原文链 id="hashset详解">HashSet详解
HashSet是基于HashMap实现的一个单列存储的集合类，将所有的数据存在HashMap的key值中，而value全部使用一个Object对象存储
继承关系
public class HashSet<E> extends AbstractSet<E> implements Set<E>, Cloneable, java.io.Serializable
继承了AbstractSet类，实现了Set接口、Cloneable接口和Serializable接口，所以HashSet是支持克隆和序列化的
源码分析
关键变量
// 使用HashMap存储数据 map的key为HashSet的元素值private transient HashMap<E,Object> map;// Dummy value to associate with an Object in the backing Map// map中所有的值都是该Object对象private static final Object PRESENT = new Object();构造器
// 无参构造器，直接实例化一个HashMappublic HashSet() { map = new HashMap<>();}/** * 使用的是HahMap中传入初始容量的构造器 */public HashSet(Collection<? extends E> c) { map = new HashMap<>(Math.max((int) (c.size()/.75f) + 1, 16)); addAll(c);}/** * 使用的是HahMap中传入初始容量和加载因子的构造器 */public HashSet(int initialCapacity, float loadFactor) { map = new HashMap<>(initialCapacity, loadFactor);}/** * 使用的是HahMap中传入初始容量的构造器 */public HashSet(int initialCapacity) { map = new HashMap<>(initialCapacity);}/** * 该构造器是提供给LinkedHashSet使用的，不对外暴露，实例化的是LinkedHashMap */HashSet(int initialCapacity, float loadFactor, boolean dummy) { map = new LinkedHashMap<>(initialCapacity, loadFactor);}方法分析
HashSet的方法实现都非常简单，直接使用封装的HashMap来操作数据，真正执行的是HashMap的方法
/** * Returns an iterator over the elements in this set. The elements * are returned in no particular order. * * @return an Iterator over the elements in this set * @see ConcurrentModificationException */public Iterator<E> iterator() { return map.keySet().iterator();}/** * Returns the number of elements in this set (its cardinality). * * @return the number of elements in this set (its cardinality) */public int size() { return map.size();}/** * Returns <tt>true</tt> if this set contains no elements. * * @return <tt>true</tt> if this set contains no elements */public boolean isEmpty() { return map.isEmpty();}/** * Returns <tt>true</tt> if this set contains the specified element. * More formally, returns <tt>true</tt> if and only if this set * contains an element <tt>e</tt> such that * <tt>(o==null ? e==null : o.equals(e))</tt>. * * @param o element whose presence in this set is to be tested * @return <tt>true</tt> if this set contains the specified element */public boolean contains(Object o) { return map.containsKey(o);}/** * Adds the specified element to this set if it is not already present. * More formally, adds the specified element <tt>e</tt> to this set if * this set contains no element <tt>e2</tt> such that * <tt>(e==null ? e2==null : e.equals(e2))</tt>. * If this set already contains the element, the call leaves the set * unchanged and returns <tt>false</tt>. * * @param e element to be added to this set * @return <tt>true</tt> if this set did not already contain the specified * element */public boolean add(E e) { return map.put(e, PRESENT)==null;}/** * Removes the specified element from this set if it is present. * More formally, removes an element <tt>e</tt> such that * <tt>(o==null ? e==null : o.equals(e))</tt>, * if this set contains such an element. Returns <tt>true</tt> if * this set contained the element (or equivalently, if this set * changed as a result of the call). (This set will not contain the * element once the call returns.) * * @param o object to be removed from this set, if present * @return <tt>true</tt> if the set contained the specified element */public boolean remove(Object o) { return map.remove(o)==PRESENT;}/** * Removes all of the elements from this set. * The set will be empty after this call returns. */public void clear() { map.clear();}由于本身的博客百度没有收录，博客地 />
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原文链id="hashset详解">HashSet详解HashSet是基于HashMap实现的一个单列存储的集合类，将所有的数据存在HashMap的key值中，而value全部使用一个Object对象存储继承关系publicclassHashSet<E>extendsAbstractSet<E>implementsSet<E>,Clon
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