LinkedList Matters needing attention

The LinkedList bottom is realized by bidirectional linked list, which can be used to realize stack, queue, bidirectional queue

1. Structure of each node
private Static Class Node {
E item;
Node Next;
Node prev;

    Node (node<e> prev, E element, node<e> next) {
        This.item = element;
        This.next = Next;
        This.prev = prev;
    }

-Note that we can add null to the LinkedList, when only the item equals NULL, and Next and Prev are still non-empty and do not affect the use

The 2.LinkedList class maintains the node of the both-A and the last, easy to operate
-first's prev is Null,last's next is null

3. With the one and last we can easily implement the stack, queue, two-way queue function
Add: public void AddFirst (e e);
public void AddLast (e e);
Delete: Public E removefirst ();
Public E removelast ();
Query: Public E peekfirst ();
Public E peeklast ();
4. Implement stack operation:
public void push (E e) {
AddFirst (e);
}
Public E pop () {
return Removefirst ();
}
Public E Peek () {
Final Node f = A;
return (f = null)? Null:f.item;
}
Note: size () will change after each pop, so you cannot traverse for (int i=0;i