java util包学习（6） LinkedLIst 源码分析

重点就是LinkedList  先看看Deque双端对列接口

package java.util;

public interface Deque<E> extends Queue<E> {

void addFirst(E e);

void addLast(E e);

boolean offerFirst(E e);

boolean offerLast(E e);

E removeFirst();

E removeLast();

E pollFirst();

E pollLast();

E getFirst();

E getLast();

E peekFirst();

E peekLast();

boolean removeFirstOccurrence(Object o);//从此双端队列移除第一次出现的指定元素。

boolean removeLastOccurrence(Object o);

boolean add(E e);

boolean offer(E e);

E remove();

E poll();

E element();

E peek();

void push(E e);

E pop();

boolean remove(Object o);

boolean contains(Object o);

public int size();

Iterator<E> iterator();

Iterator<E> descendingIterator();

}

不难吧，，看看后面的实现类吧

package java.util;

public class LinkedList<E>
extends AbstractSequentialList<E>
implements List<E>, Deque<E>, Cloneable, java.io.Serializable
{
private transient Entry<E> header = new Entry<E>(null, null, null);//使用的是内部类  头结点  双向链表实现
private transient int size = 0;

public LinkedList() {
header.next = header.previous = header;//初始化
}

public LinkedList(Collection<? extends E> c) {
this();
addAll(c);
}

public E getFirst() {
if (size==0)
throw new NoSuchElementException();

return header.next.element;
}

public E getLast()  {
if (size==0)
throw new NoSuchElementException();

return header.previous.element;
}

public E removeFirst() {
return remove(header.next);
}

public E removeLast() {
return remove(header.previous);
}

public void addFirst(E e) {
addBefore(e, header.next);
}

public void addLast(E e) {
addBefore(e, header);
}

public boolean contains(Object o) {
return indexOf(o) != -1;
}

public int size() {
return size;
}

public boolean add(E e) {
addBefore(e, header);
return true;
}

public boolean remove(Object o) {
if (o==null) {
for (Entry<E> e = header.next; e != header; e = e.next) {
if (e.element==null) {
remove(e);
return true;
}
}
} else {
for (Entry<E> e = header.next; e != header; e = e.next) {
if (o.equals(e.element)) {
remove(e);
return true;
}
}
}
return false;
}

public boolean addAll(Collection<? extends E> c) {
return addAll(size, c);
}

public boolean addAll(int index, Collection<? extends E> c) {
if (index < 0 || index > size)
throw new IndexOutOfBoundsException("Index: "+index+
", Size: "+size);
Object[] a = c.toArray();
int numNew = a.length;
if (numNew==0)
return false;
modCount++;

Entry<E> successor = (index==size ? header : entry(index));
Entry<E> predecessor = successor.previous;
for (int i=0; i<numNew; i++) {
Entry<E> e = new Entry<E>((E)a[i], successor, predecessor);
predecessor.next = e;
predecessor = e;
}
successor.previous = predecessor;

size += numNew;
return true;
}

public void clear() {
Entry<E> e = header.next;
while (e != header) {
Entry<E> next = e.next;
e.next = e.previous = null;
e.element = null;
e = next;
}
header.next = header.previous = header;
size = 0;
modCount++;
}

public E get(int index) {
return entry(index).element;
}

public E set(int index, E element) {
Entry<E> e = entry(index);
E oldVal = e.element;
e.element = element;
return oldVal;
}

public void add(int index, E element) {
addBefore(element, (index==size ? header : entry(index)));
}

public E remove(int index) {
return remove(entry(index));
}

private Entry<E> entry(int index) {
if (index < 0 || index >= size)
throw new IndexOutOfBoundsException("Index: "+index+
", Size: "+size);
Entry<E> e = header;
if (index < (size >> 1)) {
for (int i = 0; i <= index; i++)
e = e.next;
} else {
for (int i = size; i > index; i--)
e = e.previous;
}
return e;
}

public int indexOf(Object o) {
int index = 0;
if (o==null) {
for (Entry e = header.next; e != header; e = e.next) {
if (e.element==null)
return index;
index++;
}
} else {
for (Entry e = header.next; e != header; e = e.next) {
if (o.equals(e.element))
return index;
index++;
}
}
return -1;
}

public int lastIndexOf(Object o) {
int index = size;
if (o==null) {
for (Entry e = header.previous; e != header; e = e.previous) {
index--;
if (e.element==null)
return index;
}
} else {
for (Entry e = header.previous; e != header; e = e.previous) {
index--;
if (o.equals(e.element))
return index;
}
}
return -1;
}

public E peek() {
if (size==0)
return null;
return getFirst();
}

public E element() {
return getFirst();
}

public E poll() {
if (size==0)
return null;
return removeFirst();
}

public E remove() {
return removeFirst();
}

public boolean offer(E e) {
return add(e);
}

public boolean offerFirst(E e) {
addFirst(e);
return true;
}

public boolean offerLast(E e) {
addLast(e);
return true;
}

public E peekFirst() {
if (size==0)
return null;
return getFirst();
}

public E peekLast() {
if (size==0)
return null;
return getLast();
}

public E pollFirst() {
if (size==0)
return null;
return removeFirst();
}

public E pollLast() {
if (size==0)
return null;
return removeLast();
}

public void push(E e) {
addFirst(e);
}

public E pop() {
return removeFirst();
}

public boolean removeFirstOccurrence(Object o) {
return remove(o);
}

public boolean removeLastOccurrence(Object o) {
if (o==null) {
for (Entry<E> e = header.previous; e != header; e = e.previous) {//从后往前
if (e.element==null) {
remove(e);
return true;
}
}
} else {
for (Entry<E> e = header.previous; e != header; e = e.previous) {
if (o.equals(e.element)) {
remove(e);
return true;
}
}
}
return false;
}

public ListIterator<E> listIterator(int index) {
return new ListItr(index);
}

private class ListItr implements ListIterator<E> {
private Entry<E> lastReturned = header;
private Entry<E> next;
private int nextIndex;
private int expectedModCount = modCount;

