ArrayList源码研读
文章目录
属性
public class ArrayList<E> extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
/*
* （序列化(Serializable接口)
*
* 含义：将一个对象的状态(各个属性值)保存起来，然后在适当的时候再获得
*
* 用途：序列化的过程就是对象写入字节流(序列化)和从字节流中读取对象(反序列化),
* 允许一个对象在虚拟机之间传送(或者经过一段空间，如在RMI中;或者经过一段时间，比如数据流被保存到一个文件中)。
* 对象序列化可以对对象进行深层复制。
*
* Java对象序列化将那些实现了Serializable接口的对象转换成一个字节序列，
* 并能够以后将这个字节序列完全恢复为原来的对象。利用对象的序列化，可以实现轻量级持久性，
* 这意味着一个对象的生存周期并不取决于程序是否正在执行，它可以生存于程序的调用之间。
* 通过将一个序列化对象写入磁盘，然后在重新调用程序时恢复该对象，就能够实现持久性的效果。
*
*/ {
private static final long serialVersionUID = 8683452581122892189L;
/**
* Default initial capacity.
* 默认容量10
*/
private static final int DEFAULT_CAPACITY = 10;
/**
* Shared empty array instance used for empty instances.
* 空数组实例
*/
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.
* 默认容量实例
*/
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
/**
* The array buffer into which the elements of the ArrayList are stored.
* 存储ArrayList的元素的数组缓冲区
* 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.
* ArrayList的容量是该数组缓冲区的长度。
* 添加第一个元素时，任何具有elementData==DEFAULTCAPACITY_EMPTY_ELEMENTDATA的空ArrayList都将扩展为默认容量。
* elementData属性采用了transient来修饰，表明其不使用Java默认的序列化机制来实例化
* elementData里面有一些元素是空的，这种是没有必要序列化的。
* ArrayList的序列化和反序列化依赖writeObject和readObject方法来实现。可以避免序列化空的元素。
*/
transient Object[] elementData; // non-private to simplify nested class access
/**
* The size of the ArrayList (the number of elements it contains).
*/
private int size;
构造器
public ArrayList (int initialCapacity)
public ArrayList ()
public ArrayList (Collection<? extends E> c)
/**
* Constructs an empty list with the specified initial capacity.
* 以指定初始容量构造一个空的集合
* @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.
* （不指定初始容量时）以默认初始容量10构造一个空的集合
*/
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.
* 构造一个包含指定集合的元素的列表，该列表按集合的迭代顺序排列。
* @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;
}
}
容量削减
public void trimToSize ()
/**
* 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.
* 将此ArrayList实例的容量削减为
* list的当前大小。
* 程序可以使用此操作最小化ArrayList实例的存储。
*/
public void trimToSize () {
modCount++;
if (size < elementData.length) {
elementData = (size == 0)
? EMPTY_ELEMENTDATA
: Arrays.copyOf (elementData, size);
}
}
扩容
ensureCapacity (int minCapacity)
calculateCapacity (Object[] elementData, int minCapacity)
ensureCapacityInternal (int minCapacity)
ensureExplicitCapacity (int minCapacity)
grow (int minCapacity)
/**
* 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.
* 扩容
*
* @param minCapacity
* the desired minimum capacity
*/
public void ensureCapacity (int minCapacity) {
//判断需要扩容的数组是否为空实例（空数组）如果为不为空，则变量等于0.为空则变量等于数组默认容量 10
int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA) ? 0 : DEFAULT_CAPACITY;
// any size if not default element table
// larger than default for default empty table. It's already
// supposed to be at default size.
