ArrayList

1、開始
public class ArrayList<E> extends AbstractList<E>
        implements List<E>, RandomAccess, Cloneable, java.io.Serializable
繼承了抽象類AbstractList，實現了List接口，RandomAccess接口(數據隨機存儲)，Cloneable接口(可克隆)，Serializable接口(可序列化)

2、屬性
    //用於存放元素的數組，不可進行序列化
    private transient Object[] elementData;

    //已經存放的元素的個數
    private int size;

3、構造器

    //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];
    }

    //默認列表大小爲10
    public ArrayList() {
        this(10);
    }

    //有初始內容的列表
    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) {
         //是否擴容
        ensureCapacityInternal(size + 1);  // Increments modCount!!
        elementData[size++] = e;
        return true;
    }

    //向列表中指定的位置添加元素，其餘的元素後移
    public void add(int index, E element) {
        //檢測下標是否合法，下標範圍[0,size]
        rangeCheckForAdd(index);
        //是否擴容
        ensureCapacityInternal(size + 1);  // Increments modCount!!
        System.arraycopy(elementData, index, elementData, index + 1, size - index);
        elementData[index] = element;
        size++;
    }

2)、獲取和設置
    //根據下標返回元素
    E elementData(int index) {
        return (E) elementData[index];
    }

    //根據下標獲取元素
    public E get(int index) {
        //檢測下標是否合法，下標範圍[0,size)
        rangeCheck(index);

        return elementData(index);
    }

    //設置列表中指定位置中的元素，並返回該位置的舊數據
    public E set(int index, E element) {
        //檢測下標是否合法，下標範圍[0,size)
        rangeCheck(index);

        E oldValue = elementData(index);
        elementData[index] = element;
        return oldValue;
    }
3)、刪除
    //刪除指定位置的元素，並返回要刪除的元素
     public E remove(int index) {
         //檢測下標是否合法，下標範圍[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;
    }

       //刪除指定的元素，返回是否刪除成功，分爲刪除的元素是否爲null，以後分別進行遍歷刪除
    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;
    }

    //快速刪除
    /*
    * Private remove method that skips bounds checking and does not
    * return the value removed.
    */
    private void fastRemove(int index) {
        //記錄更改的次數
        modCount++;
        //須要移動的元素個數
        int numMoved = size - index - 1;
        if (numMoved > 0)
            System.arraycopy(elementData, index+1, elementData, index, numMoved);
        //利於GC
        elementData[--size] = null; // Let gc do its work
    }


4）、擴容檢測
    //目標容量與當前容量進行比較，是否進行擴容
    private void ensureCapacityInternal(int minCapacity) {

        //擴容至關於一次更改
        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;

    //擴容，在原來的基礎上增長0.5，即容量是原來的1.5倍
    private void grow(int minCapacity) {
        // overflow-conscious code
        int oldCapacity = elementData.length;
        int newCapacity = oldCapacity + (oldCapacity >> 1);
        //通常擴容與目標容量進行比較
        if (newCapacity - minCapacity < 0)
            newCapacity = minCapacity;
        //獲取最大的容量
        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);
    }

    //獲取最大的列表容量
    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)、範圍檢測
    
    //下標範圍[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));
    }


    //下標範圍[0,size]，用於add(index)與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）、獲取集合間的交集和差集

    //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);
    }

    //集合間的操做
    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）、將集合添加到列表中
    
    //將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;
    }

    //將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）、基礎方法

    //獲取列表元素個數
    public int size() {
        return size;
    }

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

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

    //查找元素在列表中第一次出現的位置，循環遍歷
    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後一次出現的位置，倒序遍歷
    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;
    }

    //將列表轉換爲數組
    public Object[] toArray() {
        return Arrays.copyOf(elementData, size);
    }

    //將列表轉換給指定的數組
    @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;
    }

    //縮減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機制，可能會拋出ConcurrentModificationException異常
    //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();
    }

    //迭代器定義
    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;

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

        //獲取下一個元素
        @SuppressWarnings("unchecked")
        public E next() {
            checkForComodification();
            //當前元素下標
            int i = cursor;
            if (i >= size)
                throw new NoSuchElementException();
            Object[] elementData = ArrayList.this.elementData;
            if (i >= elementData.length)
                throw new ConcurrentModificationException();
            //下一個元素的下標
            cursor = i + 1;
            //指定當前最後一個下標
            return (E) elementData[lastRet = i];
        }

        //刪除當前最後一個元素，並指定當前位置的下標
        public void remove() {
            if (lastRet < 0)
                throw new IllegalStateException();
            checkForComodification();

            try {
                //刪除元素
                ArrayList.this.remove(lastRet);
                //指定當前下標
                cursor = lastRet;
                lastRet = -1;
                expectedModCount = modCount;
            } catch (IndexOutOfBoundsException ex) {
                throw new ConcurrentModificationException();
            }
        }

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

 //列表迭代器定義
 private class ListItr extends Itr implements ListIterator<E> {
        ListItr(int index) {
            super();
            cursor = index;
        }
        //是否有前一個
        public boolean hasPrevious() {
            return cursor != 0;
        }

        //獲取下一個索引
        public int nextIndex() {
            return cursor;
        }

        //獲取前一個索引
        public int previousIndex() {
            return cursor - 1;
        }

        //獲取前一個元素
        @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];
        }

        //設置元素
        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，更改子列表時，會影響到父列表，但更改父列表時，子列表將拋出異常ConcurrentModificationException
    //獲取子列表
    public List<E> subList(int fromIndex, int toIndex) {
        subListRangeCheck(fromIndex, toIndex, size);
        return new SubList(this, 0, fromIndex, toIndex);
    }

    //子列表檢測
    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 + ")");
    }

    //如下是子列表對象中的方法

    //子列表構造器
    SubList(AbstractList<E> parent,
            int offset, int fromIndex, int toIndex) {
        this.parent = parent;//父列表對象
        this.parentOffset = fromIndex;
        this.offset = offset + fromIndex;
        this.size = toIndex - fromIndex;//子列表大小
        this.modCount = ArrayList.this.modCount;
        //子列表更改記錄，必須跟父列表保持同步，不然拋出異常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後，須要將更改記錄同步到子列表中
        parent.add(parentOffset + index, e);
        this.modCount = parent.modCount;
        this.size++;
    }

    //刪除指定位置的元素
    public E remove(int index) {
        rangeCheck(index);
        checkForComodification();
        E result = parent.remove(parentOffset + index);
        //往父列表中刪除元素後，須要將更改記錄同步到子列表中
        this.modCount = parent.modCount;
        this.size--;
        return result;
    }

    //檢測子列表與父列表的更改狀態是否一致
       private void checkForComodification() {
        if (ArrayList.this.modCount != this.modCount)
            throw new ConcurrentModificationException();
    }

 

ArrayList的遍歷方式
1）、根據索引值進行遍歷
2）、經過迭代器進行遍歷
3）、經過foreach

ArrayList和LinkedList
1）、ArrayList是基於動態數組實現的數據結構，而LinkedList是基於鏈表實現的數據結構
2）、對於隨機訪問get和set，ArrayList優於LinkedList，這是因爲LinkedList須要移動指針
3）、對於新增和刪除操做add和remove，LinkedList比較佔優點，這是因爲ArrayList須要移動數據

ArrayList和Vector
1）、Vector和ArrayList實現幾乎同樣，惟一不一樣的是Vector是同步類(synchronized)，故開銷比ArrayList大，訪問慢
2）、Vector每次擴容後其大小是原來的2倍，而ArrayList是1.5倍
3）、Vector還有一個子類Stack

 

 

參考資料：

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

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