ArrayList源码分析
public
class ArrayList<E> extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
//实现Serializable接口,生成的序列版本号:
private
static
final
long
serialVersionUID =
8683452581122892189L
;
//ArrayList初始容量大小:在无参构造中不使用了
private
static
final
int
DEFAULT_CAPACITY =
10
;
//空数组对象:初始化中默认赋值给elementData
private
static
final
Object[] EMPTY_ELEMENTDATA = {};
//ArrayList中实际存储元素的数组:
private
transient
Object[] elementData;
//集合实际存储元素长度:
private
int
size;
//ArrayList有参构造:容量大小
public ArrayList(int initialCapacity)
{
//即父类构造:protected AbstractList() {}空方法
super
();
//如果传递的初始容量小于0 ,抛出异常
if
(initialCapacity <
0
)
throw
new
IllegalArgumentException(
“Illegal Capacity: “
+ initialCapacity);
//初始化数据:创建Object数组
this
.elementData =
new
Object[initialCapacity];
}
//ArrayList无参构造:
public ArrayList()
{
//即父类构造:protected AbstractList() {}空方法
super
();
//初始化数组:空数组,容量为0
this
.elementData = EMPTY_ELEMENTDATA;
}
//ArrayList有参构造:Java集合
public ArrayList(Collection<? extends E> c)
{
//将集合转换为数组:
elementData = c.toArray();
//设置数组的长度:
size = elementData.length;
if
(elementData.getClass() != Object[].class)
elementData = Arrays.copyOf(elementData, size, Object[].class);
}
//将ArrayList的数组大小,变更为实际元素大小:
public void trimToSize()
{
//操作数+1
modCount++;
//如果集合内元素的个数,小于数组的长度,那么将数组中空余元素删除
if
(size < elementData.length) {
elementData = Arrays.copyOf(elementData, size);
}
}
public void ensureCapacity(int minCapacity)
{
int
minExpand = (elementData != EMPTY_ELEMENTDATA) ?
0
: DEFAULT_CAPACITY;
if
(minCapacity > minExpand) {
ensureExplicitCapacity(minCapacity);
}
}
//ArrayList集合内元素的个数:
public int size()
{
return
size;
}
//判断ArrayList集合元素是否为空:
public boolean isEmpty()
{
return
size ==
0
;
}
//判断ArrayList集合包含某个元素:
public boolean contains(Object o)
{
//判断对象o在ArrayList中存在的角标位置
return
indexOf(o) >=
0
;
}
//判断对象o在ArrayList中存在的角标位置:
public int indexOf(Object o)
{
//如果o==null:
if
(o ==
null
) {
//遍历集合,判断哪个元素等于null,则返回对应角标
for
(
int
i =
0
; i < size; i++)
if
(elementData[i]==
null
)
return
i;
}
else
{
//同理:
for
(
int
i =
0
; i < size; i++)
if
(o.equals(elementData[i]))
return
i;
}
//如果不存在,则返回-1
return
–
1
;
}
//判断对象o在ArrayList中出现的最后一个位置:
public int lastIndexOf(Object o)
{
//如果o==null:
if
(o ==
null
) {
//从集合最后一个元素开始遍历:
for
(
int
i = size-
1
; i >=
0
; i–)
if
(elementData[i]==
null
)
return
i;
}
else
{
//同理:
for
(
int
i = size-
1
; i >=
0
; i–)
if
(o.equals(elementData[i]))
return
i;
}
//如果不存在,则返回-1
return
–
1
;
}
//返回此ArrayList实例的 克隆对象:
public Object clone()
{
try
{
java.util.ArrayList<E> v = (java.util.ArrayList<E>)
super
.clone();
v.elementData = Arrays.copyOf(elementData, size);
v.modCount =
0
;
return
v;
}
catch
(CloneNotSupportedException e) {
throw
new
InternalError();
}
}
//将ArrayList里面的元素赋值到一个数组中去 生成Object数组:
public
Object[] toArray() {
return
Arrays.copyOf(elementData, size);
}
