JAVA集合之LinkedList底层实现和原理

{"type":"doc","content":[{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"概述"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"LinkedList底层是基于双向链表"},{"type":"link","attrs":{"href":"https://blog.csdn.net/cb_lcl/article/details/81217972","title":""},"content":[{"type":"text","text":"(双向链表的特点)"}]},{"type":"text","text":"，链表在内存中不是连续的，而是通过引用来关联所有的元素，所以链表的优点在于添加和删除元素比较快，因为只是移动指针，并且不需要判断是否需要扩容，缺点是查询和遍历效率比较低。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":2,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"LinkedList是基于双向循环链表实现的，除了可以当做链表来操作外，实现了Deque接口，它还可以当做栈、队列和双端队列来使用。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":2,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"LinkedList同样是非线程安全的，只在单线程下适合使用。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":2,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"LinkedList实现了Serializable接口，因此它支持序列化，能够通过序列化传输，实现了Cloneable接口，能被克隆。"}]}]}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"数据结构"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"继承关系"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"java.lang.Object \n java.util.AbstractCollection \n java.util.AbstractList \n java.util.AbstractSequentialList \n java.util.LinkedList"}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"实现接口"}]},{"type":"codeblock","attrs":{"lang":"text"},"content":[{"type":"text","text":"Serializable, Cloneable, Iterable, Collection, Deque, List, Queue"}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"基本属性"}]},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"transient int size = 0; //LinkedList中存放的元素个数\ntransient Node first; //头节点\ntransient Node last; //尾节点"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"/**\n *LinkedList底层是双链表。\n *实现了List接口可以有队列操作\n *实现了Deque接口可以有双端队列操作\n *实现了所有可选的List操作并且允许存储任何元素，包括Null\n \n *所有的操作都提现了双链表的结构.\n *索引进入List的操作将从开始或者结尾遍历List，无论任何一个指定的索引\n *\n *注意：这些实现(linkedList)不是同步的，意味着线程不安全\n *如果有多个线程同时访问双链表，至少有一个线程在结构上修改list，那么就必须在外部加上同步操作(synchronized)(所谓的结构化修改\n *操作是指增加或者修改一个或者多个元素，重新设置元素的值不是结构化修改)，通常通过自然地同步一些对象来封装List来完成\n *\n *如果没有这样的对象存在，那么应该使用Collections.synchronizedList来封装链表。\n *最好是在创建是完成，以访问意外的对链表进行非同步的访问。\n *如：List list = Collections.synchronizedList(new LinkedList(...));\n *\n *此类的迭代器和迭代方法返回的迭代器是快速失败的：如果链表在迭代器被创建后的任何时间被结构化修改，除非是通过remove或者add方法操作的，\n *否则将会抛出ConcurrentModificationException异常，因此，面对高并发的修改，迭代器以后快速而干净的失败以防承担\n *冒着未确定的任意，非确定性行为的风险\n *\n *注意：迭代器快速失败的行为不能保证，一般来说，在存在并发修改的情况下不能确保任何的承诺，失败快速的迭代器\n *尽最大努力抛出ConcurrentModificationException异常，因此，编写一个依赖于此的程序是错误的。\n *正确性异常：迭代器的快速失败行为应该只用于检测错误\n *\n *\n *\n * @param \n */\npublic class LinkedList\nextends AbstractSequentialList\nimplements List, Deque, Cloneable, java.io.Serializable"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"重要方法解析"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"添加方法"}]},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"public boolean add(E e) {\n linkLast(e);\n return true;\n}\nvoid linkLast(E e) {\n final Node l = last;\n final Node newNode = new Node<>(l, e, null);\n last = newNode;\n if (l == null)\n first = newNode;\n else\n l.next = newNode;\n size++;\n modCount++;\n}"}]},{"type":"paragraph","attrs":{"indent":1,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"添加方法默认是添加到LinkedList的尾部，首先将last指定的节点赋值给l节点，然后新建节点newNode ,此节点的前驱指向l节点，data = e , next = null , 并将新节点赋值给last节点，它成为了最后一个节点，根据当前List是否为空做出相应的操作。若不为空将l的后继指针修改为newNodw。 size +1 , modCount＋１"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"删除方法"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"public boolean remove(Object o) {\n if (o == null) {\n for (Node x = first; x != null; x = x.next) {\n if (x.item == null) {\n unlink(x);\n return true;\n }\n }\n } else {\n for (Node x = first; x != null; x = x.next) {\n if (o.equals(x.item)) {\n unlink(x);\n return true;\n }\n }\n }\n return false;\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"删除方法，先循环遍历列表，找到item == o 的节点，在调用unlink()方法删除"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}