HashSet 源碼級淺析：哈希去重、無序性驗證與性能特徵

HashSet 源碼級淺析：哈希去重、無序性驗證與性能特徵

核心特性速覽

關鍵源碼片段

public class HashSet extends AbstractSet implements Set, Cloneable, Serializable {
    private transient HashMap map;
    private static final Object PRESENT = new Object();
    
    public HashSet() { map = new HashMap<>(); }
    
    public boolean add(E e) { return map.put(e, PRESENT) == null; }
    public boolean contains(Object o) { return map.containsKey(o); }
    public boolean remove(Object o) { return map.remove(o) == PRESENT; }
    public Iterator iterator() { return map.keySet().iterator(); }
    // ...
}

實戰驗證：去重與無序

1. 元素不可重複

Set