ArrayList

public class ArrayList<E> extends AbstractList<E>
        implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
    private static final long serialVersionUID = 8683452581122892189L;
/**
 * Default initial capacity.
 */
private static final int DEFAULT_CAPACITY = 10;

/**
 * Shared empty array instance used for empty instances.
 */
private static final Object[] EMPTY_ELEMENTDATA = {};

/**
 * Shared empty array instance used for default sized empty instances. We
 * distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when
 * first element is added.
 */
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};

/**
 * The array buffer into which the elements of the ArrayList are stored.
 * The capacity of the ArrayList is the length of this array buffer. Any
 * empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
 * will be expanded to DEFAULT_CAPACITY when the first element is added.
 */
transient Object[] elementData; // non-private to simplify nested class access

/**
 * The size of the ArrayList (the number of elements it contains).
 *
 * @serial
 */
private int size;

}
public E remove(int index) {

rangeCheck(index);

//记录结构修改次数,遍历器里检测到修改报异常

modCount++;

E oldValue = elementData(index);
int numMoved = size - index - 1;
if (numMoved &gt; 0)
    System.arraycopy(elementData, index+1, elementData, index, numMoved);
elementData[--size] = null; // clear to let GC do its work

return oldValue;

}
private void fastRemove(int index) {

modCount++;

int numMoved = size - index - 1;

if (numMoved > 0)

System.arraycopy(elementData, index+1, elementData, index,numMoved);

elementData[--size] = null; // clear to let GC do its work

}
public static void arraycopy(@NotNull Object src,

int srcPos,

@NotNull Object dest,

int destPos,

int length)
public void trimToSize() {

modCount++;

if (size < elementData.length) {

elementData = (size == 0)

? EMPTY_ELEMENTDATA

: Arrays.copyOf(elementData, size);

}

}
private void grow(int minCapacity) {

// overflow-conscious code

int oldCapacity = elementData.length;

int newCapacity = oldCapacity + (oldCapacity >> 1);

if (newCapacity - minCapacity < 0)

newCapacity = minCapacity;

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);

}

int oldCapacity = elementData.length;
int newCapacity = oldCapacity + (oldCapacity >> 1);