JAVA集合之LinkedList底層實現和原理

{"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底層是基於雙向鏈表"},{"type":"link","attrs":{"href":"https://blog.csdn.net/cb_lcl/article/details/81217972","title":""},"content":[{"type":"text","text":"(雙向鏈表的特點)"}]},{"type":"text","text":"，鏈表在內存中不是連續的，而是通過引用來關聯所有的元素，所以鏈表的優點在於添加和刪除元素比較快，因爲只是移動指針，並且不需要判斷是否需要擴容，缺點是查詢和遍歷效率比較低。"}]},{"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是基於雙向循環鏈表實現的，除了可以當做鏈表來操作外，實現了Deque接口，它還可以當做棧、隊列和雙端隊列來使用。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":2,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"LinkedList同樣是非線程安全的，只在單線程下適合使用。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":2,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"LinkedList實現了Serializable接口，因此它支持序列化，能夠通過序列化傳輸，實現了Cloneable接口，能被克隆。"}]}]}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"數據結構"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"繼承關係"}]},{"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":"實現接口"}]},{"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":"基本屬性"}]},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"transient int size = 0; //LinkedList中存放的元素個數\ntransient Node first; //頭節點\ntransient Node last; //尾節點"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"/**\n *LinkedList底層是雙鏈表。\n *實現了List接口可以有隊列操作\n *實現了Deque接口可以有雙端隊列操作\n *實現了所有可選的List操作並且允許存儲任何元素，包括Null\n \n *所有的操作都提現了雙鏈表的結構.\n *索引進入List的操作將從開始或者結尾遍歷List，無論任何一個指定的索引\n *\n *注意：這些實現(linkedList)不是同步的，意味着線程不安全\n *如果有多個線程同時訪問雙鏈表，至少有一個線程在結構上修改list，那麼就必須在外部加上同步操作(synchronized)(所謂的結構化修改\n *操作是指增加或者修改一個或者多個元素，重新設置元素的值不是結構化修改)，通常通過自然地同步一些對象來封裝List來完成\n *\n *如果沒有這樣的對象存在，那麼應該使用Collections.synchronizedList來封裝鏈表。\n *最好是在創建是完成，以訪問意外的對鏈表進行非同步的訪問。\n *如：List list = Collections.synchronizedList(new LinkedList(...));\n *\n *此類的迭代器和迭代方法返回的迭代器是快速失敗的：如果鏈表在迭代器被創建後的任何時間被結構化修改，除非是通過remove或者add方法操作的，\n *否則將會拋出ConcurrentModificationException異常，因此，面對高併發的修改，迭代器以後快速而乾淨的失敗以防承擔\n *冒着未確定的任意，非確定性行爲的風險\n *\n *注意：迭代器快速失敗的行爲不能保證，一般來說，在存在併發修改的情況下不能確保任何的承諾，失敗快速的迭代器\n *盡最大努力拋出ConcurrentModificationException異常，因此，編寫一個依賴於此的程序是錯誤的。\n *正確性異常：迭代器的快速失敗行爲應該只用於檢測錯誤\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":"添加方法默認是添加到LinkedList的尾部，首先將last指定的節點賦值給l節點，然後新建節點newNode ,此節點的前驅指向l節點，data = e , next = null , 並將新節點賦值給last節點，它成爲了最後一個節點，根據當前List是否爲空做出相應的操作。若不爲空將l的後繼指針修改爲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":"刪除方法"}]},{"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":"刪除方法，先循環遍歷列表，找到item == o 的節點，在調用unlink()方法刪除"}]},{"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}}]}