java中Hashtable和HashMap的区别分析

 public class Hashtable<K,V>
     extends Dictionary<K,V>
     implements Map<K,V>, Cloneable, java.io.Serializable

public class HashMap<K,V>
    extends AbstractMap<K,V>
     implements Map<K,V>, Cloneable, Serializable

public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m)

Map m = Collections.synchronizedMap(new HashMap());
       ...
   Set s = m.keySet();  // Needn't be in synchronized block
       ...
   synchronized(m) {  // Synchronizing on m, not s!
       Iterator i = s.iterator(); // Must be in synchronized block
       while (i.hasNext())
           foo(i.next());
   }

int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;

public V put(K key, V value) {
         if (key == null)
             return putForNullKey(value);
         int hash = hash(key.hashCode());
         int i = indexFor(hash, table.length);
         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;
                 e.recordAccess(this);
                 return oldValue;
             }
         }

         modCount++;
         addEntry(hash, key, value, i);
         return null;
     }

static int hash(int h) {
         // 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);
     }

   static int indexFor(int h, int length) {
         return h & (length-1);
     }