【Java8源码分析】集合框架-LinkedList
2017-05-02 16:22
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一、总结
(1)LinkedList有两个构造参数,一个为无參构造,只是新建一个空对象,第二个为有参构造,新建一个空对象,然后把所有元素添加进去。(2)LinkedList的存储单元为一个名为Node的内部类,包含pre指针,next指针,和item元素,实现为双向链表
(3)LinkedList的删除、添加操作时间复杂度为O(1),查找时间复杂度为O(n),查找函数有一定优化,容器会先判断查找的元素是离头部较近,还是尾部较近,来决定从头部开始遍历还是尾部开始遍历
(4)LinkedList实现了Deque接口,因此也可以作为栈、队列和双端队列来使用。
二、源码分析
package java.util; import java.util.function.Consumer; public class LinkedList<E> extends AbstractSequentialList<E> implements List<E>, Deque<E>, Cloneable, java.io.Serializable { transient int size = 0; // 记录了链表的第一个元素和第二个元素,为双向链表 transient Node<E> first; transient Node<E> last; public LinkedList() { } // 该构造函数,先创建一个空的LinkedList,然后把所有元素加进去 public LinkedList(Collection<? extends E> c) { this(); addAll(c); } // 把一个元素添加都第一个位置 // 注意:以下link、unlink开头的函数都为私有函数 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++; } // 把一个元素添加到最后一个位置 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++; } // 在某个元素前添加元素 void linkBefore(E e, Node<E> succ) { 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++; } // 删除第一个元素,注意传入的需为第一个元素,不然链表会出现违背本意情况 private E unlinkFirst(Node<E> f) { 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; } // 删除某个元素 private E unlinkLast(Node<E> l) { 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; } // 删除某个元素 E unlink(Node<E> x) { 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; } // 获取第一个元素 public E getFirst() { final Node<E> f = first; if (f == null) throw new NoSuchElementException(); return f.item; } // 获取最后一个元素 public E getLast() { final Node<E> l = last; if (l == null) throw new NoSuchElementException(); return l.item; } public E removeFirst() { final Node<E> f = first; if (f == null) throw new NoSuchElementException(); return unlinkFirst(f); } public E removeLast() { final Node<E> l = last; if (l == null) throw new NoSuchElementException(); return unlinkLast(l); } public void addFirst(E e) { linkFirst(e); } public void addLast(E e) { linkLast(e); } public boolean contains(Object o) { return indexOf(o) != -1; } public int size() { return size; } public boolean add(E e) { linkLast(e); return true; } // 只删除第一个出现的元素 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; } 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; } 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 = pr e8cc ed; } size += numNew; modCount++; return true; } public void clear() { // 确保GC能回收 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++; } // 以下为位置相关操作 public E get(int index) { checkElementIndex(index); return node(index).item; } 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)); } // 判断现有的链表范围,即 <= 0 < n private boolean isElementIndex(int index) { return index >= 0 && index < size; } // 判断是否为正确位置,如对于迭代器,或者添加操作,即 <= 0 <= n 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)); } // 该方法会判断元素离头部比较近,还是尾巴比较近,然后开始遍历 Node<E> node(int 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; } } 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; } // 以下为队列操作 public E peek() { final Node<E> f = first; return (f == null) ? null : f.item; } public E element() { return getFirst(); } public E poll() { final Node<E> f = first; return (f == null) ? null : unlinkFirst(f); } public E remove() { return removeFirst(); } public boolean offer(E e) { return add(e); } // 以下为双向队列操作 public boolean offerFirst(E e) { addFirst(e); return true; } public boolean offerLast(E e) { addLast(e); return true; } public E peekFirst() { final Node<E> f = first; return (f == null) ? null : f.item; } public E peekLast() { final Node<E> l = last; return (l == null) ? null : l.item; } 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); } 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 (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; } // 浅拷贝 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; } 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; } @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; // java.io.Serializable的写入函数 // 将LinkedList的“容量,所有的元素值”都写入到输出流中 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); } // java.io.Serializable的读取函数:根据写入方式反向读出 // 先将LinkedList的“容量”读出,然后将“所有的元素值”读出 @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()); } }
三、参考
http://blog.csdn.net/ns_code/article/details/35787253相关文章推荐
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