//将ArrayList里面的元素赋值到一个数组中去,专成对应类型的数组:
public
<T> T[] toArray(T[] a) {
if
(a.length < size)
return
(T[]) Arrays.copyOf(elementData, size, a.getClass());
System.arraycopy(elementData,
0
, a,
0
, size);
if
(a.length > size)
a[size] =
null
;
return
a;
}
//获取数组index位置的元素:
E elementData(int index)
{
return
(E) elementData[index];
}
//获取index位置的元素
public E get(int index)
{
//检查index是否合法:
rangeCheck(index);
//获取元素:
return
elementData(index);
}
//设置index位置的元素值了element,返回该位置的之前的值
public E set(int index, E element)
{
//检查index是否合法:
rangeCheck(index);
//获取该index原来的元素:
E oldValue = elementData(index);
//替换成新的元素:
elementData[index] = element;
//返回旧的元素:
return
oldValue;
}
//添加元素e
public boolean add(E e)
{
ensureCapacityInternal(size +
1
);
elementData[size++] = e;
return
true
;
}
//在ArrayList的index位置,添加元素element
public void add(int index, E element)
{
//判断index角标的合法性:
rangeCheckForAdd(index);
//判断是否需要扩容:传入当前元素大小+1
ensureCapacityInternal(size +
1
);
System.arraycopy(elementData, index, elementData, index +
1
, size – index);
elementData[index] = element;
size++;
}
//得到最小扩容量
private void ensureCapacityInternal(int minCapacity)
{
//如果此时ArrayList是空数组,则将最小扩容大小设置为10:
if
(elementData == EMPTY_ELEMENTDATA) {
minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
}
//判断是否需要扩容:
ensureExplicitCapacity(minCapacity);
}
//判断是否需要扩容
private void ensureExplicitCapacity(int minCapacity)
{
//操作数+1
modCount++;
//判断最小扩容容量-数组大小是否大于0:
if
(minCapacity – elementData.length >
0
)
//扩容:
grow(minCapacity);
}
//ArrayList最大容量:
private
static
final
int
MAX_ARRAY_SIZE = Integer.MAX_VALUE –
8
;
//帮助ArrayList动态扩容的核心方法:
private void grow(int minCapacity)
{
//获取现有数组大小:
int
oldCapacity = elementData.length;
//位运算,得带新的数组容量大小,为原有的1.5倍:
int
newCapacity = oldCapacity + (oldCapacity >>
1
);
//如果新扩容的大小依旧小于传入的容量值,那么将传入的值设为新容器大小:
if
(newCapacity – minCapacity <
0
)
newCapacity = minCapacity;
//如果新容器大小,大于ArrayList最大长度:
if
(newCapacity – MAX_ARRAY_SIZE >
0
)
//计算出最大容量值:
newCapacity = hugeCapacity(minCapacity);
//数组复制:
elementData = Arrays.copyOf(elementData, newCapacity);
}
//计算ArrayList最大容量:
private static int hugeCapacity(int minCapacity)
{
if
(minCapacity <
0
)
throw
new
OutOfMemoryError();
//如果新的容量大于MAX_ARRAY_SIZE。将会调用hugeCapacity将int的最大值赋给newCapacity:
return
(minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}
//在ArrayList的移除index位置的元素
public E remove(int index)
{
//检查角标是否合法:不合法抛异常
rangeCheck(index);
//操作数+1:
modCount++;
//获取当前角标的value:
E oldValue = elementData(index);
//获取需要删除元素 到最后一个元素的长度,也就是删除元素后,后续元素移动的个数;
int
numMoved = size – index –
1
;
//如果移动元素个数大于0 ,也就是说删除的不是最后一个元素:
if
(numMoved >
0
)
// 将elementData数组index+1位置开始拷贝到elementData从index开始的空间
System.arraycopy(elementData, index+
1
, elementData, index, numMoved);
//size减1,并将最后一个元素置为null
elementData[–size] =
null
;
//返回被删除的元素:
return