//如果需要扩容的量大于定义的变量。则进一步调用以下方法。
if (minCapacity > minExpand) {
ensureExplicitCapacity (minCapacity);
}
}
/**
* 计算需要的容量
*/
private static int calculateCapacity (Object[] elementData, int minCapacity) {
//如果传进来的elementData是DEFAULTCAPACITY_EMPTY_ELEMENTDATA
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
// 获取默认的容量和传入参数的较大值
return Math.max (DEFAULT_CAPACITY, minCapacity);
}
//直接返回需要的最小容量
return minCapacity;
}
/**
* 确认需要扩容的容量并进行扩容
* @param minCapacity
*/
private void ensureCapacityInternal (int minCapacity) {
ensureExplicitCapacity (calculateCapacity (elementData, minCapacity));
}
/**
* 进行扩容
* @param minCapacity
*/
private void ensureExplicitCapacity (int minCapacity) {
//改变了list的大小
modCount++;
// overflow-conscious code
if (minCapacity - elementData.length > 0)
//扩容
grow (minCapacity);
}
/**
* The maximum size of array to allocate.
* Some VMs reserve some header words in an array.
* 某些虚拟机需要8字节存储头信息
* Attempts to allocate larger arrays may result in
* OutOfMemoryError: Requested array size exceeds VM limit
* 最大size
*/
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（需要扩容到的最小容量）
*/
private void grow (int minCapacity) {
// overflow-conscious code
//旧容量
int oldCapacity = elementData.length;
//新容量 = o+o/2 就是1.5倍的old
int newCapacity = oldCapacity + (oldCapacity >> 1);
//扩容后没达到需要扩容到的最小容量，扩容到minCapacity
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
//新容量大于MAX_ARRAY_SIZE（Integer.MAX_VALUE - 8）
if (newCapacity - MAX_ARRAY_SIZE > 0)
//扩容到Integer.MAX_VALUE
newCapacity = hugeCapacity (minCapacity);
// minCapacity is usually close to size, so this is a win:
//复制元素到新数组
elementData = Arrays.copyOf (elementData, newCapacity);
}
//扩展到最大（某些虚拟机不需要存储头信息就可以扩容到 Integer.MAX_VALUE）
private static int hugeCapacity (int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError ();
return (minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}
获得size
size ()
/**
* Returns the number of elements in this list.
* 返回集合中的元素个数
* @return the number of elements in this list
* 获得size
*/
public int size () {
return size;
}
判断集合是否为空
isEmpty ()
/**
* Returns <tt>true</tt> if this list contains no elements.
*
* @return <tt>true</tt> if this list contains no elements
* 是否为空
*/
public boolean isEmpty () {
return size == 0;
}
判断集合中是否包含某个元素
contains (Object o)
/**
* Returns <tt>true</tt> if this list contains the specified element.
* More formally, returns <tt>true</tt> if and only if this list contains
* at least one element <tt>e</tt> such that
* <tt>(o==null ? e==null : o.equals(e))</tt>.
*
* @param o
* element whose presence in this list is to be tested
*
* @return <tt>true</tt> if this list contains the specified element
* 是否含有o
*/
public boolean contains (Object o) {
return indexOf (o) >= 0;
}
获得元素在集合中的索引
indexOf (Object o)
lastIndexOf (Object o)
/**
* Returns the index of the first occurrence of the specified element
* in this list,
* 返回指定元素在list中的第一个匹配项的索引
* or -1 if this list does not contain the element.
* 如果list中没有该元素则返回-1
* More formally, returns the lowest index <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
*/
public int indexOf (Object o) {
//如果o是空
if (o == null) {
for (int i = 0; i < size; i++)
//返回第一个为空的位置
if (elementData[i] == null)
return i;
} else {
for (int i = 0; i < size; i++)
//返回元素所在位置
if (o.equals (elementData[i]))
return i;
}
//找不到该元素
return - 1;
}
/**
* Returns the index of the last occurrence of the specified element
* 返回指定元素在list中的最后一个匹配项的索引
* in this list, or -1 if this list does not contain the element.
