### Question:
Constructor implements TreeConstructor<E, MutableSettableNode<E>, MutableTreeImpl<E>> { @Override public Class<? extends Tree> forClass() { return MutableTreeImpl.class; }  @SafeVarargs @Override final MutableTreeImpl<E> build(E e, MutableTreeImpl<E>... subtrees); @Override Class<? extends Tree> forClass();  }### Answer:
@Test public void key() { final Constructor<String> constructor = new Constructor<>(); assertEquals(MutableTreeImpl.class, constructor.forClass()); }