oldValue;
}
//在ArrayList的移除对象为O的元素,不返回被删除的元素:
public boolean remove(Object o)
{
//如果o==null,则遍历集合,判断哪个元素为null:
if
(o ==
null
) {
for
(
int
index =
0
; index < size; index++)
if
(elementData[index] ==
null
) {
//快速删除,和前面的remove(index)一样的逻辑
fastRemove(index);
return
true
;
}
}
else
{
//同理:
for
(
int
index =
0
; index < size; index++)
if
(o.equals(elementData[index])) {
fastRemove(index);
return
true
;
}
}
return
false
;
}
//快速删除:
private void fastRemove(int index)
{
//操作数+1
modCount++;
//获取需要删除元素 到最后一个元素的长度,也就是删除元素后,后续元素移动的个数;
int
numMoved = size – index –
1
;
//如果移动元素个数大于0 ,也就是说删除的不是最后一个元素:
if
(numMoved >
0
)
// 将elementData数组index+1位置开始拷贝到elementData从index开始的空间
System.arraycopy(elementData, index+
1
, elementData, index, numMoved);
//size减1,并将最后一个元素置为null
elementData[–size] =
null
;
}
//设置全部元素为null值,并设置size为0。
public void clear()
{
modCount++;
for
(
int
i =
0
; i < size; i++)
elementData[i] =
null
;
size =
0
;
}
//序列化写入:
private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException
{
int
expectedModCount = modCount;
s.defaultWriteObject();
s.writeInt(size);
for
(
int
i=
0
; i<size; i++) {
s.writeObject(elementData[i]);
}
if
(modCount != expectedModCount) {
throw
new
ConcurrentModificationException();
}
}
// 序列化读取:
private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException
{
elementData = EMPTY_ELEMENTDATA;
s.defaultReadObject();
s.readInt();
if
(size >
0
) {
ensureCapacityInternal(size);
Object[] a = elementData;
for
(
int
i=
0
; i<size; i++) {
a[i] = s.readObject();
}
}
}
//检查角标是否合法:不合法抛异常
private void rangeCheck(int index)
{
if
(index >= size)
throw
new
IndexOutOfBoundsException(outOfBoundsMsg(index));
}
//返回一个Iterator对象,Itr为ArrayList的一个内部类,其实现了Iterator<E>接口
public Iterator<E> iterator()
{
return
new
java.util.ArrayList.Itr();
}
//其中的Itr是实现了Iterator接口,同时重写了里面的hasNext(),next(),remove()等方法;
private
class Itr implements Iterator<E>
{
int
cursor;
//类似游标,指向迭代器下一个值的位置
int
lastRet = –
1
;
//迭代器最后一次取出的元素的位置。
int
expectedModCount = modCount;
//Itr初始化时候ArrayList的modCount的值。
//modCount用于记录ArrayList内发生结构性改变的次数,
// 而Itr每次进行next或remove的时候都会去检查expectedModCount值是否还和现在的modCount值,
// 从而保证了迭代器和ArrayList内数据的一致性。
//利用游标,与size之前的比较,判断迭代器是否还有下一个元素
public boolean hasNext()
{
return
cursor != size;
}
//迭代器获取下一个元素:
public E next()
{
//检查modCount是否改变:
checkForComodification();
int
i = cursor;
//游标不会大于等于集合的长度:
if
(i >= size)
throw
new
NoSuchElementException();
Object[] elementData = java.util.ArrayList.
this
.elementData;
//游标不会大于集合中数组的长度:
if
(i >= elementData.length)
throw
new
ConcurrentModificationException();
//游标+1
cursor = i +
1
;
//取出元素:
return
(E) elementData[lastRet = i];
}
public void remove()
{
if
(lastRet <
0
)
throw
new
IllegalStateException();
//检查modCount是否改变:防止并发操作集合
checkForComodification();
try
{
//删除这个元素:
java.util.ArrayList.
