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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