// 將當(dāng)前容量值設(shè)為 =實際元素個數(shù)
    public void trimToSize() {
        modCount++;
        int oldCapacity = elementData.length;
        if (size < oldCapacity) {
            elementData = Arrays.copyOf(elementData, size);
        }
    }

    // 確定ArrarList的容量。
    // 若ArrayList的容量不足以容納當(dāng)前的全部元素，設(shè)置 新的容量=“(原始容量x3)/2 + 1”
    public void ensureCapacity(int minCapacity) {
        // 將“修改統(tǒng)計數(shù)”+1
        modCount++;
        int oldCapacity = elementData.length;
        // 若當(dāng)前容量不足以容納當(dāng)前的元素個數(shù)，設(shè)置 新的容量=“(原始容量x3)/2 + 1”
        if (minCapacity > oldCapacity) {
            Object oldData[] = elementData;
            int newCapacity = (oldCapacity * 3)/2 + 1;
            if (newCapacity < minCapacity)
                newCapacity = minCapacity;
            elementData = Arrays.copyOf(elementData, newCapacity);
        }
    }
    // 添加元素e
    public boolean add(E e) {
        // 確定ArrayList的容量大小
        ensureCapacity(size + 1);  // Increments modCount!!
        // 添加e到ArrayList中
        elementData[size++] = e;
        return true;
    }
    // 返回ArrayList的實際大小
    public int size() {
        return size;
    }
    // 返回ArrayList是否包含Object(o)
    public boolean contains(Object o) {
        return indexOf(o) >= 0;
    }
    // 返回ArrayList是否為空
    public boolean isEmpty() {
        return size == 0;
    }
    // 正向查找，返回元素的索引值
    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;
        }
        // 反向查找，返回元素的索引值
        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;
    }
    // 反向查找(從數(shù)組末尾向開始查找)，返回元素(o)的索引值
    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;
    }

    // 返回ArrayList的Object數(shù)組
    public Object[] toArray() {
        return Arrays.copyOf(elementData, size);
    }
    // 返回ArrayList的模板數(shù)組。所謂模板數(shù)組，即可以將T設(shè)為任意的數(shù)據(jù)類型
    public <T> T[] toArray(T[] a) {
        // 若數(shù)組a的大小 < ArrayList的元素個數(shù)；
        // 則新建一個T[]數(shù)組，數(shù)組大小是“ArrayList的元素個數(shù)”，并將“ArrayList”全部拷貝到新數(shù)組中
        if (a.length < size)
            return (T[]) Arrays.copyOf(elementData, size, a.getClass());
        // 若數(shù)組a的大小 >= ArrayList的元素個數(shù)；
        // 則將ArrayList的全部元素都拷貝到數(shù)組a中。
        System.arraycopy(elementData, 0, a, 0, size);
        if (a.length > size)
            a[size] = null;
        return a;
    }
    // 獲取index位置的元素值
    public E get(int index) {
        RangeCheck(index);
        return (E) elementData[index];
    }
    // 設(shè)置index位置的值為element
    public E set(int index, E element) {
        RangeCheck(index);
        E oldValue = (E) elementData[index];
        elementData[index] = element;
        return oldValue;
    }
    // 將e添加到ArrayList中
    public boolean add(E e) {
        ensureCapacity(size + 1);  // Increments modCount!!
        elementData[size++] = e;
        return true;
    }
    // 將e添加到ArrayList的指定位置
    public void add(int index, E element) {
        if (index > size || index < 0)
            throw new IndexOutOfBoundsException(
            "Index: "+index+", Size: "+size);
        ensureCapacity(size+1);  // Increments modCount!!
        System.arraycopy(elementData, index, elementData, index + 1,
             size - index);
        elementData[index] = element;
        size++;
    }
    // 刪除ArrayList指定位置的元素
    public E remove(int index) {
        RangeCheck(index);
        modCount++;
        E oldValue = (E) 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ArrayList的指定元素
    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;
    }

