DefaultMapEntry implements Map.Entry<K, V> { @Override public String toString() { return getKey() + "=" + getValue(); } DefaultMapEntry(K key, V value); K getKey(); V getValue(); V setValue(V value); @Override boolean equals(Object o); @Override int hashCode(); @Override String toString();  }
@Test public void toString_() { assertEquals(entry1.toString(), new DefaultMapEntry<String, Object>(null, null).toString()); assertEquals(entry2.toString(), new DefaultMapEntry<String, Object>("hello", "baobao").toString()); }