java.lang.Object

    java.util.AbstractCollection<E>

        java.util.AbstractList<E>

            java.util.ArrayList<E>

所有已实现的接口：

, , <E>, <E>, <E>,

直接已知子类：

, ,

1.Iterator方法

ArrayList l = new ArrayList();

Iterator iterator = l.iterator();

调用父类AbstractList的iterator()方法，得到Itr实例（AbstractList的内部类，实现了Iterator接口），利用cursor游标实现hashNext()，及next()方法

public abstract class AbstractList
     
       extends AbstractCollection
      
        implements List
       
         {      protected AbstractList() {     }  public Iterator
        
          iterator() {     return new Itr();     }  private class Itr implements Iterator
         
           {     /**      * Index of element to be returned by subsequent call to next.      */     int cursor = 0;      /**      * Index of element returned by most recent call to next or      * previous.  Reset to -1 if this element is deleted by a call      * to remove.      */     int lastRet = -1;      /**      * The modCount value that the iterator believes that the backing      * List should have.  If this expectation is violated, the iterator      * has detected concurrent modification.      */     int expectedModCount = modCount;      public boolean hasNext() {             return cursor != size();     }      public E next() {             checkForComodification();         try {         E next = get(cursor);         lastRet = cursor++;         return next;         } catch (IndexOutOfBoundsException e) {         checkForComodification();         throw new NoSuchElementException();         }     }      public void remove() {         if (lastRet == -1)         throw new IllegalStateException();             checkForComodification();          try {         AbstractList.this.remove(lastRet);         if (lastRet < cursor)             cursor--;         lastRet = -1;         expectedModCount = modCount;         } catch (IndexOutOfBoundsException e) {         throw new ConcurrentModificationException();         }     }      final void checkForComodification() {         if (modCount != expectedModCount)         throw new ConcurrentModificationException();     }     } }
         
        
       
      
     

2.Add方法

//添加元素 public boolean add(E e) {    ensureCapacity(size + 1);  // Increments modCount!!    elementData[size++] = e; //elementData为缓存数组，若不设置list的初始大小，此数组默认大小为10    return true;    }   //当添加的元素数量超出数组初始值时，进行扩容操作    public void ensureCapacity(int minCapacity) {    modCount++;    int oldCapacity = elementData.length;    if (minCapacity > oldCapacity) {        Object oldData[] = elementData;        int newCapacity = (oldCapacity * 3)/2 + 1;            if (newCapacity < minCapacity)        newCapacity = minCapacity;            // minCapacity is usually close to size, so this is a win:            elementData = Arrays.copyOf(elementData, newCapacity);    }    }

 3.addAll方法

public boolean addAll(Collection
      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;    }

4.clear方法

public void clear() {        //操作次数加一    modCount++;    // Let gc do its work    for (int i = 0; i < size; i++)        elementData[i] = null;    size = 0;    }

5.clone方法

public Object clone() {    try {        ArrayList
     
       v = (ArrayList
      
       ) super.clone();        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();    }    }    public static 
       
         T[] copyOf(T[] original, int newLength) {        return (T[]) copyOf(original, newLength, original.getClass());    }    public static 
        
          T[] copyOf(U[] original, int newLength, Class
          newType) {        T[] copy = ((Object)newType == (Object)Object[].class)            ? (T[]) new Object[newLength]            : (T[]) Array.newInstance(newType.getComponentType(), newLength);        System.arraycopy(original, 0, copy, 0,                         Math.min(original.length, newLength));        return copy;    }
        
       
      
     

6.get方法

public E get(int index) {    RangeCheck(index);    return (E) elementData[index];    }    //检测数组越界    private void RangeCheck(int index) {    if (index >= size)        throw new IndexOutOfBoundsException(        "Index: "+index+", Size: "+size);    }

7.indexOf方法

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;    }

8.remove方法

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;    }

 9.removeAll方法

public boolean removeAll(Collection
      c) {    boolean modified = false;    Iterator
      e = iterator();    while (e.hasNext()) {        if (c.contains(e.next())) {        e.remove();        modified = true;        }    }    return modified;    }    //contains方法调用了indexOf方法    public boolean contains(Object o) {    return indexOf(o) >= 0;    }