TreeSet

TreeSet——底层是TreeMap

package java.util;

public class TreeSet<E> extends AbstractSet<E>
    implements NavigableSet<E>, Cloneable, java.io.Serializable {

    private transient NavigableMap<E,Object> m;

    private static final Object PRESENT = new Object();

    TreeSet(NavigableMap<E,Object> m) {
        this.m = m;
    }

    public TreeSet() {
        this(new TreeMap<E,Object>());
    }

    public TreeSet(Comparator<? super E> comparator) {
        this(new TreeMap<>(comparator));
    }

    public TreeSet(Collection<? extends E> c) {
        this();
        addAll(c);
    }

    public TreeSet(SortedSet<E> s) {
        this(s.comparator());
        addAll(s);
    }
}