集合框架_HashSet集合的add()方法的源码

来源：互联网发布：服务器端口打不开编辑：程序博客网时间：2024/05/16 10:16
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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