Java集合深入学习 - HashSet源码解析（基于jdk1.8）

HashSet。。。感觉就像是一个阉割版的HashMap。。

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

    /** HashMap-- */
    private transient HashMap<E,Object> map;

    private static final Object PRESENT = new Object();

    /**
     * 构造方法  初始化map
     */
    public HashSet() {
        map = new HashMap<>();
    }

    /**
     * 传入集合  根据集合大小初始化HashMap
     */
    public HashSet(Collection<? extends E> c) {
        map = new HashMap<>(Math.max((int) (c.size()/.75f) + 1, 16));
        addAll(c);
    }
    public HashSet(int initialCapacity, float loadFactor) {
        map = new HashMap<>(initialCapacity, loadFactor);
    }
    public HashSet(int initialCapacity) {
        map = new HashMap<>(initialCapacity);
    }
    HashSet(int initialCapacity, float loadFactor, boolean dummy) {
        map = new LinkedHashMap<>(initialCapacity, loadFactor);
    }
    
    /**
     * 调用map方法。。。
     */
    public Iterator<E> iterator() {
        return map.keySet().iterator();
    }
    /**
     * 调用map方法。。。
     */
    public int size() {
        return map.size();
    }
    public boolean isEmpty() {
        return map.isEmpty();
    }
    public boolean contains(Object o) {
        return map.containsKey(o);
    }
    public boolean add(E e) {
        return map.put(e, PRESENT)==null;	//map添加数据  value同一为PRESENT
    }
    public boolean remove(Object o) {
        return map.remove(o)==PRESENT;
    }
    public void clear() {
        map.clear();
    }
    @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);
        }
    }
    /** 数据写入ObjectOutputStreams */
    private void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException {
        s.defaultWriteObject();
        s.writeInt(map.capacity());
        s.writeFloat(map.loadFactor());
        s.writeInt(map.size());
        for (E e : map.keySet())
            s.writeObject(e);
    }
    /** 数据读取 从 ObjectInputStream中*/
    private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        s.defaultReadObject();
        int capacity = s.readInt();
        if (capacity < 0) {
            throw new InvalidObjectException("Illegal capacity: " +
                                             capacity);
        }
        float loadFactor = s.readFloat();
        if (loadFactor <= 0 || Float.isNaN(loadFactor)) {
            throw new InvalidObjectException("Illegal load factor: " +
                                             loadFactor);
        }
        int size = s.readInt();
        if (size < 0) {
            throw new InvalidObjectException("Illegal size: " +
                                             size);
        }
        capacity = (int) Math.min(size * Math.min(1 / loadFactor, 4.0f),
                HashMap.MAXIMUM_CAPACITY);
        SharedSecrets.getJavaOISAccess()
                     .checkArray(s, Map.Entry[].class, HashMap.tableSizeFor(capacity));
        map = (((HashSet<?>)this) instanceof LinkedHashSet ?
               new LinkedHashMap<E,Object>(capacity, loadFactor) :
               new HashMap<E,Object>(capacity, loadFactor));
        for (int i=0; i<size; i++) {
            @SuppressWarnings("unchecked")
                E e = (E) s.readObject();
            map.put(e, PRESENT);
        }
    }
    public Spliterator<E> spliterator() {
        return new HashMap.KeySpliterator<E,Object>(map, 0, -1, 0, 0);
    }
}