LinkedList源码解析
Posted 夜宿山寺
tags:
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后面的大多数方法其实跟ArrayList的差不多，就不做过多解释了
package java.util;
import java.util.function.Consumer;
/*
所有已实现的接口：
Serializable, Cloneable, Iterable<E>, Collection<E>, Deque<E>, List<E>, Queue<E>
List 接口的链接列表实现。实现所有可选的列表操作，并且允许所有元素（包括 null）。除了实现 List 接口外，LinkedList
类还为在列表的开头及结尾 get、remove 和 insert 元素提供了统一的命名方法。这些操作允许将链接列表用作堆栈、队列或双端队列。
此类实现 Deque 接口，为 add、poll 提供先进先出队列操作，以及其他堆栈和双端队列操作。
所有操作都是按照双重链接列表的需要执行的。在列表中编索引的操作将从开头或结尾遍历列表（从靠近指定索引的一端）。
*/
public class LinkedList<E>
extends AbstractSequentialList<E>
implements List<E>, Deque<E>, Cloneable, java.io.Serializable
//当前节点数量
transient int size = 0;
/**
* Pointer to first node.
* Invariant: (first == null && last == null) ||
* (first.prev == null && first.item != null)
*/
//节点首部
transient Node<E> first;
/**
* Pointer to last node.
* Invariant: (first == null && last == null) ||
* (last.next == null && last.item != null)
*/
//节点尾部
transient Node<E> last;
public LinkedList()
public LinkedList(Collection<? extends E> c)
this();
addAll(c);
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++;
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++;
/**
* Inserts element e before non-null Node succ.
*/
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++;
/**
* Unlinks non-null first node f.
*/
//移除首部节点具体实现
private E unlinkFirst(Node<E> f)
// assert f == first && f != null;
final E element = f.item;
final Node<E> 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;
//移除尾部节点
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;
//移除节点
E unlink(Node<E> x)
// assert x != null;
final E element = x.item;
//将前后指针的地址付给两个节点
final Node<E> next = x.next;
final Node<E> 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;
//获取首部节点
public E getFirst()
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return f.item;
//获取尾部节点
public E getLast()
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return l.item;
//移除首部节点
public E removeFirst()
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return unlinkFirst(f);
//发布出来的公共方法，移除尾部节点
public E removeLast()
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return unlinkLast(l);
//添加首部节点
public void addFirst(E e)
linkFirst(e);
//添加到尾部
public void addLast(E e)
linkLast(e);
/**
* Returns @code true if this list contains the specified element.
* More formally, returns @code true if and only if this list contains
* at least one element @code e such that
* <tt>(o==null ? e==null : o.equals(e))</tt>.
*
* @param o element whose presence in this list is to be tested
* @return @code true if this list contains the specified element
*/
public boolean contains(Object o)
return indexOf(o) != -1;
/**
* Returns the number of elements in this list.