* 如果list中没有该元素则返回-1
* More formally, returns the highest index <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
*/
public int lastIndexOf (Object o) {
if (o == null) {
for (int i = size - 1; i >= 0; i--)
if (elementData[i] == null)
return i;
} else {
//从后往前遍历
for (int i = size - 1; i >= 0; i--)
if (o.equals (elementData[i]))
return i;
}
return - 1;
}
浅拷贝
clone ()
/**
* Returns a shallow copy of this <tt>ArrayList</tt> instance.
* 返回该实例的浅拷贝
* (The elements themselves are not copied.)
* 浅拷贝只复制指向某个对象的指针，而不复制对象本身，新旧对象还是共享同一块内存。
*
* @return a clone of this <tt>ArrayList</tt> instance
*/
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 (e);
}
}
返回包含所有元素de数组
Object[] toArray ()
< T > T[] toArray (T[] a)
/**
* Returns an array containing all of the elements in this list
* 按顺序返回一个包含所有元素的数组
* in proper sequence (from first to last element).
* <p>The returned array will be "safe" in that no references to it are
* maintained by this list.
* 返回的数组将是“安全的”，因为此列表不维护对它的引用。
* (In other words, this method must allocate
* a new array).
* The caller is thus free to modify the returned array.
* 因此，方法调用者可以自由修改返回的数组。
* <p>This method acts as bridge between array-based and collection-based
* APIs.
*
* @return an array containing all of the elements in this list in
* proper sequence
*/
public Object[] toArray () {
return Arrays.copyOf (elementData, size);
}
/**
* Returns an array containing all of the elements in this list in proper
* sequence (from first to last element); the runtime type of the returned
* array is that of the specified array.
* 返回的数组的运行时类型是指定数组的运行时类型
* If the list fits in the
* specified array, it is returned therein. Otherwise, a new array is
* allocated with the runtime type of the specified array and the size of
* this list.
* 如果列表和指定的数组大小一致，并且有剩余空间
* <p>If the list fits in the specified array with room to spare
* (i.e., the array has more elements than the list), the element in
* the array immediately following the end of the collection is set to
* <tt>null</tt>.
* 紧跟在集合末尾的数组中的元素设置为null
* (This is useful in determining the length of the
* list <i>only</i> if the caller knows that the list does not contain
* any null elements.)
* 如果调用者知道该list里面没有包含有null，可以用这个来计算list的长度
*
* @param a
* the array into which the elements of the list are to
* be stored, if it is big enough; otherwise, a new array of the
* same runtime type is allocated for this purpose.
*
* @return an array containing the elements of the list
*
* @throws ArrayStoreException
* if the runtime type of the specified array
* is not a supertype of the runtime type of every element in
* this list
* @throws NullPointerException
* if the specified array is null
*/
@SuppressWarnings ("unchecked")
public <T> T[] toArray (T[] a) {
if (a.length < size)
// Make a new array of a's runtime type, but my contents:
//创建一个新数组存放
return (T[]) Arrays.copyOf (elementData, size, a.getClass ());
//不会产生新的数组对象
System.arraycopy (elementData, 0, a, 0, size);
//List的size的位置，把其设为null
if (a.length > size)
a[size] = null;
return a;
}
获得元素
get (int index)
/**
* Returns the element at the specified position in this list.
* 获得对应位置的元素
*
* @param index
* index of the element to return
*
* @return the element at the specified position in this list
*
* @throws IndexOutOfBoundsException
* {@inheritDoc}
*/
public E get (int index) {
rangeCheck (index);
return elementData (index);
}
替换元素
set (int index, E element)
/**
* Replaces the element at the specified position in this list with
* the specified element.
* 替换对应位置的元素，并返回旧的元素
* @param index
* index of the element to replace
* @param element
* element to be stored at the specified position
*
* @return the element previously at the specified position
*
* @throws IndexOutOfBoundsException
* {@inheritDoc}
*/
public E set (int index, E element) {
rangeCheck (index);
E oldValue = elementData (index);
elementData[index] = element;
return oldValue;
}
增加元素
add (E e)
add (int index, E element)
/**
* Appends the specified element to the end of this list.
