链表的底层实现

此程序是头插法实现的链表且含有虚拟头节点

public class LinkedList<E> {
    private class Node<E>{
        E e;
        Node next;
        public Node (E e,Node next){
            this.e=e;
            this.next=next;
        }
        public Node(E e){
            this(e,null);
        }
        public Node(){
            this(null,null);
        }

        @Override
        public String toString() {
            return e.toString();
        }
    }
    private Node dummyHead;
    private int size;
    public  LinkedList(){
        dummyHead=new Node(null,null);
        size=0;
    }
    public int getSize(){
        return size;
    }
    public boolean isEmpty(){
        return size==0;
    }

    public void add(int index,E e){
        if(index<0 ||index>size)
            throw new IllegalArgumentException("Add Fail,Index error!");
        Node prev=dummyHead;
        for(int i=0; i<index; i++) {
            prev=prev.next;
        }
//      Node node =new Node(e);
//      node.next=prev.next;
//      prev.next=node;
        prev.next=new Node(e,prev.next);
        size++;
    }
    public void addLast(E e){
        add(size,e);
        size++;
    }
    public void addFirst(E e){
        add(0,e);
        size++;
    }
    public Node get(int index) {
        if(index<0 ||index>size)
            throw new IllegalArgumentException("Get Fail,Index error!");
        Node cur=dummyHead.next;
        for (int i=0; i<index;i++){
            cur=cur.next;
        }
        return cur;
    }
    public Node getFirst(){
        return get(0);
    }
    public Node getLast(){
        return get(size-1);
    }
    public void set(int index,E e){
        if(index<0 ||index>size)
            throw new IllegalArgumentException("Set Fail,Index error!");
        Node cur=dummyHead.next;
        for (int i=0; i<index;i++){
            cur.e=e;
        }
    }
    public boolean contains(E e) {
        Node cur=dummyHead.next;
        while(cur!=null) {
            if(cur.e.equals(e)){
                return true;
            }
            cur=cur.next;
        }
        return false;
    }
    public E remove(int index){
        if(index<0 ||index>size)
            throw new IllegalArgumentException("Get Fail,Index error!");
        Node prev=dummyHead;
        for(int i=0;i<index; i++){
            prev=prev.next;
        }
        Node retNode=prev.next;
        prev.next=retNode.next;
        retNode.next=null;
        size--;
        return (E) retNode.e;

    }
    @Override
    public String toString(){
        StringBuilder res = new StringBuilder();
        Node cur =dummyHead.next;
        while(cur != null){
        res.append(cur +"->");
            cur = cur. next ;
        }
        res.append( "NULL");
        return res.toString();
    }
    public static void main(String[] args){
        LinkedList<Integer> linkedList=new LinkedList<>();
        linkedList.addFirst(1);
        linkedList.addFirst(2);
        linkedList.addFirst(3);
        linkedList.addFirst(4);
        linkedList.addFirst(5);
        System.out.println(linkedList);
        linkedList.remove(2);
        System.out.println(linkedList);
    }
}

输出结果