LinkedList源码浅析(jdk1.8)
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LinkedList由双向链表实现的集合,因此可以从头或尾部双向循环遍历。
LinkedList的操作都是对双向链表的操作,理解双向链表的数据结构就很容易理解LinkedList的实现。
双向链表由带前驱和后继的节点构成,简易如下:
如果添加一个c节点,简易步骤如下:
先创建一个新节点。然后把原先的last节点的next指向新节点,在把新节点的pre指向原先的last,最后新节点指为last节点。
具体的双向链表还是参考数据结构的资料。
一、构造方法
1、无参的
public LinkedList() { }
2、集合为参数的
public LinkedList(Collection<? extends E> c) { this(); addAll(c); } public boolean addAll(Collection<? extends E> c) { return addAll(size, c); } public boolean addAll(int index, Collection<? extends E> c) { // 检查索引 checkPositionIndex(index); Object[] a = c.toArray(); int numNew = a.length; if (numNew == 0) return false; Node<E> pred, succ; // 索引为尾部还是范围内的 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; } private void checkPositionIndex(int index) { if (!isPositionIndex(index)) throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); } private boolean isPositionIndex(int index) { return index >= 0 && index <= size; }
二、添加元素
1、add(E e)方法,添加节点到尾部
public boolean add(E e) { linkLast(e); return true; } void linkLast(E e) { // 尾节点赋值给l final Node<E> l = last; // 构造新节点 final Node<E> newNode = new Node<>(l, e, null); // 新节点赋给尾节点 last = newNode; if (l == null) first = newNode; else l.next = newNode; size++; modCount++; }
2、addFirst(E e)方法,添加节点到首部
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++; }
三、删除元素
1、remove(Object o)方法,删除o节点(只删除一次),循环链表找到要删除的节点,然后调用unlink()方法进行删除。
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) { // 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; }
2、removeFirst()方法,删除首节点,为空则抛异常。
public E removeFirst() { final Node<E> f = first; if (f == null) throw new NoSuchElementException(); return unlinkFirst(f); } 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; }
四、其他方法源码
public class LinkedList<E> extends AbstractSequentialList<E> implements List<E>, Deque<E>, Cloneable, java.io.Serializable { transient int size = 0; /** * 首节点 */ transient Node<E> first; /** * 尾节点 */ transient Node<E> last; /** * 无参构造 */ public LinkedList() { } /** * 有参构造 */ public LinkedList(Collection<? extends E> c) { this(); addAll(c); } /** * 从头部添加元素(私有的,内部使用) */ 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++; } /** * 从尾部添加元素 */ 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++; } /** * 在指定元素前插入元素 */ 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++; } /** * 删除首节点(私有的,内部使用) */ 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; } /** * 删除尾节点(私有的,内部使用) */ 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; } /** * 删除节点x */ 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; } /** * 获取首节点 */ public E getFirst() { final Node<E> f = first; if (f == null) throw new NoSuchElementException(); return f.item; } /** * 获取尾节点 */ public E getLast() { final Node<E> l = last; if (l == null) throw new NoSuchElementException(); return l.item; } /** * 删除首节点并返回元素值 */ public E removeFirst() { final Node<E> f = first; if (f == null) throw new NoSuchElementException(); return unlinkFirst(f); } /** * 删除尾节点并返回元素值 */ public E removeLast() { final Node<E> l = last; if (l == null) throw new NoSuchElementException(); return unlinkLast(l); } /** * 把e设为首节点 */ public void addFirst(E e) { linkFirst(e); } /** * 把e设为尾节点 */ public void addLast(E e) { linkLast(e); } /** * 判断o是否在集合中 */ public boolean contains(Object o) { return indexOf(o) != -1; } /** * 集合大小 */ public int size() { return size; } /** * 添加元素到链表尾部 */ public boolean add(E e) { linkLast(e); return true; } /** * 删除o节点 */ 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 */ public boolean addAll(Collection<? extends E> c) { return addAll(size, c); } /** * 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; } /** * 清除集合所有元素 */ 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++; } // Positional Access Operations /** * 获取指定位置的元素的值 */ public E get(int index) { checkElementIndex(index); return node(index).item; } /** * 取代指定位置的元素并返回原元素的值 */ public E set(int index, E element) { checkElementIndex(index); Node<E> x = node(index); E oldVal = x.item; x.item = element; return oldVal; } /** * 添加元素到指定位置并后移原先的元素,如果指定的位置是最后,则直接添加元素在尾部 */ public void add(int index, E element) { checkPositionIndex(index); if (index == size) linkLast(element); else linkBefore(element, node(index)); } /** * 删除指定位置的元素 */ public E remove(int index) { checkElementIndex(index); return unlink(node(index)); } /** * 用于判断元素索引是否正确 */ private boolean isElementIndex(int index) { return index >= 0 && index < size; } /** * 用于判断位置索引是否正确 */ private boolean isPositionIndex(int index) { return index >= 0 && index <= size; } /** * 越界异常提示 */ 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)); } /** * 返回指定位置的节点. */ 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; } } // Search Operations /** * 从头循环返回第一次出现o的index */ 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; } /** * 从尾循环返回第一次出现o的index */ 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. /** * 返回首节点的值,但不删除,null也可以返回 */ public E peek() { final Node<E> f = first; return (f == null) ? null : f.item; } /** * 返回首节点的值,但不删除,如果是null则抛NoSuchElementException异常 */ public E element() { return getFirst(); } /** * 返回首节点并删除 */ public E poll() { final Node<E> f = first; return (f == null) ? null : unlinkFirst(f); } /** * 返回首节点并删除,如果首节点为null抛异常 */ public E remove() { return removeFirst(); } /** * 添加元素到尾节点 */ public boolean offer(E e) { return add(e); } // Deque operations /** * 添加元素到首节点前面 */ public boolean offerFirst(E e) { addFirst(e); return true; } /** * 添加元素到尾节点后面 */ public boolean offerLast(E e) { addLast(e); return true; } /** * 获取首节点不删除 */ public E peekFirst() { final Node<E> f = first; return (f == null) ? null : f.item; } /** * 获取尾节点不删除 */ public E peekLast() { final Node<E> l = last; return (l == null) ? null : l.item; } /** * 获取首节点并删除 */ public E pollFirst() { final Node<E> f = first; return (f == null) ? null : unlinkFirst(f); } /** * 获取尾节点并删除 */ public E pollLast() { final Node<E> l = last; return (l == null) ? null : unlinkLast(l); } /** * 添加元素到首节点前面 */ public void push(E e) { addFirst(e); } /** * 移除并返回首节点 */ public E pop() { return removeFirst(); } // 节点构造 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; } } /** * 集合转成数组 */ 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; } }
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