Java集合-TreeSet

不念不忘少年蓝@ 2022-05-29 06:14 237阅读 0赞

## 介绍 ##

> 1.  TreeSet实现了NavigableSet接口,TreeSet的底层是一个NavigableMap，TreeSet的元素是有序的;
> 2.  TreeSet不允许添加null元素（NullPointerException），不允许添加重复元素，即第二次添加重复元素会失败，add(E e)函数返回false；
> 3.  TreeSet是非线程同步的，是不安全的，可采用如下方法使得TreeSet线程安全：SortedSet s = Collections.synchronizedSortedSet(new TreeSet(…));
> 4.  TreeSet是基于TreeMap实现的，TreeSet的元素支持2种排序方式：自然排序或者根据提供的Comparator进行排序。

## 类图 ##

![TreeSet的接口依赖图][TreeSet]

## 源码 ##

### 继承关系 ###

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

### 成员变量 ###

/** * The backing map. */
    private transient NavigableMap<E,Object> m;
    
    // Dummy value to associate with an Object in the backing Map
    private static final Object PRESENT = new Object();
    
    private static final long serialVersionUID = -2479143000061671589L;

### 构造函数 ###

/** * Constructs a set backed by the specified navigable map. */
    TreeSet(NavigableMap<E,Object> m) {
        this.m = m;
    }
    
    /** * Constructs a new, empty tree set, sorted according to the * natural ordering of its elements. */
    public TreeSet() {
        this(new TreeMap<E,Object>());
    }
    
    /** * Constructs a new, empty tree set, sorted according to the specified * comparator. */
    public TreeSet(Comparator<? super E> comparator) {
        this(new TreeMap<>(comparator));
    }
    
    /** * Constructs a new tree set containing the elements in the specified * collection, sorted according to the <i>natural ordering</i> of its * elements. */
    public TreeSet(Collection<? extends E> c) {
        this();
        addAll(c);
    }
    
    /** * Constructs a new tree set containing the same elements and * using the same ordering as the specified sorted set. */
    public TreeSet(SortedSet<E> s) {
        this(s.comparator());
        addAll(s);
    }

### 常用方法 ###

/** * Returns the number of elements in this set (its cardinality). */
    public int size() {
        return m.size();
    }
    
    /** * Returns {@code true} if this set contains no elements. */
    public boolean isEmpty() {
        return m.isEmpty();
    }
    /** * Returns {@code true} if this set contains the specified element. */
    public boolean contains(Object o) {
        return m.containsKey(o);
    }
    /** * Adds the specified element to this set if it is not already present. */
    public boolean add(E e) {
        return m.put(e, PRESENT)==null;
    }
    
        /** * Removes the specified element from this set if it is present. */
    public boolean remove(Object o) {
        return m.remove(o)==PRESENT;
    }
    
    /** * Removes all of the elements from this set. * The set will be empty after this call returns. */
    public void clear() {
        m.clear();
    }
    
    /** * Returns a shallow copy of this {@code TreeSet} instance. (The elements * themselves are not cloned.) * * @return a shallow copy of this set */
    @SuppressWarnings("unchecked")
    public Object clone() {
        TreeSet<E> clone;
        try {
            clone = (TreeSet<E>) super.clone();
        } catch (CloneNotSupportedException e) {
            throw new InternalError(e);
        }
    
        clone.m = new TreeMap<>(m);
        return clone;
    }

[TreeSet]: