java数据结构之HashSet和TreeSet

public class HashSet<E>
    extends AbstractSet<E>
    implements Set<E>, Cloneable, java.io.Serializable
{
    static final long serialVersionUID = -5024744406713321676L;

    //HashSet底层是HashMap
    private transient HashMap<E,Object> map;

    // 用来在HashMap中所有的key对应的value值指向这个对象
    private static final Object PRESENT = new Object();

    /**
     * 创建空的HashSet,实际上是创建了一个默认实现的HashMap
     */
    public HashSet() {
        map = new HashMap<>();
    }

    /**
     * 利用集合创建HashSet
     */
    public HashSet(Collection<? extends E> c) {
        map = new HashMap<>(Math.max((int) (c.size()/.75f) + 1, 16));
        addAll(c);
    }

    /**
     * 手动指定容量和加载因子创建HashSet
     */
    public HashSet(int initialCapacity, float loadFactor) {
        map = new HashMap<>(initialCapacity, loadFactor);
    }

    /**
     * 创建指定容量的HashSet
     */
    public HashSet(int initialCapacity) {
        map = new HashMap<>(initialCapacity);
    }

    /**
     * 底层是LinkedHashSet
     */
    HashSet(int initialCapacity, float loadFactor, boolean dummy) {
        map = new LinkedHashMap<>(initialCapacity, loadFactor);
    }

    /**
     * 获取迭代器
     */
    public Iterator<E> iterator() {
        return map.keySet().iterator();
    }

    /**
     * 获取元素数量
     */
    public int size() {
        return map.size();
    }

    /**
     * 判断是否为空
     */
    public boolean isEmpty() {
        return map.isEmpty();
    }

    /**
     * 判断HashSet是否存在该 对象
     */
    public boolean contains(Object o) {
        return map.containsKey(o);
    }

    /**
     * 新增一个元素，这个元素在HashMap中作为Key，而value则是一个公共的Object
     */
    public boolean add(E e) {
        return map.put(e, PRESENT)==null;
    }

    /**
     * 删除一个元素
     */
    public boolean remove(Object o) {
        return map.remove(o)==PRESENT;
    }

    /**
     * 清空整个集合
     */
    public void clear() {
        map.clear();
    }

    /**
     * 浅克隆
     */
    @SuppressWarnings("unchecked")
    public Object clone() {
        try {
            HashSet<E> newSet = (HashSet<E>) super.clone();
            newSet.map = (HashMap<E, Object>) map.clone();
            return newSet;
        } catch (CloneNotSupportedException e) {
            throw new InternalError(e);
        }
    }

    /**
     * 将HashSet写入流中
     */
    private void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException {
        // Write out any hidden serialization magic
        s.defaultWriteObject();

        // Write out HashMap capacity and load factor
        s.writeInt(map.capacity());
        s.writeFloat(map.loadFactor());

        // Write out size
        s.writeInt(map.size());

        // Write out all elements in the proper order.
        for (E e : map.keySet())
            s.writeObject(e);
    }

    /**
     * 从流中读取HashSet的元素
     */
    private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        // Read in any hidden serialization magic
        s.defaultReadObject();

        // Read capacity and verify non-negative.
        int capacity = s.readInt();
        if (capacity < 0) {
            throw new InvalidObjectException("Illegal capacity: " +
                                             capacity);
        }

        // Read load factor and verify positive and non NaN.
        float loadFactor = s.readFloat();
        if (loadFactor <= 0 || Float.isNaN(loadFactor)) {
            throw new InvalidObjectException("Illegal load factor: " +
                                             loadFactor);
        }

        // Read size and verify non-negative.
        int size = s.readInt();
        if (size < 0) {
            throw new InvalidObjectException("Illegal size: " +
                                             size);
        }

        // Set the capacity according to the size and load factor ensuring that
        // the HashMap is at least 25% full but clamping to maximum capacity.
        capacity = (int) Math.min(size * Math.min(1 / loadFactor, 4.0f),
                HashMap.MAXIMUM_CAPACITY);

        // Create backing HashMap
        map = (((HashSet<?>)this) instanceof LinkedHashSet ?
               new LinkedHashMap<E,Object>(capacity, loadFactor) :
               new HashMap<E,Object>(capacity, loadFactor));

        // Read in all elements in the proper order.
        for (int i=0; i<size; i++) {
            @SuppressWarnings("unchecked")
                E e = (E) s.readObject();
            map.put(e, PRESENT);
        }
    }

    /**
     * 分割迭代器
     */
    public Spliterator<E> spliterator() {
        return new HashMap.KeySpliterator<E,Object>(map, 0, -1, 0, 0);
    }
}

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();
    
    /**
     * Constructs a set backed by the specified navigable map.
     */
    TreeSet(NavigableMap<E,Object> m) {
        this.m = m;
    }
    
    public TreeSet() {
        this(new TreeMap<E,Object>());
    }
    
    /**
     * 传入比较器
     */
    public TreeSet(Comparator<? super E> comparator) {
        this(new TreeMap<>(comparator));
    }
    