ListItr(int index) {
if (index < 0 || index > size)
throw new IndexOutOfBoundsException("Index: "+index+
", Size: "+size);
if (index < (size >> 1)) {
next = header.next;
for (nextIndex=0; nextIndex<index; nextIndex++)
next = next.next;
} else {
next = header;
for (nextIndex=size; nextIndex>index; nextIndex--)
next = next.previous;
}
}

public boolean hasNext() {
return nextIndex != size;
}

public E next() {
checkForComodification();
if (nextIndex == size)
throw new NoSuchElementException();

lastReturned = next;
next = next.next;
nextIndex++;
return lastReturned.element;
}

public boolean hasPrevious() {
return nextIndex != 0;
}

public E previous() {
if (nextIndex == 0)
throw new NoSuchElementException();

lastReturned = next = next.previous;
nextIndex--;
checkForComodification();
return lastReturned.element;
}

public int nextIndex() {
return nextIndex;
}

public int previousIndex() {
return nextIndex-1;
}

public void remove() {
checkForComodification();
Entry<E> lastNext = lastReturned.next;
try {
LinkedList.this.remove(lastReturned);
} catch (NoSuchElementException e) {
throw new IllegalStateException();
}
if (next==lastReturned)
next = lastNext;
else
nextIndex--;
lastReturned = header;
expectedModCount++;
}

public void set(E e) {
if (lastReturned == header)
throw new IllegalStateException();
checkForComodification();
lastReturned.element = e;
}

public void add(E e) {
checkForComodification();
lastReturned = header;
addBefore(e, next);
nextIndex++;
expectedModCount++;
}

final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}

private static class Entry<E> {
E element;//数据域
Entry<E> next;//双向链表
Entry<E> previous;

Entry(E element, Entry<E> next, Entry<E> previous) {
this.element = element;
this.next = next;
this.previous = previous;
}
}

private Entry<E> addBefore(E e, Entry<E> entry) {
Entry<E> newEntry = new Entry<E>(e, entry, entry.previous);
newEntry.previous.next = newEntry;//修改指针域改两面的
newEntry.next.previous = newEntry;
size++;
modCount++;
return newEntry;
}

private E remove(Entry<E> e) {
if (e == header)
throw new NoSuchElementException();

E result = e.element;
e.previous.next = e.next;
e.next.previous = e.previous;
e.next = e.previous = null;
e.element = null;//不需要e了 所以与它相关的指针域置为null
size--;
modCount++;
return result;
}

public Iterator<E> descendingIterator() {
return new DescendingIterator();
}

private class DescendingIterator implements Iterator {
final ListItr itr = new ListItr(size());
public boolean hasNext() {
return itr.hasPrevious();
}
public E next() {
return itr.previous();
}
public void remove() {
itr.remove();
}
}

public Object clone() {
LinkedList<E> clone = null;
try {
clone = (LinkedList<E>) super.clone();
} catch (CloneNotSupportedException e) {
throw new InternalError();
}

// Put clone into "virgin" state
clone.header = new Entry<E>(null, null, null);
clone.header.next = clone.header.previous = clone.header;
clone.size = 0;
clone.modCount = 0;

// Initialize clone with our elements
for (Entry<E> e = header.next; e != header; e = e.next)
clone.add(e.element);

return clone;
}

public Object[] toArray() {
Object[] result = new Object[size];
int i = 0;
for (Entry<E> e = header.next; e != header; e = e.next)
result[i++] = e.element;
return result;
}

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 (Entry<E> e = header.next; e != header; e = e.next)
result[i++] = e.element;

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 {
// Write out any hidden serialization magic
s.defaultWriteObject();

// Write out size
s.writeInt(size);

// Write out all elements in the proper order.
for (Entry e = header.next; e != header; e = e.next)
s.writeObject(e.element);
}

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();

// Initialize header
header = new Entry<E>(null, null, null);
header.next = header.previous = header;

// Read in all elements in the proper order.
for (int i=0; i<size; i++)
addBefore((E)s.readObject(), header);
}
}

LinkedList的实现使用的是双向循环链表，，静态内部类作为节点实现  最重要的其实是迭代器的实现  这也是设计模式的一个要点  虽然没有学习过，，还有一个很重要的问题，链表的迭代器是快速失败的，这是为何呢？我们知道其实，，很容易，快速失败的原因就是它继承了

AbstractList<E>类的modcount的字段，每修改集合时,就会发生变化，迭代器的快速失败原理就是要得到这个字段然后判断现在的modcount字段和开始初始化的modcount是否相等，相等才不会引发异常啊！！