*追加新元素在list的末尾
* @param e
* element to be appended to this list
*
* @return <tt>true</tt> (as specified by {@link Collection#add})
*/
public boolean add (E e) {
ensureCapacityInternal (size + 1); // Increments modCount!!
//先执行size++在赋值元素
// 会有线程安全问题，当多个线程同时进入该方法
elementData[size++] = e;
return true;
}
/**
* Inserts the specified element at the specified position in this
* list.
* 在指定位置添加元素
* Shifts the element currently at that position (if any) and
* any subsequent elements to the right (adds one to their indices).
* 将当前位于该位置的元素(如果有)和所有后续元素向右移动(将其索引加1)
* @param index
* index at which the specified element is to be inserted
* @param element
* element to be inserted
*
* @throws IndexOutOfBoundsException
* {@inheritDoc}
*/
public void add (int index, E element) {
//检查index的范围
rangeCheckForAdd (index);
//确认是否需要扩容并进行扩容
ensureCapacityInternal (size + 1); // Increments modCount!!
//把index之后的元素都后移一位
System.arraycopy (elementData, index, elementData, index + 1,
size - index);
//在index位置加入新元素
elementData[index] = element;
size++;
}
/**
* Appends all of the elements in the specified collection to the end of
* this list, in the order that they are returned by the
* specified collection's Iterator.
* 在列表尾部顺序追加所有元素
* The behavior of this operation is
* undefined if the specified collection is modified while the operation
* is in progress.
* 如果在该操作进行时collection被修改了，会使得该行为具有不确定性
* (This implies that the behavior of this call is
* undefined if the specified collection is this list, and this
* list is nonempty.)
*
* @param c
* collection containing elements to be added to this list
*
* @return <tt>true</tt> if this list changed as a result of the call
*
* @throws NullPointerException
* if the specified collection is null
*/
public boolean addAll (Collection<? extends E> c) {
Object[] a = c.toArray ();
int numNew = a.length;
ensureCapacityInternal (size + numNew); // Increments modCount
System.arraycopy (a, 0, elementData, size, numNew);
size += numNew;
//c有元素则true没有false
return numNew != 0;
}
/**
* Inserts all of the elements in the specified collection into this
* list, starting at the specified position.
* 从指定位置开始顺序追加元素
* Shifts the element
* currently at that position (if any) and any subsequent elements to
* the right (increases their indices).
* 将当前位于该位置的元素(如果有)和所有后续元素向右移动(将其索引加1)
* The new elements will appear
* in the list in the order that they are returned by the
* specified collection's iterator.
*
* @param index
* index at which to insert the first element from the
* specified collection
* @param c
* collection containing elements to be added to this list
*
* @return <tt>true</tt> if this list changed as a result of the call
*
* @throws IndexOutOfBoundsException
* {@inheritDoc}
* @throws NullPointerException
* if the specified collection is null
*/
public boolean addAll (int index, Collection<? extends E> c) {
rangeCheckForAdd (index);
Object[] a = c.toArray ();
int numNew = a.length;
ensureCapacityInternal (size + numNew); // Increments modCount
int numMoved = size - index;
if (numMoved > 0)
//原来元素后移numMoved位
System.arraycopy (elementData, index, elementData, index + numNew,
numMoved);
//新元素放置
System.arraycopy (a, 0, elementData, index, numNew);
size += numNew;
return numNew != 0;
}
移除元素
remove (int index)
remove (Object o)
fastRemove (int index)
clear ()
removeAll (Collection<?> c)
removeRange (int fromIndex, int toIndex)
retainAll (Collection<?> c)
batchRemove (Collection<?> c, boolean complement)
/**
* Removes the element at the specified position in this list.
* 移除指定位置的元素,并返回该元素
* Shifts any subsequent elements to the left (subtracts one from their
* indices).