    /**
     * 通过集合创建TreeSet，按照元素的自然排序
     */
    public TreeSet(Collection<? extends E> c) {
        this();
        addAll(c);
    }
    
    /**
     * 通过SortedSet的实现类来创建TreeSet，指定比较器为SortedSet实现类的比较器
     */
    public TreeSet(SortedSet<E> s) {
        this(s.comparator());
        addAll(s);
    }
    
    /**
     * 返回迭代器
     */
    public Iterator<E> iterator() {
        return m.navigableKeySet().iterator();
    }
    
    /**
     * 返回逆序迭代器
     */
    public Iterator<E> descendingIterator() {
        return m.descendingKeySet().iterator();
    }
    
    /**
     * 逆序视图
     */
    public NavigableSet<E> descendingSet() {
        return new TreeSet<>(m.descendingMap());
    }
    
    /**
     * 元素个数
     */
    public int size() {
        return m.size();
    }
    
    /**
     * 集合是否为空
     */
    public boolean isEmpty() {
        return m.isEmpty();
    }
    
    /**
     * TreeSet是否包含元素o
     */
    public boolean contains(Object o) {
        return m.containsKey(o);
    }
    
    /**
     * 添加元素
     */
    public boolean add(E e) {
        return m.put(e, PRESENT)==null;
    }
    
    /**
     * 删除元素
     */
    public boolean remove(Object o) {
        return m.remove(o)==PRESENT;
    }
    
    /**
     * 清空集合
     */
    public void clear() {
        m.clear();
    }
    
    /**
     * 批量添加元素
     */
    public  boolean addAll(Collection<? extends E> c) {
        // Use linear-time version if applicable
        if (m.size()==0 && c.size() > 0 &&
            c instanceof SortedSet &&
            m instanceof TreeMap) {
            SortedSet<? extends E> set = (SortedSet<? extends E>) c;
            TreeMap<E,Object> map = (TreeMap<E, Object>) m;
            Comparator<?> cc = set.comparator();
            Comparator<? super E> mc = map.comparator();
            if (cc==mc || (cc != null && cc.equals(mc))) {
                map.addAllForTreeSet(set, PRESENT);
                return true;
            }
        }
        return super.addAll(c);
    }
    
    /**
     * 返回视图
     */
    public NavigableSet<E> subSet(E fromElement, boolean fromInclusive,
                                  E toElement,   boolean toInclusive) {
        return new TreeSet<>(m.subMap(fromElement, fromInclusive,
                                       toElement,   toInclusive));
    }
    
    /**
     * 返回小于toElement的元素视图，inclusive为true可以等于toElement
     */
    public NavigableSet<E> headSet(E toElement, boolean inclusive) {
        return new TreeSet<>(m.headMap(toElement, inclusive));
    }
    
    /**
     * 返回大于fromElement的元素视图,inclusive为true可以等于fromElement
     */
    public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
        return new TreeSet<>(m.tailMap(fromElement, inclusive));
    }
    
    /**
     * 返回fromElement，toElement中间的 视图
     */
    public SortedSet<E> subSet(E fromElement, E toElement) {
        return subSet(fromElement, true, toElement, false);
    }
    
    /**
     * 返回小于toElement的视图
     */
    public SortedSet<E> headSet(E toElement) {
        return headSet(toElement, false);
    }
    
    /**
     * 返回大于fromElement的元素视图
     */
    public SortedSet<E> tailSet(E fromElement) {
        return tailSet(fromElement, true);
    }
    //获取比较器
    public Comparator<? super E> comparator() {
        return m.comparator();
    }
    //返回第一个元素
    public E first() {
        return m.firstKey();
    }
    //返回最后一个元素
    public E last() {
        return m.lastKey();
    }
    
    // NavigableSet API methods
    
    /**
     * 返回小于e的最大的元素，没有就返回null
     */
    public E lower(E e) {
        return m.lowerKey(e);
    }
    
    /**
     * 返回小于或等于e的最大元素，没有返回null
     */
    public E floor(E e) {
        return m.floorKey(e);
    }
    
    /**
     * 返回大于等于e的最小元素
     */
    public E ceiling(E e) {
        return m.ceilingKey(e);
    }
    
    /**
     * 返回大于e的最小元素
     */
    public E higher(E e) {
        return m.higherKey(e);
    }
    
    /**
     * 返回并删除第一个元素
     */
    public E pollFirst() {
        Map.Entry<E,?> e = m.pollFirstEntry();
        return (e == null) ? null : e.getKey();
    }
    
    /**
     * 返回并删除最后一个元素
     */
    public E pollLast() {
        Map.Entry<E,?> e = m.pollLastEntry();
        return (e == null) ? null : e.getKey();
    }
    
    
    
    private static final long serialVersionUID = -2479143000061671589L;
}