【java】LinkedList源码分析(JDK1.8)
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2022-03-04 11:21:26
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文章目录
LinkedList简述
LinkedList是底层由双向链表实现的动态数组类。它继承AbstractSequentialList类，实现List、Deque、Cloneable和Serializable接口。
public class LinkedList<E>
extends AbstractSequentialList<E>
implements List<E>, Deque<E>, Cloneable, java.io.Serializable
{
LinkedList属性
表示节点的内部类
private static class Node<E> {
E item;
Node<E> next;
Node<E> prev;
Node(Node<E> prev, E element, Node<E> next) {
this.item = element;
this.next = next;
this.prev = prev;
}
}
链表长度
transient int size = 0;
头节点和尾节点
transient Node<E> first;
transient Node<E> last;
modCount记录修改的次数
LinkedList构造方法
无参构造方法
返回一个空链表，first节点也为空
public LinkedList() {
}
带Collectioin参数的构造方法
这里this()为调用本类中另一种形式的构造方法，在这里就是指无参构造方法，addAll方法在下面添加方法里。
public LinkedList(Collection<? extends E> c) {
this();
addAll(c);
}
LinkedList主要方法
增删改查
由于LinkedList实现了Deque，而Deque接口定义了在双端队列两端访问元素的方法。提供插入、移除和检查元素的方法。每种方法都存在两种形式：一种形式在操作失败时抛出异常，另一种形式返回一个特殊值。这里只列出抛出异常的形式，因为其原理都是一致的。
增加
在末尾增加一个数据域值为e的节点
public void addLast(E e) {
linkLast(e);
}
void linkLast(E e) {
final Node<E> l = last;
final Node<E> newNode = new Node<>(l, e, null);
last = newNode;
if (l == null)
first = newNode;
else
l.next = newNode;
size++;
modCount++;
}
在指定元素succ前增加一个数据域值为e的节点
void linkBefore(E e, Node<E> succ) {
// assert succ != null;
final Node<E> pred = succ.prev;
final Node<E> newNode = new Node<>(pred, e, succ);
succ.prev = newNode;
if (pred == null)
first = newNode;
else
pred.next = newNode;
size++;
modCount++;
}
添加一个数据域值为e的节点为当前链表的头节点
public void addFirst(E e) {
linkFirst(e);
}
private void linkFirst(E e) {
final Node<E> f = first;
final Node<E> newNode = new Node<>(null, e, f);
first = newNode;
if (f == null)
last = newNode;
else
f.prev = newNode;
size++;
modCount++;
}
添加collection c里所有对象到index之后。
public boolean addAll(Collection<? extends E> c) {
return addAll(size, c);
}
public boolean addAll(int index, Collection<? extends E> c) {
checkPositionIndex(index);
Object[] a = c.toArray();
int numNew = a.length;
if (numNew == 0)
return false;
Node<E> 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<E> 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;
}
删除
删除头节点、删除尾节点。删除操作是将要删除节点的数据域和指针域都置为空，等待gc来回收。返回被删除节点数据域里的值。
public E removeFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return unlinkFirst(f);
}
public E removeLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return unlinkLast(l);
}
private E unlinkLast(Node<E> l) {
// assert l == last && l != null;
final E element = l.item;
final 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;
}
删除数据域值为o的节点，若有多个数据域值相同的节点，只删除第一个。
public boolean remove(Object o) {
if (o == null) {
for (Node<E> x = first; x != null; x = x.next) {
if (x.item == null) {
unlink(x);
return true;
}
}
} else {
for (Node<E> x = first; x != null; x = x.next) {
if (o.equals(x.item)) {
unlink(x);
return true;
}
}
}
return false;
}
修改
找到要修改的节点，修改，返回修改前的值。
public E set(int index, E element) {
checkElementIndex(index);
Node<E> x = node(index);
E oldVal = x.item;
x.item = element;
return oldVal;
}
查询
查询头节点、尾节点
public E getFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return f.item;
}
public E getLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return l.item;
}
查询第index个节点，这里node方法采用了二分法的思想，遍历链表前先判断index在前半段还是后半段中，在前半段则从头结点往后遍历，在后半段则从尾节点向前遍历，提高了查找效率。
public E get(int index) {
checkElementIndex(index);
return node(index).item;
}
Node<E> node(int index) {
// assert isElementIndex(index);
if (index < (size >> 1)) {
Node<E> x = first;
for (int i = 0; i < index; i++)
x = x.next;
return x;
} else {
Node<E> x = last;
for (int i = size - 1; i > index; i--)
x = x.prev;
return x;
}
}
查询头结点的值
public E peek() {
final Node<E> f = first;
return (f == null) ? null : f.item;
}
查询数据域值为o的节点，若有多个，只查到第一个。
public int indexOf(Object o) {
int index = 0;
if (o == null) {
for (Node<E> x = first; x != null; x = x.next) {
if (x.item == null)
return index;
index++;
}
} else {
for (Node<E> x = first; x != null; x = x.next) {
if (o.equals(x.item))
return index;
index++;
}
}
return -1;
}
查询数据域值为o的节点，若有多个，只查最后一个
public int lastIndexOf(Object o) {
int index = size;
if (o == null) {
for (Node<E> x = last; x != null; x = x.prev) {
index--;
if (x.item == null)
return index;
}
} else {
for (Node<E> x = last; x != null; x = x.prev) {
index--;
if (o.equals(x.item))
return index;
}
}
return -1;
}
clear方法
将链表清空，就是全部节点的数据域指针域都置为null
public void clear() {
// Clearing all of the links between nodes is "unnecessary", but:
// - helps a generational GC if the discarded nodes inhabit
// more than one generation
// - is sure to free memory even if there is a reachable Iterator
for (Node<E> x = first; x != null; ) {
Node<E> next = x.next;
x.item = null;
x.next = null;
x.prev = null;
x = next;
}
first = last = null;
size = 0;
modCount++;
}
clone方法
复制链表为一个新链表，返回新链表
public Object clone() {
LinkedList<E> clone = superClone();
// Put clone into "virgin" state
clone.first = clone.last = null;
clone.size = 0;
clone.modCount = 0;
// Initialize clone with our elements
for (Node<E> x = first; x != null; x = x.next)
clone.add(x.item);
return clone;
}
toArray、size等方法很简单，就不一一写了
总结
1.LinkedList底层为双向链表，有一个内部类Node作为链表的基本单位。
2.LinkedList实现了迭代器、Serializable可接口。