this
.remove(lastRet);
//删除后,重置游标,和当前指向元素的角标 lastRet
cursor = lastRet;
lastRet = –
1
;
//重置expectedModCount:
expectedModCount = modCount;
}
catch
(IndexOutOfBoundsException ex) {
throw
new
ConcurrentModificationException();
}
}
//并发检查:在Itr初始化时,将modCount赋值给了expectedModCount
//如果后续modCount还有变化,则抛出异常,所以在迭代器迭代过程中,不能调List增删操作;
final void checkForComodification()
{
if
(modCount != expectedModCount)
throw
new
ConcurrentModificationException();
}
}
}
LinkedList
public class LinkedList<E> extends AbstractSequentialList<E>
implements List<E>, Deque<E>, Cloneable, java.io.Serializable {
//LinkedList的元素个数:
transient int size = 0;
//LinkedList的头结点:Node内部类
transient java.util.LinkedList.Node<E> first;
//LinkedList尾结点:Node内部类
transient java.util.LinkedList.Node<E> last;
//空实现:
public LinkedList() {
}
//调用添加方法:
public LinkedList(Collection<? extends E> c) {
this();
addAll(c);
}
//LinkedList添加首结点 first:
public void addFirst(E e) {
linkFirst(e);
}
//first节点插入新元素:addFirst()调用
private void linkFirst(E e) {
//头结点:
final java.util.LinkedList.Node<E> f = first;
//创建一个新节点,并指向头结点f:
final java.util.LinkedList.Node<E> newNode = new java.util.LinkedList.Node<>(null, e, f);
//将新节点赋值给头几点:
first = newNode;
//如果头节点为null,则是第一个元素插入,将新节点也设置为尾结点;
if (f == null)
last = newNode;
else
//将之前的头结点的前指针指向新的结点:
f.prev = newNode;
//长度+1
size++;
//操作数+1
modCount++;
}
//添加元素:添加到最后一个结点;
public boolean add(E e) {
linkLast(e);
return true;
}
//添加最后一个结点 last:
public void addLast(E e) {
linkLast(e);
}
//last节点插入新元素:addLast()调用
void linkLast(E e) {
//将尾结点赋值个体L:
final java.util.LinkedList.Node<E> l = last;
//创建新的结点,将新节点的前指针指向l:
final java.util.LinkedList.Node<E> newNode = new java.util.LinkedList.Node<>(l, e, null);
//新节点置为尾结点:
last = newNode;
//如果尾结点l为null:则是空集合新插入
if (l == null)
//头结点也置为 新节点:
first = newNode;
else
//l节点的后指针指向新节点:
l.next = newNode;
//长度+1
size++;
//操作数+1
modCount++;
}
//向对应角标添加元素:
public void add(int index, E element) {
//检查传入的角标 是否正确:
checkPositionIndex(index);
//如果插入角标==集合长度,则插入到集合的最后面:
if (index == size)
linkLast(element);
else
//插入到对应角标的位置:获取此角标下的元素先
linkBefore(element, node(index));
}
//在succ前插入 新元素e:
void linkBefore(E e, java.util.LinkedList.Node<E> succ) {
//获取被插入元素succ的前指针元素:
final java.util.LinkedList.Node<E> pred = succ.prev;
//创建新增元素节点,前指针 和 后指针分别指向对应元素:
final java.util.LinkedList.Node<E> newNode = new java.util.LinkedList.Node<>(pred, e, succ);
succ.prev = newNode;
//succ的前指针元素可能为null,为null的话说明succ是头结点,则把新建立的结点置为头结点:
if (pred == null)
first = newNode;
else
//succ前指针不为null,则将前指针的结点的后指针指向新节点:
pred.next = newNode;
//长度+1
size++;
//操作数+1
modCount++;
}
//移除首个结点:如果集合还没有元素则报错
public E removeFirst() {
final java.util.LinkedList.Node<E> f = first;
//首节点为null,则抛出异常;
if (f == null)
throw new NoSuchElementException();
return unlinkFirst(f);
}
//删除LinkedList的头结点:removeFirst()方法调用
private E unlinkFirst(java.util.LinkedList.Node<E> f) {
//f为头结点:获取头结点元素E
final E element = f.item;
//获取头结点的尾指针结点:
final java.util.LinkedList.Node<E> next = f.next;
//将头结点元素置为null:
f.item = null;
//头结点尾指针置为null:
f.next = null;
//将头结点的尾指针指向的结点next置为first
first = next;
//尾指针指向结点next为null的话,就将尾结点也置为null(LinkedList中只有一个元素时出现)
if (next == null)
last = null;
else
//将尾指针指向结点next的 前指针置为null;
next.prev = null;
// 长度减1
size–;
//操作数+1
modCount++;
//返回被删除的元素:
return element;
}
//移除最后一个结点:如果集合还没有元素则报错
