【Java基础】--ArrayList 和 Vector 的区别是什么？？

小灰灰 2021-12-16 09:25 520阅读 0赞

### 1.线程安全 ###

**Vector 使用了 Synchronized 来实现线程同步，是线程安全的，而 ArrayList 是非线程安全的。**

源码分析：

Vector

/**
         * Appends the specified element to the end of this Vector.
         *
         * @param e element to be appended to this Vector
         * @return {@code true} (as specified by {@link Collection#add})
         * @since 1.2
         */
        public synchronized boolean add(E e) {
            modCount++;
            ensureCapacityHelper(elementCount + 1);
            elementData[elementCount++] = e;
            return true;
        }

Arraylist

/**
         * Appends the specified element to the end of this list.
         *
         * @param e element to be appended to this list
         * @return <tt>true</tt> (as specified by {@link Collection#add})
         */
        public boolean add(E e) {
            ensureCapacityInternal(size + 1);  // Increments modCount!!
            elementData[size++] = e;
            return true;
        }

### 2.扩容 ###

**扩容：ArrayList 和 Vector 都会根据实际的需要动态的调整容量，只不过在 Vector 扩容每次会增加 1 倍，而 ArrayList 只会增加 50%。**

Vector

/**
         * The amount by which the capacity of the vector is automatically
         * incremented when its size becomes greater than its capacity.  If
         * the capacity increment is less than or equal to zero, the capacity
         * of the vector is doubled each time it needs to grow.
         *
         * @serial
         */
        protected int capacityIncrement;

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Arraylist

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但是在Vector的源码注解中还是说明了一下：

在不考虑并发问题的时候还是推荐使用Arraylist

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