    // 快速刪除第index個元素
    private void fastRemove(int index) {
        modCount++;
        int numMoved = size - index - 1;
        // 從"index+1"開始，用后面的元素替換前面的元素。
        if (numMoved > 0)
            System.arraycopy(elementData, index+1, elementData, index,
                             numMoved);
        // 將最后一個元素設(shè)為null
        elementData[--size] = null; // Let gc do its work
    }
    // 刪除元素
    public boolean remove(Object o) {
        if (o == null) {
            for (int index = 0; index < size; index++)
            if (elementData[index] == null) {
                fastRemove(index);
            return true;
            }
        } else {
            // 便利ArrayList，找到“元素o”，則刪除，并返回true。
            for (int index = 0; index < size; index++)
            if (o.equals(elementData[index])) {
                fastRemove(index);
            return true;
            }
        }
        return false;
    }
    // 清空ArrayList，將全部的元素設(shè)為null
    public void clear() {
        modCount++;
        for (int i = 0; i < size; i++)
            elementData[i] = null;
        size = 0;
    }
    // 將集合c追加到ArrayList中
    public boolean addAll(Collection<? extends E> c) {
        Object[] a = c.toArray();
        int numNew = a.length;
        ensureCapacity(size + numNew);  // Increments modCount
        System.arraycopy(a, 0, elementData, size, numNew);
        size += numNew;
        return numNew != 0;
    }
    // 從index位置開始，將集合c添加到ArrayList
    public boolean addAll(int index, Collection<? extends E> c) {
        if (index > size || index < 0)
            throw new IndexOutOfBoundsException(
            "Index: " + index + ", Size: " + size);
        Object[] a = c.toArray();
        int numNew = a.length;
        ensureCapacity(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;
    }
    // 刪除fromIndex到toIndex之間的全部元素。
    protected void removeRange(int fromIndex, int toIndex) {
    modCount++;
    int numMoved = size - toIndex;
        System.arraycopy(elementData, toIndex, elementData, fromIndex,
                         numMoved);
    // Let gc do its work
    int newSize = size - (toIndex-fromIndex);
    while (size != newSize)
        elementData[--size] = null;
    }
    private void RangeCheck(int index) {
    if (index >= size)
        throw new IndexOutOfBoundsException(
        "Index: "+index+", Size: "+size);
    }

    // 克隆函數(shù)
    public Object clone() {
        try {
            ArrayList<E> v = (ArrayList<E>) super.clone();
            // 將當(dāng)前ArrayList的全部元素拷貝到v中
            v.elementData = Arrays.copyOf(elementData, size);
            v.modCount = 0;
            return v;
        } catch (CloneNotSupportedException e) {
            // this shouldn't happen, since we are Cloneable
            throw new InternalError();
        }
    }

    // java.io.Serializable的寫入函數(shù)
    // 將ArrayList的“容量，所有的元素值”都寫入到輸出流中
    private void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException{
    // Write out element count, and any hidden stuff
    int expectedModCount = modCount;
    s.defaultWriteObject();
        // 寫入“數(shù)組的容量”
        s.writeInt(elementData.length);
    // 寫入“數(shù)組的每一個元素”
    for (int i=0; i<size; i++)
            s.writeObject(elementData[i]);
    if (modCount != expectedModCount) {
            throw new ConcurrentModificationException();
        }
    }

    // java.io.Serializable的讀取函數(shù)：根據(jù)寫入方式讀出
    // 先將ArrayList的“容量”讀出，然后將“所有的元素值”讀出
    private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        // Read in size, and any hidden stuff
        s.defaultReadObject();
        // 從輸入流中讀取ArrayList的“容量”
        int arrayLength = s.readInt();
        Object[] a = elementData = new Object[arrayLength];
        // 從輸入流中將“所有的元素值”讀出
        for (int i=0; i<size; i++)
            a[i] = s.readObject();
    }
}

    public static void iteratorThroughFor2(List list) {
        long startTime;
        long endTime;
        startTime = System.currentTimeMillis();
        for(Object obj:list)

        endTime = System.currentTimeMillis();
        long interval = endTime - startTime;
        System.out.println("iteratorThroughFor2：" + interval+" ms");
    }
}