public E removeLast() {
//获取最后一个结点:
final java.util.LinkedList.Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
//删除尾结点:
return unlinkLast(l);
}
//删除LinkedList的尾结点:removeLast()方法调用
private E unlinkLast(java.util.LinkedList.Node<E> l) {
final E element = l.item;
final java.util.LinkedList.Node<E> prev = l.prev;
l.item = null;
l.prev = null; // help GC
last = prev;
if (prev == null)
first = null;
else
prev.next = null;
size–;
modCount++;
return element;
}
//删除LinkedList中的元素,可以删除为null的元素,逐个遍历LinkedList的元素;
//重复元素只删除第一个:
public boolean remove(Object o) {
//如果删除元素为null:
if (o == null) {
for (java.util.LinkedList.Node<E> x = first; x != null; x = x.next) {
if (x.item == null) {
unlink(x);
return true;
}
}
} else {
//如果删除元素不为null:
for (java.util.LinkedList.Node<E> x = first; x != null; x = x.next) {
if (o.equals(x.item)) {
unlink(x);
return true;
}
}
}
return false;
}
//移除LinkedList结点:remove()方法中调用
E unlink(java.util.LinkedList.Node<E> x) {
//获取被删除结点的元素E:
final E element = x.item;
//获取被删除元素的后指针结点:
final java.util.LinkedList.Node<E> next = x.next;
//获取被删除元素的前指针结点:
final java.util.LinkedList.Node<E> prev = x.prev;
//被删除结点的 前结点为null的话:
if (prev == null) {
//将后指针指向的结点置为头结点
first = next;
} else {
//前置结点的 尾结点指向被删除的next结点;
prev.next = next;
//被删除结点前指针置为null:
x.prev = null;
}
//对尾结点同样处理:
if (next == null) {
last = prev;
} else {
next.prev = prev;
x.next = null;
}
x.item = null;
size–;
modCount++;
return element;
}
//得到首个结点:集合没有元素报错
public E getFirst() {
//获取first结点:
final java.util.LinkedList.Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return f.item;
}
//得到最后一个结点:集合没有元素报错
public E getLast() {
//获取last结点:
final java.util.LinkedList.Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return l.item;
}
//判断obj 是否存在:
public boolean contains(Object o) {
return indexOf(o) != –1;
}
//LinkedList长度:
public int size() {
return size;
}
//添加集合:从最后size所在的index开始:
public boolean addAll(Collection<? extends E> c) {
return addAll(size, c);
}
//LinkedList添加集合:
public boolean addAll(int index, Collection<? extends E> c) {
//检查角标是否正确:
checkPositionIndex(index);
Object[] a = c.toArray();
int numNew = a.length;
if (numNew == 0)
return false;
java.util.LinkedList.Node<E> pred, succ;
if (index == size) {
succ = null;
pred = last;
} else {
succ = node(index);
pred = succ.prev;
}
for (Object o : a) {
E e = (E) o;
java.util.LinkedList.Node<E> newNode = new java.util.LinkedList.Node<>(pred, e, null);
if (pred == null)
first = newNode;
else
pred.next = newNode;
pred = newNode;
}
if (succ == null) {
last = pred;
} else {
pred.next = succ;
succ.prev = pred;
}
size += numNew;
modCount++;
return true;
}
//清空LinkedList:
public void clear() {
//遍历LinedList集合:
for (java.util.LinkedList.Node<E> x = first; x != null; ) {
//将每个结点的前指针 尾指针 元素都置为null:
java.util.LinkedList.Node<E> next = x.next;
x.item = null;
x.next = null;
x.prev = null;
x = next;
}
//头尾结点 都置为null:
first = last = null;
//长度置为0
size = 0;
//操作数+1:
modCount++;
}
//获取相应角标的元素:
public E get(int index) {
//检查角标是否正确:
checkElementIndex(index);
//获取角标所属结点的 元素值:
return node(index).item;
}
//设置对应角标的元素:
public E set(int index, E element) {
checkElementIndex(index);
java.util.LinkedList.Node<E> x = node(index);
E oldVal = x.item;
x.item = element;
return oldVal;
}
//删除对应角标的元素:
public E remove(int index) {
checkElementIndex(index);
