ArrayList

1、开始
public class ArrayList<E> extends AbstractList<E>
        implements List<E>, RandomAccess, Cloneable, java.io.Serializable
继承了抽象类AbstractList，实现了List接口，RandomAccess接口(数据随机存储)，Cloneable接口(可克隆)，Serializable接口(可序列化)

2、属性
    //用于存放元素的数组，不可进行序列化
    private transient Object[] elementData;

    //已经存放的元素的个数
    private int size;

3、构造器

    //指定列表大小
     public ArrayList(int initialCapacity) {
        super();
        if (initialCapacity < 0)
            throw new IllegalArgumentException("Illegal Capacity: " + initialCapacity);
        this.elementData = new Object[initialCapacity];
    }

    //默认列表大小为10
    public ArrayList() {
        this(10);
    }

    //有初始内容的列表
    public ArrayList(Collection<? extends E> c) {
        elementData = c.toArray();
        size = elementData.length;
        // c.toArray might (incorrectly) not return Object[] (see 6260652)
        if (elementData.getClass() != Object[].class)
            elementData = Arrays.copyOf(elementData, size, Object[].class);
    }

 4、方法
1)、添加
    //向列表中添加元素，返回是否添加成功
    public boolean add(E e) {
         //是否扩容
        ensureCapacityInternal(size + 1);  // Increments modCount!!
        elementData[size++] = e;
        return true;
    }

    //向列表中指定的位置添加元素，其他的元素后移
    public void add(int index, E element) {
        //检测下标是否合法，下标范围[0,size]
        rangeCheckForAdd(index);
        //是否扩容
        ensureCapacityInternal(size + 1);  // Increments modCount!!
        System.arraycopy(elementData, index, elementData, index + 1, size - index);
        elementData[index] = element;
        size++;
    }

2)、获取和设置
    //根据下标返回元素
    E elementData(int index) {
        return (E) elementData[index];
    }

    //根据下标获取元素
    public E get(int index) {
        //检测下标是否合法，下标范围[0,size)
        rangeCheck(index);

        return elementData(index);
    }

    //设置列表中指定位置中的元素，并返回该位置的旧数据
    public E set(int index, E element) {
        //检测下标是否合法，下标范围[0,size)
        rangeCheck(index);

        E oldValue = elementData(index);
        elementData[index] = element;
        return oldValue;
    }
3)、删除
    //删除指定位置的元素，并返回要删除的元素
     public E remove(int index) {
         //检测下标是否合法，下标范围[0,size)
        rangeCheck(index);

        modCount++;
        E oldValue = elementData(index);

        int numMoved = size - index - 1;
        if (numMoved > 0)
            System.arraycopy(elementData, index+1, elementData, index, numMoved);
        elementData[--size] = null; // Let gc do its work

        return oldValue;
    }

       //删除指定的元素，返回是否删除成功，分为删除的元素是否为null，之后分别进行遍历删除
    public boolean remove(Object o) {
        if (o == null) {
            for (int index = 0; index < size; index++)
                if (elementData[index] == null) {
                    fastRemove(index);
                    return true;
                }
        } else {
            for (int index = 0; index < size; index++)
                if (o.equals(elementData[index])) {
                    fastRemove(index);
                    return true;
                }
        }
        return false;
    }

    //快速删除
    /*
    * Private remove method that skips bounds checking and does not
    * return the value removed.
    */
    private void fastRemove(int index) {
        //记录更改的次数
        modCount++;
        //需要移动的元素个数
        int numMoved = size - index - 1;
        if (numMoved > 0)
            System.arraycopy(elementData, index+1, elementData, index, numMoved);
        //利于GC
        elementData[--size] = null; // Let gc do its work
    }


4）、扩容检测
    //目标容量与当前容量进行比较，是否进行扩容
    private void ensureCapacityInternal(int minCapacity) {

        //扩容相当于一次更改
        modCount++;
        // overflow-conscious code
        if (minCapacity - elementData.length > 0)
            grow(minCapacity);
    }