* 将当前位于该位置所有后续元素向左移动（索引减1）
* @param index
* the index of the element to be removed
*
* @return the element that was removed from the list
*
* @throws IndexOutOfBoundsException
* {@inheritDoc}
*/
public E remove (int index) {
//检查索引是否在范围内
rangeCheck (index);
//结构上的改变
modCount++;
E oldValue = elementData (index);
//numMoved用来判断是否需要移动元素
int numMoved = size - index - 1;
//需要移动
if (numMoved > 0)
//index之后的元素都前移一位
System.arraycopy (elementData, index + 1, elementData, index,
numMoved);
//不需要移动（index的元素是最后一位）
//把最后一位的元素设为null（让GC回收）然后size减一
elementData[-- size] = null; // clear to let GC do its work
return oldValue;
}
/**
* Removes the first occurrence of the specified element from this list,
* if it is present.
* 如果存在o元素，移除list中第一次遇到的那个元素，就是靠前的那个
* If the list does not contain the element, it is
* unchanged.
* 如果不存在o元素，则列表不变
* More formally, removes the element with the lowest index
* 更正式地说，移除index最小的那个元素
* <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
* (if such an element exists). Returns <tt>true</tt> if this list
* contained the specified element (or equivalently, if this list
* changed as a result of the call).
* 如果list中有该元素，则返回true
* @param o
* element to be removed from this list, if present
*
* @return <tt>true</tt> if this list contained the specified element
*/
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;
}
/*
* Private remove method that skips bounds checking and does not
* return the value removed.
* 不进行检查且不返回元素的remove
*/
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
}
/**
* Removes all of the elements from this list.
* The list will
* be empty after this call returns.
* 移除列表中的所有元素
*/
public void clear () {
modCount++;
// clear to let GC do its work
for (int i = 0; i < size; i++)
elementData[i] = null;
size = 0;
}
/**
* Removes from this list all of its elements that are contained in the
* specified collection.
* 移除列表中包含的collection中指定的所有元素
*
* @param c
* collection containing elements to be removed from this list
*
* @return {@code true} if this list changed as a result of the call
*
* @throws ClassCastException
* if the class of an element of this list
* is incompatible with the specified collection
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException
* if this list contains a null element and the
* specified collection does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>),
* or if the specified collection is null
* @see Collection#contains(Object)
*/
public boolean removeAll (Collection<?> c) {
//NullPointerException
Objects.requireNonNull (c);
return batchRemove (c, false);
}
/**
* Removes from this list all of the elements whose index is between
* {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
* 移除fromIndex到toIndex之间的元素
* Shifts any succeeding elements to the left (reduces their index).
* 移动后续元素到左边，减少索引值
* This call shortens the list by {@code (toIndex - fromIndex)} elements.
* (If {@code toIndex==fromIndex}, this operation has no effect.)
*
* @throws IndexOutOfBoundsException
* if {@code fromIndex} or
* {@code toIndex} is out of range
* ({@code fromIndex < 0 ||
* fromIndex >= size() ||
* toIndex > size() ||
* toIndex < fromIndex})
*/
protected void removeRange (int fromIndex, int toIndex) {
modCount++;
int numMoved = size - toIndex;
//移动后续元素到左边
System.arraycopy (elementData, toIndex, elementData, fromIndex,
numMoved);
// clear to let GC do its work
// 成功删除了toIndex - fromIndex元素，将后面空间置空
int newSize = size - (toIndex - fromIndex);
for (int i = newSize; i < size; i++) {
elementData[i] = null;
}
size = newSize;
}
/**
* Retains only the elements in this list that are contained in the
* specified collection. In other words, removes from this list all
* of its elements that are not contained in the specified collection.