return unlink(node(index));
}
//获取对应角标所属于的结点:
java.util.LinkedList.Node<E> node(int index) {
//位运算:如果位置索引小于列表长度的一半,从前面开始遍历;否则,从后面开始遍历;
if (index < (size >> 1)) {
java.util.LinkedList.Node<E> x = first;
//从头结点开始遍历:遍历的长度就是index的长度,获取对应的index的元素
for (int i = 0; i < index; i++)
x = x.next;
return x;
} else {
//从集合尾结点遍历:
java.util.LinkedList.Node<E> x = last;
//同样道理:
for (int i = size – 1; i > index; i–)
x = x.prev;
return x;
}
}
// 左移相当于*2,只是要注意边界问题。如char a = 65; a<<1 按照*2来算为130;
// 但有符号char的取值范围-128~127,已经越界,多超出了3个数值,
// 所以从-128算起的第三个数值-126才是a<<1的正确结果。
//而右移相当于除以2,只是要注意移位比较多的时候结果会趋近去一个非常小的数,如上面结果中的-1,0。
private boolean isElementIndex(int index) {
return index >= 0 && index < size;
}
//判断传入的index是否正确:
private boolean isPositionIndex(int index) {
return index >= 0 && index <= size;
}
private String outOfBoundsMsg(int index) {
return “Index: “+index+“, Size: “+size;
}
private void checkElementIndex(int index) {
if (!isElementIndex(index))
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
//检查传入的角标 是否正确:
private void checkPositionIndex(int index) {
//必须大于0 ,并且不能大于当前size:
if (!isPositionIndex(index))
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
public int indexOf(Object o) {
int index = 0;
if (o == null) {
for (java.util.LinkedList.Node<E> x = first; x != null; x = x.next) {
if (x.item == null)
return index;
index++;
}
} else {
for (java.util.LinkedList.Node<E> x = first; x != null; x = x.next) {
if (o.equals(x.item))
return index;
index++;
}
}
return –1;
}
public int lastIndexOf(Object o) {
int index = size;
if (o == null) {
for (java.util.LinkedList.Node<E> x = last; x != null; x = x.prev) {
index–;
if (x.item == null)
return index;
}
} else {
for (java.util.LinkedList.Node<E> x = last; x != null; x = x.prev) {
index–;
if (o.equals(x.item))
return index;
}
}
return –1;
}
//获取第一个元素,不存在则抛异常
public E element() {
return getFirst();
}
//出队,获取第一个元素,不出队列,只是获取
// 队列先进先出;不存在不抛异常,返回null
public E peek() {
//获取头结点:
final java.util.LinkedList.Node<E> f = first;
//存在获取头结点元素,不存在返回null
return (f == null) ? null : f.item;
}
//出队,并移除第一个元素;不存在不抛异常。
public E poll() {
final java.util.LinkedList.Node<E> f = first;
return (f == null) ? null : unlinkFirst(f);
}
//出队(删除第一个结点),如果不存在会抛出异常而不是返回null,存在的话会返回值并移除这个元素(节点)
public E remove() {
return removeFirst();
}
//入队(插入最后一个结点)从最后一个元素
public boolean offer(E e) {
return add(e);
}
//入队(插入头结点),始终返回true
public boolean offerFirst(E e) {
addFirst(e);
return true;
}
//入队(插入尾结点),始终返回true
public boolean offerLast(E e) {
addLast(e);
return true;
}
//出队(从前端),获得第一个元素,不存在会返回null,不会删除元素(节点)
public E peekFirst() {
final java.util.LinkedList.Node<E> f = first;
return (f == null) ? null : f.item;
}
//出队(从后端),获得最后一个元素,不存在会返回null,不会删除元素(节点)
public E peekLast() {
final java.util.LinkedList.Node<E> l = last;
return (l == null) ? null : l.item;
}
//出队(从前端),获得第一个元素,不存在会返回null,会删除元素(节点)
public E pollFirst() {
final java.util.LinkedList.Node<E> f = first;
return (f == null) ? null : unlinkFirst(f);
}
//出队(从后端),获得最后一个元素,不存在会返回null,会删除元素(节点)
public E pollLast() {
final java.util.LinkedList.Node<E> l = last;
return (l == null) ? null : unlinkLast(l);
}
//入栈,从前面添加 栈 后进先出
public void push(E e) {
addFirst(e);
}
//出栈,返回栈顶元素,从前面移除(会删除)
public E pop() {
return removeFirst();
}
//节点的数据结构,包含前后节点的引用和当前节点
private static class Node<E> {
//结点元素:
