interface Collection { ... }
interface Set extends Collection { ... }
class HashSet implements Set { private static final Object PRESENT = new Object(); private transient HashMap<E,Object> map; public HashSet() { map = new HashMap<>(); } public boolean add(E e) { //e=hello,world return map.put(e, PRESENT)==null; } }
class HashMap implements Map { public V put(K key, V value) { //key=e=hello,world //看哈希表是否为空,如果空,就开辟空间 if (table == EMPTY_TABLE) { inflateTable(threshold); } //判断对象是否为null if (key == null) return putForNullKey(value); int hash = hash(key); //和对象的hashCode()方法相关 //在哈希表中查找hash值 int i = indexFor(hash, table.length); for (Entry<K,V> e = table[i]; e != null; e = e.next) { //这次的e其实是第一次的world Object k; if (e.hash == hash && ((k = e.key) == key || key.equals(k))) { V oldValue = e.value; e.value = value; e.recordAccess(this); return oldValue; //走这里其实是没有添加元素 } }
modCount++; addEntry(hash, key, value, i); //把元素添加 return null; } transient int hashSeed = 0; final int hash(Object k) { //k=key=e=hello, int h = hashSeed; if (0 != h && k instanceof String) { return sun.misc.Hashing.stringHash32((String) k); }
h ^= k.hashCode(); //这里调用的是对象的hashCode()方法
// This function ensures that hashCodes that differ only by // constant multiples at each bit position have a bounded // number of collisions (approximately 8 at default load factor). h ^= (h >>> 20) ^ (h >>> 12); return h ^ (h >>> 7) ^ (h >>> 4); } }
hs.add("hello"); hs.add("world"); hs.add("java"); hs.add("world");
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