继承关系
public class LinkedList<E>
extends AbstractSequentialList<E>
implements List<E>, Deque<E>, Cloneable, java.io.Serializable
public abstract class AbstractSequentialList<E> extends AbstractList<E>
public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E>
成员变量
1.集合的元素个数
transient int size = 0;
2.指向头的指针
transient Node<E> first;
3.指向尾的指针
transient Node<E> last;
4.node数据结构
//含指向前后节点的节点
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;
}
}
关键方法
1.构造方法
public LinkedList() {
}
public LinkedList(Collection<? extends E> c) {
this();
addAll(c);
}
2.添加元素
//在尾部添加元素
public boolean add(E e) {
linkLast(e);
return true;
}
//在指定位置添加元素
public void add(int index, E element) {
checkPositionIndex(index);
if (index == size)
linkLast(element);
else
linkBefore(element, node(index));
}
//在尾部添加集合
public boolean addAll(Collection<? extends E> c) {
return addAll(size, c);
}
//在指定位置添加集合
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;
}
//将该节点置为新链表的头部
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++;
}
//在链表的尾部增加一个节点
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++;
}
//在链表指定位置的前面增加一个节点
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++;
}
//根据下标，找到对应的节点
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;
}
}
继承自双端队列的添加方法
//入栈，其实就是在头部添加元素
public void push(E e) {
addFirst(e);
}
在尾部添加
public boolean offer(E e) {
return add(e);
}
//在头部添加
public boolean offerFirst(E e) {
addFirst(e);
return true;
}
//尾部添加
public boolean offerLast(E e) {
addLast(e);
return true;
}
分析
无论是添加一个元素还是一个集合，都得先确定要添加元素的位置
根据元素的位置，找到对应的节点
每个节点都有前后指针，改变指针的指向即可添加元素
3.删除元素
//删除头元素
public E remove() {
return removeFirst();
}
public E removeFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return unlinkFirst(f);
}
//删除指定元素
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;
}
//删除指定位置的元素
public E remove(int index) {
checkElementIndex(index);
return unlink(node(index));
}
//去除指定节点在链表中的关联
E unlink(Node<E> x) {
// assert x != null;
final E element = x.item;
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;
}
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;
}
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;
}
来自双端队列的移除操作
public E pop() {
return removeFirst();
}
public E poll() {
final Node<E> f = first;
return (f == null) ? null : unlinkFirst(f);
}
public E pollFirst() {
final Node<E> f = first;
return (f == null) ? null : unlinkFirst(f);
}
public E pollLast() {
final Node<E> l = last;
return (l == null) ? null : unlinkLast(l);
}
分析
无论是怎么样的删除操作，都是需要找到要删除的事哪个节点
找到节点后，将该节点的pre指向该节点的next即可，同时将本节点的值置为null
4.修改，查询元素
public E set(int index, E element) {
checkElementIndex(index);
Node<E> x = node(index);
E oldVal = x.item;
x.item = element;
return oldVal;
}
public E get(int index) {
checkElementIndex(index);
return node(index).item;
}
修改和查询操作都改变链表本来的结构
总结
LinkedList是一个链表结构的集合，这个链表的每一个节点都指向自己的前后节点，同时该链表有两个指针，一个指针指向链表的头部，一个指针指向链表的尾部
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