* 仅保留集合中collection包含的元素，也即是说，移除collection中不包含的元素
* @param c
* collection containing elements to be retained in this list
*
* @return {@code true} if this list changed as a result of the call
*
* @throws ClassCastException
* if the class of an element of this list
* is incompatible with the specified collection
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException
* if this list contains a null element and the
* specified collection does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>),
* or if the specified collection is null
* @see Collection#contains(Object)
*/
public boolean retainAll (Collection<?> c) {
Objects.requireNonNull (c);
return batchRemove (c, true);
}
/**
* 批量移除
* @param c
* @param complement
* @return
*/
private boolean batchRemove (Collection<?> c, boolean complement) {
final Object[] elementData = this.elementData;
int r = 0, w = 0;
//list是否有修改的标志
boolean modified = false;
try {
//遍历列表，判断每一个元素是否在collection中
//complement==false，list中不包含collection指定位置的数据时，就将list的r位置的数据覆盖掉w位置的数据，
//complement==true，list中包含collection指定位置的数据时，就将list的r位置的数据覆盖掉w位置的数据，
// r位置的数据不变，并其w自增，r自增。
// 否则，r自增，w不自增
//即把不需要移除的元素前移覆盖掉需要移除的元素
for (; r < size; r++)
if (c.contains (elementData[r]) == complement)
elementData[w++] = elementData[r];
} finally {
// Preserve behavioral compatibility with AbstractCollection,
// even if c.contains() throws.
//c.contains()可能抛出异常，要保持与AbstractCollection的行为兼容性，
//r!=size则上面修改都r位置时发生了异常
//把r后续的元素原样前移
if (r != size) {
System.arraycopy (elementData, r,
elementData, w,
size - r);
w += size - r;
}
// 成功删除了元素，将后面空间置空
if (w != size) {
// clear to let GC do its work
for (int i = w; i < size; i++)
elementData[i] = null;
modCount += size - w;
size = w;
modified = true;
}
}
return modified;
}
范围检查
rangeCheck (int index)
rangeCheckForAdd (int index)
outOfBoundsMsg (int index)
/**
* Checks if the given index is in range. If not, throws an appropriate
* runtime exception. This method does *not* check if the index is
* negative: It is always used immediately prior to an array access,
* which throws an ArrayIndexOutOfBoundsException if index is negative.
* 检查index是否超出范围
*/
private void rangeCheck (int index) {
if (index >= size)
throw new IndexOutOfBoundsException (outOfBoundsMsg (index));
}
/**
* A version of rangeCheck used by add and addAll.
* 检查index是否超出范围
*/
private void rangeCheckForAdd (int index) {
//是否够加一个元素
if (index > size || index < 0)
throw new IndexOutOfBoundsException (outOfBoundsMsg (index));
}
/**
* Constructs an IndexOutOfBoundsException detail message.
* 构造IndexOutOfBoundsException详细信息
*
* Of the many possible refactorings of the error handling code,
* this "outlining" performs best with both server and client VMs.
*/
private String outOfBoundsMsg (int index) {
return "Index: " + index + ", Size: " + size;
}
序列化与反序列化
writeObject (java.io.ObjectOutputStream s)
readObject (java.io.ObjectInputStream s)
/**
* Save the state of the <tt>ArrayList</tt> instance to a stream (that
* is, serialize it).
* 把arrayList的状态保存在stream中，也即是序列化
*
*/
private void writeObject (java.io.ObjectOutputStream s)
throws java.io.IOException {
// Write out element count, and any hidden stuff
int expectedModCount = modCount;
s.defaultWriteObject ();
// Write out size as capacity for behavioural compatibility with clone()
//把size写出，当做clone（）方法的容量
s.writeInt (size);
// Write out all elements in the proper order.
//按顺序写出所有元素
for (int i = 0; i < size; i++) {
s.writeObject (elementData[i]);
}
//确保写出过程没有集合被修改，否则报异常
if (modCount != expectedModCount) {
throw new ConcurrentModificationException ();
}
}
/**
* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
* deserialize it).
