How to use

TreeMap$KeySet

in

java.util

public boolean remove(Object o) {
  int oldSize = size();
  m.remove(o);
  return size() != oldSize;
}
public NavigableSet<E> subSet(E fromElement, boolean fromInclusive,

@Override public Set<K> keySet() {
  KeySet result = keySet;
  return result != null ? result : (keySet = new KeySet());
}

  public NavigableSet<E> descendingSet() {
    return new KeySet(m.descendingMap());
  }
}

public NavigableSet<K> navigableKeySet() {
  KeySet result = keySet;
  return result != null ? result : (keySet = new KeySet());
}

public SortedSet<E> subSet(E fromElement, E toElement) {
  return subSet(fromElement, true, toElement, false);
}
public SortedSet<E> headSet(E toElement) {

@Override public Set<K> keySet() {
  KeySet result = keySet;
  return result != null ? result : (keySet = new KeySet());
}

  public NavigableSet<E> descendingSet() {
    return new KeySet(m.descendingMap());
  }
}

public SortedSet<E> subSet(E fromElement, E toElement) {
  return subSet(fromElement, true, toElement, false);
}
public SortedSet<E> headSet(E toElement) {

public SortedSet<E> tailSet(E fromElement) {
  return tailSet(fromElement, true);
}
public NavigableSet<E> descendingSet() {

@Override public Set<K> keySet() {
  KeySet result = keySet;
  return result != null ? result : (keySet = new KeySet());
}

public NavigableSet<K> navigableKeySet() {
  KeySet result = keySet;
  return result != null ? result : (keySet = new KeySet());
}

@Override public Set<K> keySet() {
  KeySet result = keySet;
  return result != null ? result : (keySet = new KeySet());
}

public NavigableSet<K> navigableKeySet() {
  KeySet result = keySet;
  return result != null ? result : (keySet = new KeySet());
}

public NavigableSet<E> headSet(E toElement, boolean inclusive) {
  return new KeySet<>(m.headMap(toElement, inclusive));
}
public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {

public NavigableSet<K> navigableKeySet() {
  KeySet result = keySet;
  return result != null ? result : (keySet = new KeySet());
}

public NavigableSet<E> subSet(E fromElement, boolean fromInclusive,
               E toElement,   boolean toInclusive) {
  return new KeySet<>(m.subMap(fromElement, fromInclusive,
                 toElement,   toInclusive));
}
public NavigableSet<E> headSet(E toElement, boolean inclusive) {

/**
 * @since 1.6
 */
public NavigableSet<K> navigableKeySet() {
  KeySet<K> nks = navigableKeySet;
  return (nks != null) ? nks : (navigableKeySet = new KeySet(this));
}

@Override public Set<K> keySet() {
  KeySet result = keySet;
  return result != null ? result : (keySet = new KeySet());
}

public final NavigableSet<K> navigableKeySet() {
  KeySet<K> nksv = navigableKeySetView;
  return (nksv != null) ? nksv :
    (navigableKeySetView = new TreeMap.KeySet(this));
}

public NavigableSet<K> navigableKeySet() {
  KeySet result = keySet;
  return result != null ? result : (keySet = new KeySet());
}