ArrayList源码：

private static final int DEFAULT_CAPACITY = 10;//默认长度    /**     * Shared empty array instance used for empty instances.     */    private static final Object[] EMPTY_ELEMENTDATA = {}; //默认数组    /**     * The array buffer into which the elements of the ArrayList are stored.     * The capacity of the ArrayList is the length of this array buffer. Any     * empty ArrayList with elementData == EMPTY_ELEMENTDATA will be expanded to     * DEFAULT_CAPACITY when the first element is added.     */    private transient Object[] elementData; //存放数据的数组    /**     * The size of the ArrayList (the number of elements it contains).     *     * @serial     */    private int size;            /**     * Constructs an empty list with an initial capacity of ten.     */    public ArrayList() {        super();        this.elementData = EMPTY_ELEMENTDATA;    }        public boolean add(E e) {        ensureCapacityInternal(size + 1);  // Increments modCount!!        elementData[size++] = e;        return true;    }         private void ensureCapacityInternal(int minCapacity) {        if (elementData == EMPTY_ELEMENTDATA) {            minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);        }        //判断添加的第几个元素是否比数组长度大，是的话扩容        ensureExplicitCapacity(minCapacity);    }         private void ensureExplicitCapacity(int minCapacity) {        modCount++;        // overflow-conscious code          if (minCapacity - elementData.length > 0)            grow(minCapacity);    }        private void grow(int minCapacity) {        // overflow-conscious code        int oldCapacity = elementData.length;        int newCapacity = oldCapacity + (oldCapacity >> 1);//扩容两倍        if (newCapacity - minCapacity < 0)            newCapacity = minCapacity;        if (newCapacity - MAX_ARRAY_SIZE > 0)            newCapacity = hugeCapacity(minCapacity);        // minCapacity is usually close to size, so this is a win:        elementData = Arrays.copyOf(elementData, newCapacity);    }

 

LinkedList源码：

public boolean add(E e) {        linkLast(e);        return true;    }        void linkLast(E e) {        final Node
     
       l = last;        final Node
      
        newNode = new Node<>(l, e, null);        last = newNode;//需要添加的节点记作上一个节点，供下次使用。        if (l == null)            first = newNode;//第一个添加进来的作为第一个节点        else            l.next = newNode;//记住下一个节点        size++;        modCount++;    }
      
     

LinkedList还有linkBefore、linkFirst...等等其他方法。

 

Vector源码：

public Vector(int initialCapacity, int capacityIncrement) {        super();        if (initialCapacity < 0)            throw new IllegalArgumentException("Illegal Capacity: "+                                               initialCapacity);        this.elementData = new Object[initialCapacity];        this.capacityIncrement = capacityIncrement;    }    public Vector(int initialCapacity) {        this(initialCapacity, 0);    }    public Vector() {        this(10);    }

Vector的三个构造函数

 

//同步方法    public synchronized boolean add(E e) {        modCount++;        ensureCapacityHelper(elementCount + 1);        elementData[elementCount++] = e;        return true;    }        private void ensureCapacityHelper(int minCapacity) {        // overflow-conscious code        //判断是否需要扩容        if (minCapacity - elementData.length > 0)            grow(minCapacity);    }        private void grow(int minCapacity) {        // overflow-conscious code        int oldCapacity = elementData.length;        int newCapacity = oldCapacity + ((capacityIncrement > 0) ?                                         capacityIncrement : oldCapacity);//扩原来的一倍或者是设置扩容步长，每次增加步长长度。        if (newCapacity - minCapacity < 0)            newCapacity = minCapacity;        if (newCapacity - MAX_ARRAY_SIZE > 0)            newCapacity = hugeCapacity(minCapacity);        elementData = Arrays.copyOf(elementData, newCapacity);    }

list和set的toString方法是在AbstractCollection类重写了。

 

总结：LinkedList插入快，查询慢，ArrayList查询快，插入慢，扩容长度为原来的一半，可以给定数组长度。Vector可以给定长度和扩容步长。没有给定步长，扩容一倍，给定了，每次增加步长。