* 从stream中重建arrayList，也即是反序列化
*/
private void readObject (java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
elementData = EMPTY_ELEMENTDATA;
// Read in size, and any hidden stuff
s.defaultReadObject ();
// Read in capacity
//读取size
s.readInt (); // ignored
if (size > 0) {
// be like clone(), allocate array based upon size not capacity
//与clone()类似，根据大小而不是容量分配数组，如果size大于默认容量则（10）capacity=size，否则capacity=10
int capacity = calculateCapacity (elementData, size);
SharedSecrets.getJavaOISAccess ().checkArray (s, Object[].class, capacity);
ensureCapacityInternal (size);
Object[] a = elementData;
// Read in all elements in the proper order.
for (int i = 0; i < size; i++) {
a[i] = s.readObject ();
}
}
}
listIterator (int index)
listIterator ()
iterator ()
/**
* Returns a list iterator over the elements in this list (in proper
* sequence), starting at the specified position in the list.
* 从指定位置开始顺序返回一个ListIterator
*
* The specified index indicates the first element that would be
* returned by an initial call to {@link ListIterator#next next}.
* 指定的索引暗示着第一次调用 {@link ListIterator#next next}将返回的第一个元素。
*
* An initial call to {@link ListIterator#previous previous} would
* return the element with the specified index minus one.
* 第一次调用 {@link ListIterator#previous previous}将返回的index-1个元素
*
* <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
*
* @throws IndexOutOfBoundsException
* {@inheritDoc}
*/
public ListIterator<E> listIterator (int index) {
if (index < 0 || index > size)
throw new IndexOutOfBoundsException ("Index: " + index);
//创建一个listStr对象（具体看ListItr类注释）
return new ListItr (index);
}
/**
* Returns a list iterator over the elements in this list (in proper
* sequence).
* 返回一个包含list中所有元素的ListIterator
* <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
*
* @see #listIterator(int)
*/
public ListIterator<E> listIterator () {
return new ListItr (0);
}
/**
* Returns an iterator over the elements in this list in proper sequence.
* <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
* 返回一个包含list中所有元素的Iterator
* @return an iterator over the elements in this list in proper sequence
*/
public Iterator<E> iterator () {
return new Itr ();
}
Iterator类
属性
/**
* An optimized version of AbstractList.Itr
* AbstractList.Itr的优化版本
*/
private class Itr implements Iterator<E> {
//游标： 下一个要返回的元素的索引
int cursor; // index of next element to return
//返回的最后一个元素的索引（相当于当前遍历的元素的位置）， 没有就返回-1
int lastRet = - 1; // index of last element returned; -1 if no such
int expectedModCount = modCount;
hasNext ()
/**
* 判断是否还有下一个元素
* @return
*/
public boolean hasNext () {
return cursor != size;
}
next ()
/**
* 获取下一个元素
* @return
*/
@SuppressWarnings ("unchecked")
public E next () {
//检查遍历过程中是否被修改过
checkForComodification ();
//记录索引位置
int i = cursor;
//如果获取元素的位置大于集合元素个数，则抛出异常
if (i >= size)
throw new NoSuchElementException ();
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException ();
//游标后移
cursor = i + 1;
//lastRet记录刚刚返回的位置且返回cursor处元素
return (E) elementData[lastRet = i];
}
remove ()
/**
* 移除最后一元素
*/
public void remove () {
//没有指向的元素
if (lastRet < 0)
throw new IllegalStateException ();
checkForComodification ();
try {
//移除所指向的元素
ArrayList.this.remove (lastRet);
//把游标指向被移除的位置，相当于现在下一个元素的位置
cursor = lastRet;
//当前没有指向的元素（设为-1）
lastRet = - 1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException ();
}
}
forEachRemaining (Consumer<? super E> consumer)
/**
* 遍历剩下的元素，只能用一次
* @param consumer
*/
@Override
@SuppressWarnings ("unchecked")
public void forEachRemaining (Consumer<? super E> consumer) {
//consumer不为空
Objects.requireNonNull (consumer);
final int size = ArrayList.this.size;
//记录索引位置
int i = cursor;
if (i >= size) {
return;
}
final Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length) {
