LinkedList简介
LinkedList简介
LinkedList简介
LinkedList除了可以当做链表来操作外，它还可以当做栈、队列和双端队列来使用。
LinkedList同样是非线程安全的，只在单线程下适合使用。
LinkedList实现了Serializable接口，因此它支持序列化，能够通过序列化传输，实现了Cloneable接口，能被克隆。
LinkedList源码剖析
public class LinkedList
extends AbstractSequentialList
implements List, Deque, Cloneable, java.io.Serializable
{
// LinkedList中元素个数
transient int size = 0;
//链表的头节点
transient Node first;
//链表的尾节点
transient Node last;
// 默认构造函数
public LinkedList() {
}
// 包含“集合”的构造函数:创建一个包含“集合”的LinkedList
public LinkedList(Collection c) {
this();
addAll(c);
}
//把e链接为链表的头节点
private void linkFirst(E e) {
final Node f = first;
final Node newNode = new Node<>(null, e, f);
first = newNode;
if (f == null)
last = newNode;
else
f.prev = newNode;
size++;
modCount++;
}
//把e链接为链表的尾节点
void linkLast(E e) {
final Node l = last;
final Node newNode = new Node<>(l, e, null);
last = newNode;
if (l == null)
first = newNode;
else
l.next = newNode;
size++;
modCount++;
}
//在指定节点前插入e
void linkBefore(E e, Node succ) {
// assert succ != null;
final Node pred = succ.prev;
final Node newNode = new Node<>(pred, e, succ);
succ.prev = newNode;
if (pred == null)
first = newNode;
else
pred.next = newNode;
size++;
modCount++;
}
//删除头部元素f
private E unlinkFirst(Node f) {
// assert f == first && f != null;
final E element = f.item;
final Node next = f.next;
f.item = null;
f.next = null; // help GC
first = next;
if (next == null)
last = null;
else
next.prev = null;
size--;
modCount++;
return element;
}
//删除尾部元素l
private E unlinkLast(Node l) {
// assert l == last && l != null;
final E element = l.item;
final Node 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;
}
//删除节点x
E unlink(Node x) {
// assert x != null;
final E element = x.item;
final Node next = x.next;
final Node prev = x.prev;
if (prev == null) {
first = next;
} else {
prev.next = next;
x.prev = null;
}
if (next == null) {
last = prev;
} else {
next.prev = prev;
x.next = null;
}
x.item = null;
size--;
modCount++;
return element;
}
// 返回第一个节点
public E getFirst() {
final Node f = first;
if (f == null)
throw new NoSuchElementException();
return f.item;
}
// 返回最后一个节点
public E getLast() {
final Node l = last;
if (l == null)
throw new NoSuchElementException();
return l.item;
}
// 删除头部节点
public E removeFirst() {
final Node f = first;
if (f == null)
throw new NoSuchElementException();
return unlinkFirst(f);
}
// 删除尾部节点
public E removeLast() {
final Node l = last;
if (l == null)
throw new NoSuchElementException();
return unlinkLast(l);
}
//在头部添加“e”
public void addFirst(E e) {
linkFirst(e);
}
//在尾部添加“e”
public void addLast(E e) {
linkLast(e);
}
//判断是否包含“o”
public boolean contains(Object o) {
return indexOf(o) != -1;
}
//返回元素个数
public int size() {
return size;
}
//在尾部添加“e”
public boolean add(E e) {
linkLast(e);
return true;
}
// 删除节点"o"
public boolean remove(Object o) {
if (o == null) {
for (Node x = first; x != null; x = x.next) {
if (x.item == null) {
unlink(x);
return true;
}
}
} else {
for (Node x = first; x != null; x = x.next) {
if (o.equals(x.item)) {
unlink(x);
return true;
}
}
}
return false;
}
// 将“集合(c)”添加到链表中。
public boolean addAll(Collection c) {
return addAll(size, c);
}
// 从链表的index开始，将“集合(c)”添加到链表中。
public boolean addAll(int index, Collection c) {
checkPositionIndex(index);
Object[] a = c.toArray();
int numNew = a.length;
if (numNew == 0)
return false;
Node pred, succ;
if (index == size) {
succ = null;
pred = last;
} else {
succ = node(index);
pred = succ.prev;
}
for (Object o : a) {
@SuppressWarnings("unchecked") E e = (E) o;
Node newNode = new 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;
}
// 清空链表
public void clear() {
// 从表头开始，逐个向后遍历；对遍历到的节点执行一下操作：
// (01) 设置前一个节点为null
// (02) 设置当前节点的内容为null
// (03) 设置后一个节点为“新的当前节点”
for (Node x = first; x != null; ) {
Node next = x.next;
x.item = null;
x.next = null;
x.prev = null;
x = next;
}
first = last = null;
size = 0;
modCount++;
}
// Positional Access Operations
// 返回LinkedList指定位置的元素
public E get(int index) {
checkElementIndex(index);
return node(index).item;
}
// 设置index位置对应的节点的值为element
public E set(int index, E element) {
checkElementIndex(index);
Node x = node(index);
E oldVal = x.item;
x.item = element;
return oldVal;
}
// 在index前添加节点，且节点的值为element
public void add(int index, E element) {
checkPositionIndex(index);
if (index == size)
linkLast(element);
else
linkBefore(element, node(index));
}
// 删除index位置的节点
public E remove(int index) {
checkElementIndex(index);
return unlink(node(index));
}
//判断index位置是否存在节点
private boolean isElementIndex(int index) {
return index >= 0 && index < size;
}
//判断index位置是否存在节点以及是否可以在该位置添加节点
private boolean isPositionIndex(int index) {
return index >= 0 && index <= size;
}
/**
* Constructs an IndexOutOfBoundsException detail message.
