### Question:
LinkedTreeSet extends AbstractSet<E> { @Override public boolean contains(Object o) { return elements.contains(o); } LinkedTreeSet();  LinkedTreeSet(Collection<? extends E> other); @Override boolean add(E e); @Override boolean remove(Object o); @Override boolean removeAll(Collection<?> c); @Override boolean retainAll(Collection<?> c); @Override void clear(); @Override boolean contains(Object o); @Override Iterator<E> iterator(); @Override int hashCode(); @Override boolean equals(Object o); @Override int size(); @Override String toString();  }### Answer:
@Test void testContains() throws Exception { Set<Object> set1 = new LinkedTreeSet<>(); assertThat(set1.contains(0)).isFalse(); set1.add(-0.0); set1.add(1); assertThat(set1.contains(0)).isTrue(); assertThat(set1.contains(0.0)).isTrue(); assertThat(set1.contains(1.0)).isTrue(); assertThat(set1.contains(1)).isTrue(); assertThat(set1.contains(2)).isFalse(); }