### Question:
Int2FloatOpenHashMapWritable extends Int2FloatOpenHashMap implements Writable { public void plus(Int2FloatOpenHashMapWritable m) { for (Int2FloatMap.Entry e : m.int2FloatEntrySet()) { int key = e.getKey(); float value = e.getValue(); if (this.containsKey(key)) { this.put(key, this.get(key) + value); } else { this.put(key, value); } } } Int2FloatOpenHashMapWritable(); @Override void readFields(DataInput in); void decode(); boolean hasBeenDecoded(); @Override void write(DataOutput out); byte[] serialize(); static Int2FloatOpenHashMapWritable create(DataInput in); static Int2FloatOpenHashMapWritable create(byte[] bytes); void plus(Int2FloatOpenHashMapWritable m); int dot(Int2FloatOpenHashMapWritable m); void increment(int key); void increment(int key, float n); static void setLazyDecodeFlag(boolean b); static boolean getLazyDecodeFlag(); int[] getKeys(); float[] getValues(); void lazyplus(Int2FloatOpenHashMapWritable m); Int2FloatMap.Entry[] getEntriesSortedByValue(); Int2FloatMap.Entry[] getEntriesSortedByValue(int k);  }### Answer:
@Test public void testPlus() throws IOException { Int2FloatOpenHashMapWritable m1 = new Int2FloatOpenHashMapWritable(); m1.put(1, 5.0f); m1.put(2, 22.0f); Int2FloatOpenHashMapWritable m2 = new Int2FloatOpenHashMapWritable(); m2.put(1, 4.0f); m2.put(3, 5.0f); m1.plus(m2); assertEquals(3, m1.size(), 3); assertEquals(9.0f, m1.get(1), 10e-6); assertEquals(22.0f, m1.get(2), 10e-6); assertEquals(5.0f, m1.get(3), 10e-6); }