### Question:
HMapIF implements MapIF, Cloneable, Serializable { @Override public void plus(MapIF m) { for (MapIF.Entry e : m.entrySet()) { int key = e.getKey(); if (this.containsKey(key)) { this.put(key, this.get(key) + e.getValue()); } else { this.put(key, e.getValue()); } } } HMapIF(int initialCapacity, float loadFactor);  HMapIF(int initialCapacity);  HMapIF();  HMapIF(MapIF m); int size(); boolean isEmpty(); float get(int key); boolean containsKey(int key); float put(int key, float value); void putAll(MapIF m); float remove(int key); void clear(); boolean containsValue(float value); Object clone(); Set<Integer> keySet(); Collection<Float> values(); Set<MapIF.Entry> entrySet(); String toString(); @Override void plus(MapIF m); @Override double dot(MapIF m); @Override void increment(int key); @Override void increment(int key, float value); float length(); void normalize(); MapIF.Entry[] getEntriesSortedByValue(); MapIF.Entry[] getEntriesSortedByValue(int n);  }### Answer:
@Test public void testPlus() throws IOException { HMapIF m1 = new HMapIF(); m1.put(1, 5.0f); m1.put(2, 22.0f); HMapIF m2 = new HMapIF(); m2.put(1, 4.0f); m2.put(3, 5.0f); m1.plus(m2); assertEquals(m1.size(), 3); assertTrue(m1.get(1) == 9); assertTrue(m1.get(2) == 22); assertTrue(m1.get(3) == 5); }