一、类图
二、要点
1. TreeSet 是基于 TreeMap 实现的，内置了 NavigableMap，构造函数直接使用 TreeMap
/**
* The backing map.
*/
private transient NavigableMap<E,Object> m;
/**
* Constructs a new, empty tree set, sorted according to the
* natural ordering of its elements. All elements inserted into
* the set must implement the {@link Comparable} interface.
* Furthermore, all such elements must be <i>mutually
* comparable</i>: {@code e1.compareTo(e2)} must not throw a
* {@code ClassCastException} for any elements {@code e1} and
* {@code e2} in the set. If the user attempts to add an element
* to the set that violates this constraint (for example, the user
* attempts to add a string element to a set whose elements are
* integers), the {@code add} call will throw a
* {@code ClassCastException}.
*/
public TreeSet() {
this(new TreeMap<E,Object>());
}/**
* Constructs a new, empty tree set, sorted according to the specified
* comparator. All elements inserted into the set must be <i>mutually
* comparable</i> by the specified comparator: {@code comparator.compare(e1,
* e2)} must not throw a {@code ClassCastException} for any elements
* {@code e1} and {@code e2} in the set. If the user attempts to add
* an element to the set that violates this constraint, the
* {@code add} call will throw a {@code ClassCastException}.
*
* @param comparator the comparator that will be used to order this set.
* If {@code null}, the {@linkplain Comparable natural
* ordering} of the elements will be used.
*/
public TreeSet(Comparator<? super E> comparator) {
this(new TreeMap<>(comparator));
}
2. TreeSet 提供逆序迭代 descendingSet
3. TreeSet 内部实现都是委托给 TreeMap 实现了
public boolean contains(Object o) {
return m.containsKey(o);
}
4. HashSet 是基于 HashMap 实现的
public HashSet() {
map = new HashMap<>();
}
5. LinkedHashSet 基于 HashMap 的子类 LinkedHashMap 实现
public LinkedHashSet(int initialCapacity, float loadFactor) {
super(initialCapacity, loadFactor, true);
}// super method
HashSet(int initialCapacity, float loadFactor, boolean dummy) {
map = new LinkedHashMap<>(initialCapacity, loadFactor);
}