JDK1.8源码阅读之——VECTOR,ARRAYLIST, LINKEDLIST

一、ArrayList

public class ArrayList<E> extends AbstractList<E>        implements List<E>, RandomAccess, Cloneable, java.io.Serializable
   /**     * Default initial capacity.     */    private static final int DEFAULT_CAPACITY = 10;    /**     * Shared empty array instance used for empty instances.     */    private static final Object[] EMPTY_ELEMENTDATA = {};    /**     * Shared empty array instance used for default sized empty instances. We     * distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when     * first element is added.     */    private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};    /**     * 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 == DEFAULTCAPACITY_EMPTY_ELEMENTDATA     * will be expanded to DEFAULT_CAPACITY when the first element is added.     */    transient Object[] elementData; // non-private to simplify nested class access
存储方式为Object数组，默认容量为10

扩容

public boolean add(E e) {        ensureCapacityInternal(size + 1);  // Increments modCount!!        elementData[size++] = e;        return true;    }
ensureCapacityInternal()

private void ensureCapacityInternal(int minCapacity) {        if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {            minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);        }        ensureExplicitCapacity(minCapacity);    }
ensureExplicitCapacity()

private void ensureExplicitCapacity(int minCapacity) {        modCount++;        // overflow-conscious code        if (minCapacity - elementData.length > 0)            grow(minCapacity);    }
当添加容量大于当前容器容量时调用grow()扩容
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
private void grow(int minCapacity) {        // overflow-conscious code        int oldCapacity = elementData.length;        int newCapacity = oldCapacity + (oldCapacity >> 1);        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);    }
1.扩容容量 = 原容量 + 原容量 / 2

2.如果扩容后容量依旧不足则直接使用添加后的容量大小

3.如果扩容后容量大于MAX_ARRAY_SIZE 即 Integer.MAX_VALUE-8 则调用hugeCapacity方法

4.重新生成一个新容量的容器

 private static int hugeCapacity(int minCapacity) {        if (minCapacity < 0) // overflow            throw new OutOfMemoryError();        return (minCapacity > MAX_ARRAY_SIZE) ?            Integer.MAX_VALUE :            MAX_ARRAY_SIZE;    }
接上一步3， 在不溢出的情况下，最大容量为Integer.MAX_VALUE

二、Vector

public class Vector<E>    extends AbstractList<E>    implements List<E>, RandomAccess, Cloneable, java.io.Serializable
public Vector() {    this(10);}
和ArrayList一样，初始容量为10

protected Object[] elementData;
实现方式也是Object数组

public synchronized boolean add(E e) {    modCount++;    ensureCapacityHelper(elementCount + 1);    elementData[elementCount++] = e;    return true;}
所有方法由synchronized修饰

扩容

省略之前的调用方法，直接来看最终实现吧

private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;    private void grow(int minCapacity) {        // overflow-conscious code        int oldCapacity = elementData.length;        int newCapacity = oldCapacity + ((capacityIncrement > 0) ?                                         capacityIncrement : oldCapacity);        if (newCapacity - minCapacity < 0)            newCapacity = minCapacity;        if (newCapacity - MAX_ARRAY_SIZE > 0)            newCapacity = hugeCapacity(minCapacity);        elementData = Arrays.copyOf(elementData, newCapacity);    }    private static int hugeCapacity(int minCapacity) {        if (minCapacity < 0) // overflow            throw new OutOfMemoryError();        return (minCapacity > MAX_ARRAY_SIZE) ?            Integer.MAX_VALUE :            MAX_ARRAY_SIZE;    }
这里有一个capacityIncrement参数，这个参数是在构造Vector时一个选填参数，如果该值大于零，扩容后的容量就是 原容量 + capacityIncrement, 如果没有传入那么扩容容量 = 原容量 * 2

同样的，如果新生成的容量大于MAX_ARRAY_SIZE,容量定为Integer.MAX_VALUE,即最大值

需要注意的是，每次扩容都需要调用一次Arrays.copyOf方法,需要不断的重新实例化数组，所以在使用中最好直接指定容器大小