HashTable和Vector爲何逐漸被廢棄

HashTable，不容許鍵值爲null，還一個就是put方法使用sychronized方法進行線程同步，單線程無需同步，多線程可用concurren包的類型。 如編程思想裏面說的做爲工具類，封閉性作的很差沒有一個方法變量是final的，做爲java1.0/1.1時代的容器逐漸被HashMap取代。一樣Vector也有一樣的問題，做爲普通集合類，添加數據的方法也是作了同步，效率受極大影響。

HashTable源碼中的put，鍵和值都不容許爲null 
   /**
     * Maps the specified <code>key</code> to the specified
     * <code>value</code> in this hashtable. Neither the key nor the
     * value can be <code>null</code>. <p>
     *
     * The value can be retrieved by calling the <code>get</code> method
     * with a key that is equal to the original key.
     *
     * @param      key     the hashtable key
     * @param      value   the value
     * @return     the previous value of the specified key in this hashtable,
     *             or <code>null</code> if it did not have one
     * @exception  NullPointerException  if the key or value is
     *               <code>null</code>
     * @see     Object#equals(Object)
     * @see     #get(Object)
     */
    public synchronized V put(K key, V value) {
        // Make sure the value is not null，值爲null報空指針

        if (value == null) {
            throw new NullPointerException();
        }

        // Makes sure the key is not already in the hashtable.
        Entry<?,?> tab[] = table;
        int hash = key.hashCode();//key爲null，沒法計算hashcode也會報空指針
        int index = (hash & 0x7FFFFFFF) % tab.length;
        @SuppressWarnings("unchecked")
        Entry<K,V> entry = (Entry<K,V>)tab[index];
        for(; entry != null ; entry = entry.next) {
            if ((entry.hash == hash) && entry.key.equals(key)) {
                V old = entry.value;
                entry.value = value;
                return old;
            }
        }

        addEntry(hash, key, value, index);
        return null;
    }