* 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;
}
//检查是否越界
private void checkElementIndex(int index) {
if (!isElementIndex(index))
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
//检查是否越界
private void checkPositionIndex(int index) {
if (!isPositionIndex(index))
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
/**
* Returns the (non-null) Node at the specified element index.
*/
Node node(int index) {
// assert isElementIndex(index);
if (index < (size >> 1)) {
Node x = first;
for (int i = 0; i < index; i++)
x = x.next;
return x;
} else {
Node x = last;
for (int i = size - 1; i > index; i--)
x = x.prev;
return x;
}
}
// Search Operations
// 从前向后查找，返回“值为对象(o)的节点对应的索引”
// 不存在就返回-1
public int indexOf(Object o) {
int index = 0;
if (o == null) {
for (Node x = first; x != null; x = x.next) {
if (x.item == null)
return index;
index++;
}
} else {
for (Node x = first; x != null; x = x.next) {
if (o.equals(x.item))
return index;
index++;
}
}
return -1;
}
// 从后向前查找，返回“值为对象(o)的节点对应的索引”
// 不存在就返回-1
public int lastIndexOf(Object o) {
int index = size;
if (o == null) {
for (Node x = last; x != null; x = x.prev) {
index--;
if (x.item == null)
return index;
}
} else {
for (Node x = last; x != null; x = x.prev) {
index--;
if (o.equals(x.item))
return index;
}
}
return -1;
}
// Queue operations.
// 获取第一个链表节点的值，判断是否为空，不为空则返回节点对应的值。
public E peek() {
final Node f = first;
return (f == null) ? null : f.item;
}
//返回第一个节点的值。
public E element() {
return getFirst();
}
//删除链表的首节点；如果节点不为空就调用unlinkFirst(Node)方法，做的事情很简单，
//删除首节点，垃圾回收还有就是更新链表长度。
public E poll() {
final Node f = first;
return (f == null) ? null : unlinkFirst(f);
}
public E remove() {
return removeFirst();
}
//将元素添加到链表的末尾；
public boolean offer(E e) {
return add(e);
}
//将元素添加到元素首部
public boolean offerFirst(E e) {
addFirst(e);
return true;
}
//将元素添加到链表的末尾；
public boolean offerLast(E e) {
addLast(e);
return true;
}
// 返回第一个节点 若LinkedList的大小为0,则返回null
public E peekFirst() {
final Node f = first;
return (f == null) ? null : f.item;
}
// 返回最后一个节点，若LinkedList的大小为0,则返回null
public E peekLast() {
final Node l = last;
return (l == null) ? null : l.item;
}
// 删除并返回第一个节点，若LinkedList的大小为0,则返回null
public E pollFirst() {
final Node f = first;
return (f == null) ? null : unlinkFirst(f);
}
// 删除并返回最后一个节点
// 若LinkedList的大小为0,则返回null
public E pollLast() {
final Node l = last;
return (l == null) ? null : unlinkLast(l);
}
//将元素插入到头部，
public void push(E e) {
addFirst(e);
}
//将第一个元素删除，头部节点，
public E pop() {
return removeFirst();
}
// 从LinkedList开始向后查找，删除第一个值为元素(o)的节点
public boolean removeFirstOccurrence(Object o) {
return remove(o);
}
// 从LinkedList末尾向前查找，删除第一个值为元素(o)的节点
public boolean removeLastOccurrence(Object o) {
if (o == null) {
for (Node x = last; x != null; x = x.prev) {
if (x.item == null) {
unlink(x);
return true;
}
}
} else {
for (Node x = last; x != null; x = x.prev) {
if (o.equals(x.item)) {
unlink(x);
return true;
}
}
}
return false;
}
// 返回“index到末尾的全部节点”对应的ListIterator对象(List迭代器)
public ListIterator listIterator(int index) {
checkPositionIndex(index);
return new ListItr(index);
}
参考资料：http://blog.csdn.net/ns_code/article/details/35787253以及jdk 1.8