存储结构

默认初始容量

private static final int DEFAULT_CAPACITY = 10;

 

private static final Object[] EMPTY_ELEMENTDATA = {};

private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};

采用Object类型的数组存储，所以所有操作都

transient关键字，表明不能序列化Arraylist对象

transient Object[] elementData;  

实际保存的数据量   elementData的容量大小一定要大于size;

private int size;

 

扩容操作

 

/**

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;

/**

* Constructs an empty list with the specified initial capacity.

*

* @param initialCapacity the initial capacity of the list

* @throws IllegalArgumentException if the specified initial capacity

* is negative

*/

public ArrayList(int initialCapacity) {

if (initialCapacity > 0) {

this.elementData = new Object[initialCapacity];

} else if (initialCapacity == 0) {

this.elementData = EMPTY_ELEMENTDATA;

} else {

throw new IllegalArgumentException("Illegal Capacity: "+

initialCapacity);

}

}

/**

* Constructs an empty list with an initial capacity of ten.

*/

public ArrayList() {

this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;

}

/**

* Constructs a list containing the elements of the specified

* collection, in the order they are returned by the collection's

* iterator.

*

* @param c the collection whose elements are to be placed into this list

* @throws NullPointerException if the specified collection is null

*/

public ArrayList(Collection<? extends E> c) {

elementData = c.toArray();

if ((size = elementData.length) != 0) {

// c.toArray might (incorrectly) not return Object[] (see 6260652)

if (elementData.getClass() != Object[].class)

elementData = Arrays.copyOf(elementData, size, Object[].class);

} else {

// replace with empty array.

this.elementData = EMPTY_ELEMENTDATA;

}

}

/**

* Trims the capacity of this <tt>ArrayList</tt> instance to be the

* list's current size. An application can use this operation to minimize

* the storage of an <tt>ArrayList</tt> instance.

*/

public void trimToSize() {

modCount++;

if (size < elementData.length) {

elementData = (size == 0)

? EMPTY_ELEMENTDATA

: Arrays.copyOf(elementData, size);

}

}

/**

* Increases the capacity of this <tt>ArrayList</tt> instance, if

* necessary, to ensure that it can hold at least the number of elements

* specified by the minimum capacity argument.

*

* @param minCapacity the desired minimum capacity

*/

public void ensureCapacity(int minCapacity) {

int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA)

// any size if not default element table

? 0

// larger than default for default empty table. It's already

// supposed to be at default size.

: DEFAULT_CAPACITY;

if (minCapacity > minExpand) {

ensureExplicitCapacity(minCapacity);

}

}

private void ensureCapacityInternal(int minCapacity) {

if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {

minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);

}

ensureExplicitCapacity(minCapacity);

}

private void ensureExplicitCapacity(int minCapacity) {

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;

/**

* Increases the capacity to ensure that it can hold at least the

* number of elements specified by the minimum capacity argument.

*

* @param minCapacity the desired minimum capacity

*/

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);

}

private static int hugeCapacity(int minCapacity) {

if (minCapacity < 0) // overflow

throw new OutOfMemoryError();

return (minCapacity > MAX_ARRAY_SIZE) ?

Integer.MAX_VALUE :

MAX_ARRAY_SIZE;

}