LinkedList (linked list) of java collection-unfinished

Reference blog:

1. Detailed explanation of LinkedList of java collection: https://blog.csdn.net/zhao_xinhu/article/details/82713574
2. What is a linear table (super detailed): https://blog.csdn.net/qq_25775935/article/details/88539848
3. Linked list of data structures-moving picture demo: https://www.cnblogs.com/newobjectcc/p/11798410.html

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