这个错误如题很奇怪,dubug下提示类中的Node类空指针,而直接运行就不会报错误,图如下

正常执行

dubug运行

内部实现代码如下

package utils;

/**

 * @author yqs

 * @description

 * @time 2019/7/13 18:09

 */

public class SingleLinked<E> {

    private int size;

    private Node<E> dummyHead;

    public SingleLinked(){

        dummyHead = new Node<>();

    }

    private class Node<E>{

        private Node next;

        private E element;

        public Node(){

            this(null, null);

        }

        public Node(E element,Node next){

            this.element = element;

            this.next = next;

        }

        @Override

        public String toString(){

            if (element!=null){

                return element.toString();

            }

            return null;

        }

    }

    public void addFirst(E e) {

        dummyHead.next = new Node<>(e,dummyHead.next);

        size++;

    }

    //指定位置添加元素

    public void add(E e, int index) {

        if (index < 0 || index > size) {

            throw new IllegalArgumentException("index is illegal,add failed");

        }

        Node head = dummyHead;

        for (int i = 0; i < index; i++) {

            head = head.next;

        }

        head.next = new Node(e,head.next);

        size++;

    }

    public void addLast(E e){

        add(e,size);

    }

    //在指定位置删除元素

    public E remove(int index){

        //System.out.println(dummyHead);

        //存虚拟头结点

        Node<E> prev = dummyHead;

        for (int i = 0; i < index; i++) {

            prev = prev.next;

        }

        //将当前元素存入prev_temp临时变量中

        Node<E> prev_temp = prev.next;

        //将当前元素的前一个节点的next指向当前元素的下一个节点;

        prev.next = prev_temp.next;

        //将当前元素的next设置为null等待虚拟机回收

        prev_temp.next = null;

        size--;

        return prev_temp.element;

    }

    public int getSize() {

        return size;

    }

    public boolean isEmpty(){

        return size == 0;

    }

    @Override

    public String toString(){

        StringBuilder sb = new StringBuilder();

        for (int i = 0; i < size; i++) {

            sb.append(dummyHead.next);

            sb.append(",");

            dummyHead = dummyHead.next;

        }

        return sb.toString();

    }

}

另外,要是换成双向链表要加一个尾节点,还有要不要在Node类中加一个prev节点指向上一个呢,我看网上有的教程并没有加这个prev,jdk源码加了