*
* @return the number of elements in this list
*/
public int size()
return size;
//默认添加节点是从尾部进行添加的
public boolean add(E e)
linkLast(e);
return true;
//移除节点，最好复写该对象的equals方法
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;
//添加集合里面的全部节点
public boolean addAll(Collection<? extends E> c)
return addAll(size, c);
//指定index添加节点
public boolean addAll(int index, Collection<? extends E> c)
//检测是否越界
checkPositionIndex(index);
//转换成对象数组
Object[] a = c.toArray();
int numNew = a.length;
if (numNew == 0)
return false;
Node<E> pred, succ;
//如果是从尾部开始添加就把当前尾部的节点地址给新节点的前驱
if (index == size)
succ = null;
pred = last;
else
//否则就获取index节点 把index节点的前驱地址给pred
succ = node(index);
pred = succ.prev;
//遍历对象数组
for (Object o : a)
@SuppressWarnings("unchecked") E e = (E) o;
//创建新节点
Node<E> newNode = new Node<>(pred, e, null);
//判断前驱节点是否存在，不存在则把当前节点设置为头部节点，存在则把pred节点的下一个指向地址指向新节点
if (pred == null)
first = newNode;
else
pred.next = newNode;
pred = newNode;
//尾节点是否为null 如果为null则把添加进来的最后一个节点设置为尾节点
//如果不为null则把pred节点的下一个节点指向succ
if (succ == null)
last = pred;
else
pred.next = succ;
succ.prev = pred;
size += numNew;
modCount++;
return true;
//清除所有节点
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++;
//提供随机访问节点方法
public E get(int index)
checkElementIndex(index);
return node(index).item;
//这些都是数据结构常用的方法我就不多说了
public E set(int index, E element)
checkElementIndex(index);
Node<E> x = node(index);
E oldVal = x.item;
x.item = element;
return oldVal;
public void add(int index, E element)
checkPositionIndex(index);
if (index == size)
linkLast(element);
else
linkBefore(element, node(index));
public E remove(int index)
checkElementIndex(index);
return unlink(node(index));
private boolean isElementIndex(int index)
return index >= 0 && index < size;
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));
private void checkPositionIndex(int index)
if (!isPositionIndex(index))
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
//遍历节点提供随机访问
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;
// Search Operations
//这两个方法和ArrayList提供的其实没有多大差别，都是遍历
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;
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;
// Queue operations.
//这个方法是1.5之后提供的 获取表头元素 不移除
public E peek()
final Node<E> f = first;
return (f == null) ? null : f.item;
// 获取但不移除此列表的头
public E element()
return getFirst();
// 获取并移除此列表的头
public E poll()
final Node<E> f = first;
return (f == null) ? null : unlinkFirst(f);
//获取并移除此列表的头（第一个元素）。
public E remove()
return removeFirst();
/**
* Adds the specified element as the tail (last element) of this list.
*
* @param e the element to add
* @return @code true (as specified by @link Queue#offer)
* @since 1.5
*/
//实现队列的offer方法 将指定元素添加到此列表的末尾
public boolean offer(E e)
return add(e);
// Deque operations
/**
* Inserts the specified element at the front of this list.
*
* @param e the element to insert
* @return @code true (as specified by @link Deque#offerFirst)
* @since 1.6
*/
//在此列表的开头插入指定的元素。
public boolean offerFirst(E e)
addFirst(e);
return true;
/**
* Inserts the specified element at the end of this list.
*
* @param e the element to insert
* @return @code true (as specified by @link Deque#offerLast)
* @since 1.6
*/
public boolean offerLast(E e)
addLast(e);
return true;
/**
* Retrieves, but does not remove, the first element of this list,
* or returns @code null if this list is empty.
*
* @return the first element of this list, or @code null
* if this list is empty
* @since 1.6
*/
public E peekFirst()
final Node<E> f = first;
return (f == null) ? null : f.item;
/**
* Retrieves, but does not remove, the last element of this list,
* or returns @code null if this list is empty.
*
* @return the last element of this list, or @code null
* if this list is empty
* @since 1.6
*/
public E peekLast()
final Node<E> l = last;
return (l == null) ? null : l.item;
/**
* Retrieves and removes the first element of this list,
* or returns @code null if this list is empty.
*
* @return the first element of this list, or @code null if
* this list is empty
* @since 1.6
*/
public E pollFirst()
final Node<E> f = first;
return (f == null) ? null : unlinkFirst(f);
/**
* Retrieves and removes the last element of this list,
* or returns @code null if this list is empty.
*
* @return the last element of this list, or @code null if
* this list is empty
* @since 1.6
*/
public E pollLast()
final Node<E> l = last;
return (l == null) ? null : unlinkLast(l);
/**
* Pushes an element onto the stack represented by this list. In other
* words, inserts the element at the front of this list.
*
* <p>This method is equivalent to @link #addFirst.
*
* @param e the element to push
* @since 1.6
*/
public void push(E e)
addFirst(e);
/**
* Pops an element from the stack represented by this list. In other
* words, removes and returns the first element of this list.
*
* <p>This method is equivalent to @link #removeFirst().