throw new ConcurrentModificationException ();
}
while (i != size && modCount == expectedModCount) {
consumer.accept ((E) elementData[i++]);
}
// update once at end of iteration to reduce heap write traffic
//在迭代结束时才更新，以减少堆写入
cursor = i;
lastRet = i - 1;
checkForComodification ();
}
checkForComodification ()
/**
* 检查是否被修改过
*/
final void checkForComodification () {
if (modCount != expectedModCount)
throw new ConcurrentModificationException ();
}
}
ListItr
/**
* An optimized version of AbstractList.ListItr
* AbstractList.ListItr优化版
*/
private class ListItr extends Itr implements ListIterator<E> {
ListItr (int index) {
super ();
//cursor是当前元素的位置
cursor = index;
}
//是否有前驱（cursor==0代表当前之前第一个位置，所以没有前驱）
public boolean hasPrevious () {
return cursor != 0;
}
//下一个位置
public int nextIndex () {
return cursor;
}
//上一个位置
public int previousIndex () {
return cursor - 1;
}
/**
* 返回上一个位置的元素
* @return
*/
@SuppressWarnings ("unchecked")
public E previous () {
checkForComodification ();
//记录上一个元素的位置
int i = cursor - 1;
if (i < 0)
throw new NoSuchElementException ();
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException ();
//重置cursor为当前元素的位置
cursor = i;
return (E) elementData[lastRet = i];
}
//把当前位置的值重置为e元素
public void set (E e) {
if (lastRet < 0)
throw new IllegalStateException ();
checkForComodification ();
try {
ArrayList.this.set (lastRet, e);
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException ();
}
}
//在遍历的当前位置插入e
public void add (E e) {
checkForComodification ();
try {
int i = cursor;
ArrayList.this.add (i, e);
cursor = i + 1;
lastRet = - 1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException ();
}
}
}
/**
* Returns a view of the portion of this list between the specified
* {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If
* {@code fromIndex} and {@code toIndex} are equal, the returned list is
* empty.)
* 返回从fromIndex到toIndex之间的list
*
* The returned list is backed by this list, so non-structural
* changes in the returned list are reflected in this list, and vice-versa.
* The returned list supports all of the optional list operations.
* <p>This method eliminates the need for explicit range operations (of
* the sort that commonly exist for arrays). Any operation that expects
* a list can be used as a range operation by passing a subList view
* instead of a whole list. For example, the following idiom
* removes a range of elements from a list:
* <pre>
* list.subList(from, to).clear();
* </pre>
* Similar idioms may be constructed for {@link #indexOf(Object)} and
* {@link #lastIndexOf(Object)}, and all of the algorithms in the
* {@link Collections} class can be applied to a subList.
* <p>The semantics of the list returned by this method become undefined if
* the backing list (i.e., this list) is <i>structurally modified</i> in
* any way other than via the returned list. (Structural modifications are
* those that change the size of this list, or otherwise perturb it in such
* a fashion that iterations in progress may yield incorrect results.)
*
* @throws IndexOutOfBoundsException
* {@inheritDoc}
* @throws IllegalArgumentException
* {@inheritDoc}
*/
public List<E> subList (int fromIndex, int toIndex) {
subListRangeCheck (fromIndex, toIndex, size);
return new SubList (this, 0, fromIndex, toIndex);
}
/**
* 检查range合法性
* @param fromIndex
* @param toIndex
* @param size
*/
static void subListRangeCheck (int fromIndex, int toIndex, int size) {
if (fromIndex < 0)
throw new IndexOutOfBoundsException ("fromIndex = " + fromIndex);
if (toIndex > size)
throw new IndexOutOfBoundsException ("toIndex = " + toIndex);
if (fromIndex > toIndex)
throw new IllegalArgumentException ("fromIndex(" + fromIndex +
") > toIndex(" + toIndex + ")");
}
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