### Question:
HMapKF implements MapKF<K>, Cloneable, Serializable { @Override public void plus(MapKF<K> m) { for (MapKF.Entry<K> e : m.entrySet()) { K key = e.getKey(); if (this.containsKey(key)) { this.put(key, this.get(key) + e.getValue()); } else { this.put(key, e.getValue()); } } } @SuppressWarnings("unchecked")  HMapKF(int initialCapacity, float loadFactor);  HMapKF(int initialCapacity); @SuppressWarnings("unchecked")  HMapKF();  HMapKF(MapKF<? extends K> m); int size(); boolean isEmpty(); float get(K key); boolean containsKey(K key); float put(K key, float value); void putAll(MapKF<? extends K> m); float remove(K key); void clear(); boolean containsValue(float value); @SuppressWarnings("unchecked") Object clone(); Set<K> keySet(); Collection<Float> values(); Set<MapKF.Entry<K>> entrySet(); String toString(); @Override void plus(MapKF<K> m); @Override double dot(MapKF<K> m); @Override void increment(K key); @Override void increment(K key, float value); float length(); void normalize(); @SuppressWarnings("unchecked") MapKF.Entry<K>[] getEntriesSortedByValue(); MapKF.Entry<K>[] getEntriesSortedByValue(int n);  }### Answer:
@Test public void testPlus() throws IOException { HMapKF<Text> m1 = new HMapKF<Text>(); m1.put(new Text("hi"), 5.0f); m1.put(new Text("there"), 22.0f); HMapKF<Text> m2 = new HMapKF<Text>(); m2.put(new Text("hi"), 4.0f); m2.put(new Text("test"), 5.0f); m1.plus(m2); assertEquals(m1.size(), 3); assertTrue(m1.get(new Text("hi")) == 9); assertTrue(m1.get(new Text("there")) == 22); assertTrue(m1.get(new Text("test")) == 5); }