Vector和Hashtable源碼閱讀與理解

Vector是線程安全的ArrayList:

public synchronized void insertElementAt(E obj, int index) {
        modCount++;
        if (index > elementCount) {
            throw new ArrayIndexOutOfBoundsException(index
                                                     + " > " + elementCount);
        }
        ensureCapacityHelper(elementCount + 1);
        System.arraycopy(elementData, index, elementData, index + 1, elementCount - index);
        elementData[index] = obj;
        elementCount++;
}

Hashtable是線程安全HashMap:

public synchronized V put(K key, V value) {
        if (value == null) {
            throw new NullPointerException();
        }
        Entry<?,?> tab[] = table;
        int hash = key.hashCode();
        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;
}

原理就是在方法級別上鎖，對於高併發的支持並不是很好。所以有了J.U.C包下的ConcurrentHashMap閱讀與理解來支持多線程下HashMap的高併發操作。而多線程下的隊列操作由J.U.C下的ArrayBlockingQueue閱讀與理解來處理。