What is the time complexity of a size() call on a LinkedList in Java?

Question

正如标题所示，我想知道LinkedList类中的size（）方法是否需要分摊O（1）时间或O（n）时间。

Answer 1

It's O(1). You can google for the source code and you will come to such:

From http://www.docjar.com/html/api/java/util/LinkedList.java.html

All of the Collection classes I have looked at store a the size as a variable and don't iterate through everything to get it.

Answer 2

O(1) as you would have found had you looked at the source code...

From LinkedList:

private transient int size = 0;

...

/**
 * Returns the number of elements in this list.
 *
 * @return the number of elements in this list
 */
public int size() {
   return size;
}