19java原始碼解析-LinkedList（一）
阿新 • • 發佈：2018-11-23
其他 原始碼解析 https://blog.csdn.net/qq_32726809/article/category/8035214
通過大體瀏覽原始碼，可知，Linkedlist的儲存機構是一個連結串列
類的宣告
public class LinkedList<E>
extends AbstractSequentialList<E>
implements List<E>, Deque<E>, Cloneable, java.io.Serializable
- AbstractSequentialList
- 順序集合介面的最小實現
- 若是隨機插入，則優先用AbstractList
- Deque
- 刪除和插入的集合，雙端對列
節點內部類
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; } }
next 指的是下一個節點，prev指的是上一個節點，item指的是當前節點的元素。可以將next和perv理解為指標。
屬性
transient int size = 0;
transient Node<E> first;/*第一個節點*/
transient Node<E> last;/*最後一個節點*/
建構函式
public LinkedList(Collection<? extends E> c) {
this();
addAll(c);
}
按照集合的迭代器的元素獲取建構函式
3方法
3.1linkFirst
把元素e作為第一個元素
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++;
}
將node節點上一個元素置為null，下一個元素為 原第一個元素，並將現在的元素賦予 first
3.2linkLast
把元素e多為最後一個元素
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++;
}
將當前元素新建一個node節點，把尾部的節點作為這個節點的上一個節點，把下一個節點置為null，把這個節點作為上一個節點的下一個節點，總的來說，就是把新節點與原來的節點連線起來.
3.3linkBefore
把元素e插入到 succ元素之前
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++;
}
類似於在兩個火車車廂中間插入新的車廂，需要舊的車廂與新的車廂頭尾相連，並改變車廂數
3.4unlinkFirst
將第一個元素移除連結
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;
}
3.5unlinkLast
將最後一個元素移除處連結
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;
}
3.6getFirst
獲取第一個元素
public E getFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return f.item;
}
3.7getLast
獲取最後一個元素
public E getLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return l.item;
}
3.8removeFirst(),removeLast(),addFirst(E e),addLast(E e)
這些方法用的是上面已經講過的方法
public E removeFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return unlinkFirst(f);
}
/**
* Removes and returns the last element from this list.
*
* @return the last element from this list
* @throws NoSuchElementException if this list is empty
*/
public E removeLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return unlinkLast(l);
}
/**
* Inserts the specified element at the beginning of this list.
*
* @param e the element to add
*/
public void addFirst(E e) {
linkFirst(e);
}
/**
* Appends the specified element to the end of this list.
*
* <p>This method is equivalent to {@link #add}.
*
* @param e the element to add
*/
public void addLast(E e) {
linkLast(e);
}
3.9contains
判斷元素是否在集合中，其實就是判斷節點的索引是否大於小於0
public boolean contains(Object o) {
return indexOf(o) != -1;
}
public int indexOf(Object o) {/*--------------1*/
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) {/*--------------2*/
if (o.equals(x.item))
return index;
index++;
}
}
return -1;
}
- 1處方法的是獲取元素的所在位置
- 2處是遍歷鏈條，對每個節點進行判斷。
3.10add
public boolean add(E e) {
linkLast(e);
return true;
}
新新增的元素會被新增到最後
3.11 remove
通過遍歷連結串列移除元素
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;
}
E unlink(Node<E> x) { /*-------------1*/
// 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;
}
1處的函式是刪除元素，然後將刪除後的兩端重新連結起來
3.12addAll
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;
}
/*-----------------------1*/
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;
}
1處為核心程式碼，就是把集合轉化的陣列進行遍歷，然後將元素新建成節點，再將節點連結起來
3.13clear
將所有連線元素設定為空
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++;
}