    /**
     * The maximum size of array to allocate.
     * Some VMs reserve some header words in an array.
     * Attempts to allocate larger arrays may result in
     * OutOfMemoryError: Requested array size exceeds VM limit
     */
    private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;

    //扩容，在原来的基础上增加0.5，即容量是原来的1.5倍
    private void grow(int minCapacity) {
        // overflow-conscious code
        int oldCapacity = elementData.length;
        int newCapacity = oldCapacity + (oldCapacity >> 1);
        //一般扩容与目标容量进行比较
        if (newCapacity - minCapacity < 0)
            newCapacity = minCapacity;
        //获取最大的容量
        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);
    }

    //获取最大的列表容量
    private static int hugeCapacity(int minCapacity) {
        if (minCapacity < 0) // overflow
            throw new OutOfMemoryError();
        return (minCapacity > MAX_ARRAY_SIZE) ?
            Integer.MAX_VALUE :
            MAX_ARRAY_SIZE;
    }

5)、范围检测
    
    //下标范围[0,size)
     /**
     * Checks if the given index is in range.  If not, throws an appropriate
     * runtime exception.  This method does *not* check if the index is
     * negative: It is always used immediately prior to an array access,
     * which throws an ArrayIndexOutOfBoundsException if index is negative.
     */
    private void rangeCheck(int index) {
        if (index >= size)
            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
    }


    //下标范围[0,size]，用于add(index)与addAll方法
    /**
     * A version of rangeCheck used by add and addAll.
     */
    private void rangeCheckForAdd(int index) {
        if (index > size || index < 0)
            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
    }

    /**
     * Constructs an IndexOutOfBoundsException detail message.
     * Of the many possible refactorings of the error handling code,
     * this "outlining" performs best with both server and client VMs.
     */
    private String outOfBoundsMsg(int index) {
        return "Index: "+index+", Size: "+size;
    }

6）、获取集合间的交集和差集

    //集合差集
     public boolean removeAll(Collection<?> c) {
        return batchRemove(c, false);
    }

    //集合交集
    public boolean retainAll(Collection<?> c) {
        return batchRemove(c, true);
    }

    //集合间的操作
    private boolean batchRemove(Collection<?> c, boolean complement) {
        final Object[] elementData = this.elementData;
        int r = 0, w = 0;
        boolean modified = false;
        try {
            for (; r < size; r++)
                if (c.contains(elementData[r]) == complement)
                    elementData[w++] = elementData[r];
        } finally {
            // Preserve behavioral compatibility with AbstractCollection,
            // even if c.contains() throws.
            if (r != size) {
                System.arraycopy(elementData, r, elementData, w, size - r);
                w += size - r;
            }
            if (w != size) {
                for (int i = w; i < size; i++)
                    elementData[i] = null;
                modCount += size - w;
                size = w;
                modified = true;
            }
        }
        return modified;
    }

7）、将集合添加到列表中
    
    //将集合添加到列表末尾
    public boolean addAll(Collection<? extends E> c) {
        Object[] a = c.toArray();
        int numNew = a.length;
        ensureCapacityInternal(size + numNew);  // Increments modCount
        System.arraycopy(a, 0, elementData, size, numNew);
        size += numNew;
        return numNew != 0;
    }

    //将集合添加到列表中指定的位置
    public boolean addAll(int index, Collection<? extends E> c) {
        rangeCheckForAdd(index);

        Object[] a = c.toArray();
        int numNew = a.length;
        ensureCapacityInternal(size + numNew);  // Increments modCount

        int numMoved = size - index;
        if (numMoved > 0)
            System.arraycopy(elementData, index, elementData, index + numNew,
                             numMoved);

        System.arraycopy(a, 0, elementData, index, numNew);
        size += numNew;
        return numNew != 0;
    }


