public class HashMap<K,V>
{static final int DEFAULT_INITIAL_CAPACITY = 16 ; // 默认初始容量是16。（必须是2的次方）static final int MAXIMUM_CAPACITY = 1 << 30 ; // 即2的30次方static final float DEFAULT_LOAD_FACTOR = 0.75f; // 默认装载因子Entry[] table;  // Entry表int size; // Entry[]实际存储的Entry个数int threshold; // reash的阈值，=capacity * load factorfinal float loadFactor;// 构造函数public HashMap(int initialCapacity, float loadFactor) {// 找到一个比initialCapacity大的最小的2的次方数int capacity = 1;while (capacity < initialCapacity)capacity <<= 1;}this.loadFactor = loadFactor;threshold = (int)(capacity * loadFactor);table = new Entry[capacity];// addEntry()void addEntry(int hash, K key, V value, int bucketIndex) {Entry<K,V> e = table[bucketIndex];table[bucketIndex] = new Entry<>(hash, key, value, e);if (size++ >= threshold)resize(2 * table.length);}// put()：添加元素public V put(K key, V value) {int hash = hash(key.hashCode());     // key的hash值int i = indexFor(hash,table.length);     // 槽位// 寻找是否已经有key存在，如果已经存在，使用新值覆盖旧值，返回旧值for (Entry<K,V> e = table[i]; e != null; e = e.next) {Object k;if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {V oldValue = e.value;e.value = value;return oldValue;}}// 添加EntryaddEntry(hash,key,value,i);return null;}// resize()：重新哈希void resize(int newCapacity) {Entry[] oldTable = table;int oldCapacity = oldTable.length;Entry[] newTable = new Entry[newCapacity];transfer(newTable);table = newTable;threshold = (int)(newCapacity * loadFactor);}/*** Transfers all entries from current table to newTable.*/void transfer(Entry[] newTable) {Entry[] src = table;int newCapacity = newTable.length;for (int j = 0; j < src.length; j++) {Entry<K,V> e = src[j];if (e != null) {src[j] = null;     do {Entry<K,V> next = e.next;int i = indexFor(e.hash, newCapacity);e.next = newTable[i];newTable[i] = e;e = next;} while (e != null);}}}}