<K>, Cloneable, Serializable { @Override public void plus(MapKL<K> m) { for (MapKL.Entry<K> e : m.entrySet()) { K key = e.getKey(); if (this.containsKey(key)) { this.put(key, (long) (this.get(key) + e.getValue())); } else { this.put(key, e.getValue()); } } } @SuppressWarnings("unchecked")  HMapKL(int initialCapacity, float loadFactor);  HMapKL(int initialCapacity); @SuppressWarnings("unchecked")  HMapKL();  HMapKL(MapKL<? extends K> m); int size(); boolean isEmpty(); long get(K key); boolean containsKey(K key); long put(K key, long value); void putAll(MapKL<? extends K> m); long remove(K key); void clear(); boolean containsValue(long value); @SuppressWarnings("unchecked") Object clone(); Set<K> keySet(); Collection<Long> values(); Set<MapKL.Entry<K>> entrySet(); String toString(); @Override void plus(MapKL<K> m); @Override long dot(MapKL<K> m); @Override void increment(K key); @Override void increment(K key, long value);  }### Answer:
@Test public void testPlus() throws IOException { HMapKL<String> m1 = new HMapKL<String>(); m1.put("1", Integer.MAX_VALUE + 5L); m1.put("2", Integer.MAX_VALUE + 22L); m1.put("" + Integer.MAX_VALUE, Integer.MAX_VALUE); HMapKL<String> m2 = new HMapKL<String>(); m2.put("1", 4L); m2.put("3", Integer.MAX_VALUE + 5L); m2.put("" + Integer.MAX_VALUE, Integer.MAX_VALUE); m1.plus(m2); assertEquals(m1.size(), 4); assertTrue(m1.get("1") == Integer.MAX_VALUE + 9L); assertTrue(m1.get("2") == Integer.MAX_VALUE + 22L); assertTrue(m1.get("3") == Integer.MAX_VALUE + 5L); assertTrue(m1.get("" + Integer.MAX_VALUE) == 2L * Integer.MAX_VALUE); }