8）、基础方法

    //获取列表元素个数
    public int size() {
        return size;
    }

    //列表是否为空，即大小是否为0
    public boolean isEmpty() {
        return size == 0;
    }

    //列表是否包含该元素
    public boolean contains(Object o) {
        return indexOf(o) >= 0;
    }

    //查找元素在列表中第一次出现的位置，循环遍历
    public int indexOf(Object o) {
        if (o == null) {
            for (int i = 0; i < size; i++)
                if (elementData[i]==null)
                    return i;
        } else {
            for (int i = 0; i < size; i++)
                if (o.equals(elementData[i]))
                    return i;
        }
        return -1;
    }

    //查找元素在列表中的最后一次出现的位置，倒序遍历
    public int lastIndexOf(Object o) {
        if (o == null) {
            for (int i = size-1; i >= 0; i--)
                if (elementData[i]==null)
                    return i;
        } else {
            for (int i = size-1; i >= 0; i--)
                if (o.equals(elementData[i]))
                    return i;
        }
        return -1;
    }

    //将列表转换为数组
    public Object[] toArray() {
        return Arrays.copyOf(elementData, size);
    }

    //将列表转换给指定的数组
    @SuppressWarnings("unchecked")
    public <T> T[] toArray(T[] a) {
        if (a.length < size)
            // Make a new array of a's runtime type, but my contents:
            return (T[]) Arrays.copyOf(elementData, size, a.getClass());
        System.arraycopy(elementData, 0, a, 0, size);
        if (a.length > size)
            a[size] = null;
        return a;
    }

    //缩减列表中不存在的元素
    public void trimToSize() {
        modCount++;
        int oldCapacity = elementData.length;
        if (size < oldCapacity) {
            elementData = Arrays.copyOf(elementData, size);
        }
    }

9）、迭代器，都支持fail-fast机制，可能会抛出ConcurrentModificationException异常
    //列表迭代器
    public ListIterator<E> listIterator(int index) {
        if (index < 0 || index > size)
            throw new IndexOutOfBoundsException("Index: "+index);
        return new ListItr(index);
    }

    //列表迭代器
    public ListIterator<E> listIterator() {
        return new ListItr(0);
    }

    //迭代器
    public Iterator<E> iterator() {
        return new Itr();
    }

    //迭代器定义
    private class Itr implements Iterator<E> {
        int cursor;       // index of next element to return
        int lastRet = -1; // index of last element returned; -1 if no such
        int expectedModCount = modCount;

        //是否还有元素
        public boolean hasNext() {
            return cursor != size;
        }

        //获取下一个元素
        @SuppressWarnings("unchecked")
        public E next() {
            checkForComodification();
            //当前元素下标
            int i = cursor;
            if (i >= size)
                throw new NoSuchElementException();
            Object[] elementData = ArrayList.this.elementData;
            if (i >= elementData.length)
                throw new ConcurrentModificationException();
            //下一个元素的下标
            cursor = i + 1;
            //指定当前最后一个下标
            return (E) elementData[lastRet = i];
        }

        //删除当前最后一个元素，并指定当前位置的下标
        public void remove() {
            if (lastRet < 0)
                throw new IllegalStateException();
            checkForComodification();

            try {
                //删除元素
                ArrayList.this.remove(lastRet);
                //指定当前下标
                cursor = lastRet;
                lastRet = -1;
                expectedModCount = modCount;
            } catch (IndexOutOfBoundsException ex) {
                throw new ConcurrentModificationException();
            }
        }

        final void checkForComodification() {
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
        }
    }

 //列表迭代器定义
 private class ListItr extends Itr implements ListIterator<E> {
        ListItr(int index) {
            super();
            cursor = index;
        }
        //是否有前一个
        public boolean hasPrevious() {
            return cursor != 0;
        }

        //获取下一个索引
        public int nextIndex() {
            return cursor;
        }

        //获取前一个索引
        public int previousIndex() {
            return cursor - 1;
        }