*
* @return the element at the front of this list (which is the top
* of the stack represented by this list)
* @throws NoSuchElementException if this list is empty
* @since 1.6
*/
public E pop()
return removeFirst();
/**
* Removes the first occurrence of the specified element in this
* list (when traversing the list from head to tail). If the list
* does not contain the element, it is unchanged.
*
* @param o element to be removed from this list, if present
* @return @code true if the list contained the specified element
* @since 1.6
*/
public boolean removeFirstOccurrence(Object o)
return remove(o);
/**
* Removes the last occurrence of the specified element in this
* list (when traversing the list from head to tail). If the list
* does not contain the element, it is unchanged.
*
* @param o element to be removed from this list, if present
* @return @code true if the list contained the specified element
* @since 1.6
*/
public boolean removeLastOccurrence(Object o)
if (o == null)
for (Node<E> x = last; x != null; x = x.prev)
if (x.item == null)
unlink(x);
return true;
else
for (Node<E> x = last; x != null; x = x.prev)
if (o.equals(x.item))
unlink(x);
return true;
return false;
/**
* Returns a list-iterator of the elements in this list (in proper
* sequence), starting at the specified position in the list.
* Obeys the general contract of @code List.listIterator(int).<p>
*
* The list-iterator is <i>fail-fast</i>: if the list is structurally
* modified at any time after the Iterator is created, in any way except
* through the list-iterator's own @code remove or @code add
* methods, the list-iterator will throw a
* @code ConcurrentModificationException. Thus, in the face of
* concurrent modification, the iterator fails quickly and cleanly, rather
* than risking arbitrary, non-deterministic behavior at an undetermined
* time in the future.
*
* @param index index of the first element to be returned from the
* list-iterator (by a call to @code next)
* @return a ListIterator of the elements in this list (in proper
* sequence), starting at the specified position in the list
* @throws IndexOutOfBoundsException @inheritDoc
* @see List#listIterator(int)
*/
public ListIterator<E> listIterator(int index)
checkPositionIndex(index);
return new ListItr(index);
private class ListItr implements ListIterator<E>
private Node<E> lastReturned = null;
private Node<E> next;
private int nextIndex;
private int expectedModCount = modCount;
ListItr(int index)
// assert isPositionIndex(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();
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++;
public void forEachRemaining(Consumer<? super E> action)
Objects.requireNonNull(action);
while (modCount == expectedModCount && nextIndex < size)
action.accept(next.item);
lastReturned = next;
next = next.next;
nextIndex++;
checkForComodification();
final void checkForComodification()
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
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;
/**
* @since 1.6
*/
public Iterator<E> descendingIterator()
return new DescendingIterator();
/**
* Adapter to provide descending iterators via ListItr.previous
*/
private class DescendingIterator implements Iterator<E>
private final ListItr itr = new ListItr(size());
public boolean hasNext()
return itr.hasPrevious();
public E next()
return itr.previous();
public void remove()
itr.remove();
@SuppressWarnings("unchecked")
private LinkedList<E> superClone()
try
return (LinkedList<E>) super.clone();
catch (CloneNotSupportedException e)
throw new InternalError(e);
/**
* Returns a shallow copy of this @code LinkedList. (The elements
* themselves are not cloned.)
*
* @return a shallow copy of this @code LinkedList instance
*/
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;
/**
* Returns an array containing all of the elements in this list
* 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. (In other words, this method must allocate
* a new array). The caller is thus free to modify the returned array.
*
* <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()
Object[] result = new Object[size];
int i = 0;
for (Node<E> x = first; x != null; x = x.next)
result[i++] = x.item;
return result;
/**
* 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. 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.
*
* <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 list is set to @code 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.)
*
* <p>Like the @link #toArray() method, this method acts as bridge between
* array-based and collection-based APIs. Further, this method allows
* precise control over the runtime type of the output array, and may,
* under certain circumstances, be used to save allocation costs.
*
* <p>Suppose @code x is a list known to contain only strings.
