自己看的源码,整理的.
重点在于分享.
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JDK 1.7
public class ArrayList<E> extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{}
ArrayList继承 AbstractList, 实现 List 接口.
ArrayList实现了RandmoAccess接口，即提供了随机访问功能。RandmoAccess是java中用来被List实现，为List提供快速访问功能的。
我们即可以通过元素的序号快速获取元素对象；
ArrayList 实现了Cloneable接口，即覆盖了函数clone()，能被克隆。
/**
* Default initial capacity.
*/
private static final int DEFAULT_CAPACITY = 10;
默认容量为10.
/**
* 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 == EMPTY_ELEMENTDATA will be expanded to
* DEFAULT_CAPACITY when the first element is added.
*/
private transient Object[] elementData;
存放元素的缓存Object[]
/**
* The size of the ArrayList (the number of elements it contains).
*
* @serial
*/
private int size;
长度.
public ArrayList(int initialCapacity) {
super();
if (initialCapacity < 0)
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
this.elementData = new Object[initialCapacity];
}
可以自定义长度.构建了一个新的Object数组.
/**
* Constructs an empty list with an initial capacity of ten.
*/
public ArrayList() {
super();
this.elementData = EMPTY_ELEMENTDATA;
}
初始容量为10的空集合.
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);
}
/**
* 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 != EMPTY_ELEMENTDATA)
// any size if real element table
? 0
// larger than default for empty table. It's already supposed to be
// at default size.
: DEFAULT_CAPACITY;
if (minCapacity > minExpand) { //判断是否需要扩容
ensureExplicitCapacity(minCapacity);
}
}
ArrayList 扩容方法
private void ensureExplicitCapacity(int minCapacity) {
modCount++;
// overflow-conscious code
if (minCapacity - elementData.length > 0)
grow(minCapacity); //真正的扩容方法
}
/**
* 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;
ArrayList 分配的最大size.
/**
* 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); //扩容1.5倍;
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;
}
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;
}
ArrayList 允许有null值.
public boolean add(E e) {
ensureCapacityInternal(size + 1); // Increments modCount!!
elementData[size++] = e;
return true;
}
添加到末尾.
private class Itr implements Iterator<E>{}
private class ListItr extends Itr implements ListIterator<E> {}
private class SubList extends AbstractList<E> implements RandomAccess {}
由原来的4个内部类,变成了3个内部类.
大家感兴趣可以自己看一下代码.
ArrayList自己实现了序列化和反序列化的方法，
因为它自己实现了 private void writeObject(java.io.ObjectOutputStream s)
和 private void readObject(java.io.ObjectInputStream s) 方法
下面地址是基于 JDK 1.8的
https://blog.csdn.net/fighterandknight/article/details/61240861