        //获取前一个元素
        @SuppressWarnings("unchecked")
        public E previous() {
            checkForComodification();
            int i = cursor - 1;
            if (i < 0)
                throw new NoSuchElementException();
            Object[] elementData = ArrayList.this.elementData;
            if (i >= elementData.length)
                throw new ConcurrentModificationException();
            cursor = i;
            return (E) elementData[lastRet = i];
        }

        //设置元素
        public void set(E e) {
            if (lastRet < 0)
                throw new IllegalStateException();
            checkForComodification();

            try {
                ArrayList.this.set(lastRet, e);
            } catch (IndexOutOfBoundsException ex) {
                throw new ConcurrentModificationException();
            }
        }

        //添加元素
        public void add(E e) {
            checkForComodification();

            try {
                int i = cursor;
                ArrayList.this.add(i, e);
                cursor = i + 1;
                lastRet = -1;
                expectedModCount = modCount;
            } catch (IndexOutOfBoundsException ex) {
                throw new ConcurrentModificationException();
            }
        }
    }

 

10）、子列表，更改子列表时，会影响到父列表，但更改父列表时，子列表将抛出异常ConcurrentModificationException
    //获取子列表
    public List<E> subList(int fromIndex, int toIndex) {
        subListRangeCheck(fromIndex, toIndex, size);
        return new SubList(this, 0, fromIndex, toIndex);
    }

    //子列表检测
    static void subListRangeCheck(int fromIndex, int toIndex, int size) {
        if (fromIndex < 0)
            throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
        if (toIndex > size)
            throw new IndexOutOfBoundsException("toIndex = " + toIndex);
        if (fromIndex > toIndex)
            throw new IllegalArgumentException("fromIndex(" + fromIndex +
                                               ") > toIndex(" + toIndex + ")");
    }

    //以下是子列表对象中的方法

    //子列表构造器
    SubList(AbstractList<E> parent,
            int offset, int fromIndex, int toIndex) {
        this.parent = parent;//父列表对象
        this.parentOffset = fromIndex;
        this.offset = offset + fromIndex;
        this.size = toIndex - fromIndex;//子列表大小
        this.modCount = ArrayList.this.modCount;
        //子列表更改记录，必须跟父列表保持同步，否则抛出异常ConcurrentModificationException
    }

    //往指定位置添加元素
    public void add(int index, E e) {
        rangeCheckForAdd(index);
        checkForComodification();
        //往父列表中添加元素后，需要将更改记录同步到子列表中
        parent.add(parentOffset + index, e);
        this.modCount = parent.modCount;
        this.size++;
    }

    //删除指定位置的元素
    public E remove(int index) {
        rangeCheck(index);
        checkForComodification();
        E result = parent.remove(parentOffset + index);
        //往父列表中删除元素后，需要将更改记录同步到子列表中
        this.modCount = parent.modCount;
        this.size--;
        return result;
    }

    //检测子列表与父列表的更改状态是否一致
       private void checkForComodification() {
        if (ArrayList.this.modCount != this.modCount)
            throw new ConcurrentModificationException();
    }

 

ArrayList的遍历方式
1）、根据索引值进行遍历
2）、通过迭代器进行遍历
3）、通过foreach

ArrayList和LinkedList
1）、ArrayList是基于动态数组实现的数据结构，而LinkedList是基于链表实现的数据结构
2）、对于随机访问get和set，ArrayList优于LinkedList，这是由于LinkedList需要移动指针
3）、对于新增和删除操作add和remove，LinkedList比较占优势，这是由于ArrayList需要移动数据

ArrayList和Vector
1）、Vector和ArrayList实现几乎一样，唯一不同的是Vector是同步类(synchronized)，故开销比ArrayList大，访问慢
2）、Vector每次扩容后其大小是原来的2倍，而ArrayList是1.5倍
3）、Vector还有一个子类Stack

 

 

参考资料：

http://www.importnew.com/17440.html

http://anxpp.com/index.php/archives/664/