一文搞定ArrayList、LinkedList、HashMap、HashSet —–源码解读之HashSet

总结 HashSet：

源码：

public class HashSet<E> extends AbstractSet<E> implements Set<E>, Cloneable, java.io.Serializable { 
    @java.io.Serial static final long serialVersionUID = -L; // 序列化版本号 private transient HashMap<E,Object> map; // 底层采用HashMap进行存储 private static final Object PRESENT = new Object(); // 作为HashMap中的value常量，而key则是真正set要存的数据 public HashSet() { 
    map = new HashMap<>(); // 直接创建一个HashMap } public HashSet(Collection<? extends E> c) { 
    // 传入一个集合 map = new HashMap<>(Math.max((int) (c.size()/.75f) + 1, 16)); // 创建一个带初始容量的HashMap addAll(c); // 将集合c中的元素添加进map中 } public HashSet(int initialCapacity, float loadFactor) { 
    map = new HashMap<>(initialCapacity, loadFactor); // 带初始容量和扩容因子的map } public HashSet(int initialCapacity) { 
    map = new HashMap<>(initialCapacity); // 带初始容量的map } HashSet(int initialCapacity, float loadFactor, boolean dummy) { 
    // 只在内部使用的构造方法，创建一个LinkedHashMap map = new LinkedHashMap<>(initialCapacity, loadFactor); } public Iterator<E> iterator() { 
    return map.keySet().iterator(); } public int size() { 
    return map.size(); //返回map存有多少个元素 } public boolean isEmpty() { 
    return map.isEmpty(); // 判断map是否为空 } public boolean contains(Object o) { 
    return map.containsKey(o); // 判断o是否在map中 } public boolean add(E e) { 
    return map.put(e, PRESENT)==null;// 添加元素，将数据作为key } public boolean remove(Object o) { 
    return map.remove(o)==PRESENT; // 移除元素 } public void clear() { 
    map.clear(); // 清空map } @SuppressWarnings("unchecked") public Object clone() { 
    try { 
    HashSet<E> newSet = (HashSet<E>) super.clone(); // 拷贝HashSet newSet.map = (HashMap<E, Object>) map.clone(); // 拷贝map将map赋值给上面拷贝的HashSet中 return newSet; // 返回set } catch (CloneNotSupportedException e) { 
    throw new InternalError(e); } } // 序列化 @java.io.Serial 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); } // 反序列化 @java.io.Serial 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.getJavaObjectInputStreamAccess().checkArray(s, Map.Entry[].class, HashMap.tableSizeFor(capacity)); map = (((HashSet<?>)this) instanceof LinkedHashSet ? new LinkedHashMap<>(capacity, loadFactor) : new HashMap<>(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<>(map, 0, -1, 0, 0); // 获取key的迭代器 } @Override public Object[] toArray() { 
    return map.keysToArray(new Object[map.size()]); // map的key转换为数组 } @Override public <T> T[] toArray(T[] a) { 
    return map.keysToArray(map.prepareArray(a)); // 带泛型的转换key为数组 } }