// 默認(rèn)構(gòu)造函數(shù)
ArrayList()
// capacity是ArrayList的默認(rèn)容量大小。當(dāng)由于增加數(shù)據(jù)導(dǎo)致容量不足時(shí)，容量會(huì)添加上一次容量大小的一半。
ArrayList(int capacity)
// 創(chuàng)建一個(gè)包含collection的ArrayList
ArrayList(Collection<? extends E> collection)

// Collection中定義的API
boolean             add(E object)
boolean             addAll(Collection<? extends E> collection)
void                clear()
boolean             contains(Object object)
boolean             containsAll(Collection<?> collection)
boolean             equals(Object object)
int                 hashCode()
boolean             isEmpty()
Iterator<E>         iterator()
boolean             remove(Object object)
boolean             removeAll(Collection<?> collection)
boolean             retainAll(Collection<?> collection)
int                 size()
<T> T[]             toArray(T[] array)
Object[]            toArray()
// AbstractCollection中定義的API
void                add(int location, E object)
boolean             addAll(int location, Collection<? extends E> collection)
E                   get(int location)
int                 indexOf(Object object)
int                 lastIndexOf(Object object)
ListIterator<E>     listIterator(int location)
ListIterator<E>     listIterator()
E                   remove(int location)
E                   set(int location, E object)
List<E>             subList(int start, int end)
// ArrayList新增的API
Object               clone()
void                 ensureCapacity(int minimumCapacity)
void                 trimToSize()
void                 removeRange(int fromIndex, int toIndex)

package java.util;
public class ArrayList<E> extends AbstractList<E>
        implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
    // 序列版本號(hào)
    private static final long serialVersionUID = 8683452581122892189L;
    // 保存ArrayList中數(shù)據(jù)的數(shù)組
    private transient Object[] elementData;
    // ArrayList中實(shí)際數(shù)據(jù)的數(shù)量
    private int size;
    // ArrayList帶容量大小的構(gòu)造函數(shù)。
    public ArrayList(int initialCapacity) {
        super();
        if (initialCapacity < 0)
            throw new IllegalArgumentException("Illegal Capacity: "+
                                               initialCapacity);
        // 新建一個(gè)數(shù)組
        this.elementData = new Object[initialCapacity];
    }
    // ArrayList構(gòu)造函數(shù)。默認(rèn)容量是10。
    public ArrayList() {
        this(10);
    }
    // 創(chuàng)建一個(gè)包含collection的ArrayList
    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);
    }

    // 將當(dāng)前容量值設(shè)為 =實(shí)際元素個(gè)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(jì)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(gè)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(shí)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(kāi)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(lèi)型
    public <T> T[] toArray(T[] a) {
        // 若數(shù)組a的大小 < ArrayList的元素個(gè)數(shù)；
        // 則新建一個(gè)T[]數(shù)組，數(shù)組大小是“ArrayList的元素個(gè)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(gè)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(gè)元素
    private void fastRemove(int index) {
        modCount++;
        int numMoved = size - index - 1;
        // 從"index+1"開(kāi)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(gè)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(kāi)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(xiě)入函數(shù)
    // 將ArrayList的“容量，所有的元素值”都寫(xiě)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(xiě)入“數(shù)組的容量”
        s.writeInt(elementData.length);
    // 寫(xiě)入“數(shù)組的每一個(gè)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(xiě)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();
    }
}

Integer value = null;
Iterator iter = list.iterator();
while (iter.hasNext()) {
    value = (Integer)iter.next();
}

Integer value = null;
int size = list.size();
for (int i=0; i<size; i++) {
    value = (Integer)list.get(i);       
}

Integer value = null;
for (Integer integ:list) {
    value = integ;
}
 

import java.util.*;
import java.util.concurrent.*;
/*
 * @desc ArrayList遍歷方式和效率的測(cè)試程序。
 *
 * @author skywang
 */
public class ArrayListRandomAccessTest {
    public static void main(String[] args) {
        List list = new ArrayList();
        for (int i=0; i<100000; i++)
            list.add(i);
        //isRandomAccessSupported(list);
        iteratorThroughRandomAccess(list) ;
        iteratorThroughIterator(list) ;
        iteratorThroughFor2(list) ;

    }
    private static void isRandomAccessSupported(List list) {
        if (list instanceof RandomAccess) {
            System.out.println("RandomAccess implemented!");
        } else {
            System.out.println("RandomAccess not implemented!");
        }
    }
    public static void iteratorThroughRandomAccess(List list) {
        long startTime;
        long endTime;
        startTime = System.currentTimeMillis();
        for (int i=0; i<list.size(); i++) {
            list.get(i);
        }
        endTime = System.currentTimeMillis();
        long interval = endTime - startTime;
        System.out.println("iteratorThroughRandomAccess：" + interval+" ms");
    }
    public static void iteratorThroughIterator(List list) {
        long startTime;
        long endTime;
        startTime = System.currentTimeMillis();
        for(Iterator iter = list.iterator(); iter.hasNext(); ) {
            iter.next();
        }
        endTime = System.currentTimeMillis();
        long interval = endTime - startTime;
        System.out.println("iteratorThroughIterator：" + interval+" ms");
    }

    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");
    }
}

// toArray(T[] contents)調(diào)用方式一
public static Integer[] vectorToArray1(ArrayList<Integer> v) {
    Integer[] newText = new Integer[v.size()];
    v.toArray(newText);
    return newText;
}
// toArray(T[] contents)調(diào)用方式二。最常用！
public static Integer[] vectorToArray2(ArrayList<Integer> v) {
    Integer[] newText = (Integer[])v.toArray(new Integer[0]);
    return newText;
}
// toArray(T[] contents)調(diào)用方式三
public static Integer[] vectorToArray3(ArrayList<Integer> v) {
    Integer[] newText = new Integer[v.size()];
    Integer[] newStrings = (Integer[])v.toArray(newText);
    return newStrings;
}

import java.util.*;
/*
 * @desc ArrayList常用API的測(cè)試程序
 * @author skywang
 * @email [email protected]
 */
public class ArrayListTest {
    public static void main(String[] args) {

        // 創(chuàng)建ArrayList
        ArrayList list = new ArrayList();
        // 將“”
        list.add("1");
        list.add("2");
        list.add("3");
        list.add("4");
        // 將下面的元素添加到第1個(gè)位置
        list.add(0, "5");
        // 獲取第1個(gè)元素
        System.out.println("the first element is: "+ list.get(0));
        // 刪除“3”
        list.remove("3");
        // 獲取ArrayList的大小
        System.out.println("Arraylist size=: "+ list.size());
        // 判斷l(xiāng)ist中是否包含"3"
        System.out.println("ArrayList contains 3 is: "+ list.contains(3));
        // 設(shè)置第2個(gè)元素為10
        list.set(1, "10");
        // 通過(guò)Iterator遍歷ArrayList
        for(Iterator iter = list.iterator(); iter.hasNext(); ) {
            System.out.println("next is: "+ iter.next());
        }
        // 將ArrayList轉(zhuǎn)換為數(shù)組
        String[] arr = (String[])list.toArray(new String[0]);
        for (String str:arr)
            System.out.println("str: "+ str);
        // 清空ArrayList
        list.clear();
        // 判斷ArrayList是否為空
        System.out.println("ArrayList is empty: "+ list.isEmpty());
    }
}