在java中从双链接列表中删除第n个值

Question

oldVal（）方法这将得到删除节点所需的正确if、else if或else语句，但我总是得到一个空点异常。我将其与类似代码进行了比较，似乎无法找到它的错误

请帮助：

enter code here//    ***************************************************************
// DoubleLinked.java
//
// A class using a doubly linked list to represent a list of integers.
//
// ***************************************************************
public class DoubleLinked
{
private int size=0;
private IntNode list;
// ----------------------------------------------
// Constructor -- initializes list
// ----------------------------------------------
public DoubleLinked()
{
    list = null;
}
// ----------------------------------------------
// Prints the list elements
// ----------------------------------------------
public void print()
{
    for (IntNode temp = list; temp != null; temp = temp.next)
        System.out.println(temp.val);
}
// ----------------------------------------------
// Adds new element to front of list
// ----------------------------------------------
public void addToFront(int val)
{
    IntNode newNode = new IntNode(val);
    newNode.next = list;
    if (list != null)
        list.prev = newNode;
    list = newNode;
    size++;
}

public void addToEnd(int val)
{

    IntNode newNode = new IntNode(val);
    IntNode current;
    if (list == null)
        {list= newNode;}
    else
    {
        current=list;
        while(current.next != null)
            current = current.next;
        current.next = newNode;

    }
    size++;
}

public void removeFirst()
{
    IntNode test = list;

    if (test == null){System.out.println("your list is emty"); size++;}


    else if (list != null) { // list might be empty
        IntNode temp = list.prev;

            if(list.next==null && list.prev==null) {
                list=null;



            }
            else {
                list.next.prev = null;
                list = list.next;
            }
        }

size--;
    }


public void removeLast()
{
IntNode test = list;


    if (test == null){System.out.println("your list is emty");       size++;}

    else if(list.next==null && list.prev==null) 
    {
        list=null;
         }

    else if (list != null){
        IntNode current=list;
        while(current.next.next != null)
            current = current.next;
        current.next=null;
    }

size--;
}


    public void oldVal(int val)
    {
        IntNode temp=list;
          for (int i = 0; i < this.size; i++)
          {

              if (temp.val != val)
                temp= temp.next;
              else{

                   if  (temp.prev == null)
                    {    

                      list=list.next;
                    }
                  if (temp.next == null)
                    {    

                      temp.prev.next=null;
                    }
                  else
                  {

                     temp.prev.next=temp.next;
                     temp.next.prev=temp.prev;
                  }
                  size--;
                  break;
              }


        }}

//***************************************************************
// An inner class that represents a list element.
//***************************************************************
class IntNode
{
    public int val;
    public IntNode next;
    public IntNode prev;
    public IntNode(int val)
    {
        this.val = val;
        this.next = null;
        this.prev = null;
    }
}}