* The following code can be used to dump the list into a newly
* allocated array of @code String:
*
* <pre>
* String[] y = x.toArray(new String[0]);</pre>
*
* Note that @code toArray(new Object[0]) is identical in function to
* @code toArray().
*
* @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)
a = (T[])java.lang.reflect.Array.newInstance(
a.getClass().getComponentType(), size);
int i = 0;
Object[] result = a;
for (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;
/**
* Saves the state of this @code LinkedList instance to a stream
* (that is, serializes it).
*
* @serialData The size of the list (the number of elements it
* contains) is emitted (int), followed by all of its
* elements (each an Object) in the proper order.
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException
// Write out any hidden serialization magic
s.defaultWriteObject();
// Write out size
s.writeInt(size);
// Write out all elements in the proper order.
for (Node<E> x = first; x != null; x = x.next)
s.writeObject(x.item);
/**
* Reconstitutes this @code LinkedList instance from a stream
* (that is, deserializes it).
*/
@SuppressWarnings("unchecked")
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException
// Read in any hidden serialization magic
s.defaultReadObject();
// Read in size
int size = s.readInt();
// Read in all elements in the proper order.
for (int i = 0; i < size; i++)
linkLast((E)s.readObject());
/**
* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
* and <em>fail-fast</em> @link Spliterator over the elements in this
* list.
*
* <p>The @code Spliterator reports @link Spliterator#SIZED and
* @link Spliterator#ORDERED. Overriding implementations should document
* the reporting of additional characteristic values.
*
* @implNote
* The @code Spliterator additionally reports @link Spliterator#SUBSIZED
* and implements @code trySplit to permit limited parallelism..
*
* @return a @code Spliterator over the elements in this list
* @since 1.8
*/
@Override
public Spliterator<E> spliterator()
return new LLSpliterator<E>(this, -1, 0);
/** A customized variant of Spliterators.IteratorSpliterator */
static final class LLSpliterator<E> implements Spliterator<E>
static final int BATCH_UNIT = 1 << 10; // batch array size increment
static final int MAX_BATCH = 1 << 25; // max batch array size;
final LinkedList<E> list; // null OK unless traversed
Node<E> current; // current node; null until initialized
int est; // size estimate; -1 until first needed
int expectedModCount; // initialized when est set
int batch; // batch size for splits
LLSpliterator(LinkedList<E> list, int est, int expectedModCount)
this.list = list;
this.est = est;
this.expectedModCount = expectedModCount;
final int getEst()
int s; // force initialization
final LinkedList<E> lst;
if ((s = est) < 0)
if ((lst = list) == null)
s = est = 0;
else
expectedModCount = lst.modCount;
current = lst.first;
s = est = lst.size;
return s;
public long estimateSize() return (long) getEst();
public Spliterator<E> trySplit()
Node<E> p;
int s = getEst();
if (s > 1 && (p = current) != null)
int n = batch + BATCH_UNIT;
if (n > s)
n = s;
if (n > MAX_BATCH)
n = MAX_BATCH;
Object[] a = new Object[n];
int j = 0;
do a[j++] = p.item; while ((p = p.next) != null && j < n);
current = p;
batch = j;
est = s - j;
return Spliterators.spliterator(a, 0, j, Spliterator.ORDERED);
return null;
public void forEachRemaining(Consumer<? super E> action)
Node<E> p; int n;
if (action == null) throw new NullPointerException();
if ((n = getEst()) > 0 && (p = current) != null)
current = null;
est = 0;
do
E e = p.item;
p = p.next;
action.accept(e);
while (p != null && --n > 0);
if (list.modCount != expectedModCount)
throw new ConcurrentModificationException();
public boolean tryAdvance(Consumer<? super E> action)
Node<E> p;
if (action == null) throw new NullPointerException();
if (getEst() > 0 && (p = current) != null)
--est;
E e = p.item;
current = p.next;
action.accept(e);
if (list.modCount != expectedModCount)
throw new ConcurrentModificationException();
return true;
return false;
public int characteristics()
return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
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