E item;
//结点后指针
java.util.LinkedList.Node<E> next;
//结点前指针
java.util.LinkedList.Node<E> prev;
Node(java.util.LinkedList.Node<E> prev, E element, java.util.LinkedList.Node<E> next) {
this.item = element;
this.next = next;
this.prev = prev;
}
}
//迭代器:
public ListIterator<E> listIterator(int index) {
checkPositionIndex(index);
return new java.util.LinkedList.ListItr(index);
}
private class ListItr implements ListIterator<E> {
private java.util.LinkedList.Node<E> lastReturned = null;
private java.util.LinkedList.Node<E> next;
private int nextIndex;
private int expectedModCount = modCount;
ListItr(int index) {
next = (index == size) ? null : node(index);
nextIndex = index;
}
public boolean hasNext() {
return nextIndex < size;
}
public E next() {
checkForComodification();
if (!hasNext())
throw new NoSuchElementException();
lastReturned = next;
next = next.next;
nextIndex++;
return lastReturned.item;
}
public boolean hasPrevious() {
return nextIndex > 0;
}
public E previous() {
checkForComodification();
if (!hasPrevious())
throw new NoSuchElementException();
lastReturned = next = (next == null) ? last : next.prev;
nextIndex–;
return lastReturned.item;
}
public int nextIndex() {
return nextIndex;
}
public int previousIndex() {
return nextIndex – 1;
}
public void remove() {
checkForComodification();
if (lastReturned == null)
throw new IllegalStateException();
java.util.LinkedList.Node<E> lastNext = lastReturned.next;
unlink(lastReturned);
if (next == lastReturned)
next = lastNext;
else
nextIndex–;
lastReturned = null;
expectedModCount++;
}
public void set(E e) {
if (lastReturned == null)
throw new IllegalStateException();
checkForComodification();
lastReturned.item = e;
}
public void add(E e) {
checkForComodification();
lastReturned = null;
if (next == null)
linkLast(e);
else
linkBefore(e, next);
nextIndex++;
expectedModCount++;
}
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
private java.util.LinkedList<E> superClone() {
try {
return (java.util.LinkedList<E>) super.clone();
} catch (CloneNotSupportedException e) {
throw new InternalError();
}
}
public Object clone() {
java.util.LinkedList<E> clone = superClone();
clone.first = clone.last = null;
clone.size = 0;
clone.modCount = 0;
for (java.util.LinkedList.Node<E> x = first; x != null; x = x.next)
clone.add(x.item);
return clone;
}
public Object[] toArray() {
Object[] result = new Object[size];
int i = 0;
for (java.util.LinkedList.Node<E> x = first; x != null; x = x.next)
result[i++] = x.item;
return result;
}
@SuppressWarnings(“unchecked”)
public <T> T[] toArray(T[] a) {
if (a.length < size)
a = (T[])java.lang.reflect.Array.newInstance(
a.getClass().getComponentType(), size);
int i = 0;
Object[] result = a;
for (java.util.LinkedList.Node<E> x = first; x != null; x = x.next)
result[i++] = x.item;
if (a.length > size)
a[size] = null;
return a;
}
private static final long serialVersionUID = 876323262645176354L;
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
s.defaultWriteObject();
s.writeInt(size);
for (java.util.LinkedList.Node<E> x = first; x != null; x = x.next)
s.writeObject(x.item);
}
@SuppressWarnings(“unchecked”)
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
s.defaultReadObject();
int size = s.readInt();
for (int i = 0; i < size; i++)
linkLast((E)s.readObject());
}
}