试图让这两种方法发挥作用，但我对泛型没有太多经验，而且这个概念让人很困惑。
anything getfirst（）：返回存储在列表中第一个节点中的值。它应该打印一条错误消息，如果列表为空，则返回null。
anything getlast（）：返回存储在列表中最后一个节点中的值。它应该打印一条错误消息，如果列表为空，则返回null。
这是我的代码：（上面的方法显示在底部）

public class Node<Anything>{

private Anything data;
private Node next;

Node(Anything a, Node n)
{
    data = a;
    next = n;
}

public Anything getData()
{ 
    return this.data;
}

public Anything setData(Anything newData)
{
    Anything oldData = this.data;
    this.data = newData;
    return oldData;
}

public void setNext(Node newNext)
{
    this.next = newNext;
}

public Node getNext()
{
    return this.next;
}
  }

-----------------------------------------------

public class CS2LinkedList<Anything>{  

private Node first;
private Node last;

public CS2LinkedList()
{
    first = null;
}

public boolean isEmpty()
{
    return (first == null);
}

public void addFirst(Anything d)
{
     Node temp = first;
     first = new Node(d,temp);
}

public void clear()
{
    first = null;
}

public boolean contains(Anything value)
{
    for (Node curr = first; curr != null; curr = curr.getNext())
    {
        if (value.equals(curr.getData())){
            return true;
        }
    }
    return false;
}

public String toString()
{
    StringBuilder result = new StringBuilder();  //String result = "";
    for (Node curr = first; curr != null; curr = curr.getNext())
        result.append(curr.getData() + "->");  //result = result + curr.data + "->";
    result.append("[null]");
    return result.toString();   //return result + "[null]";
}

public int size()
{   
    int size = 0;
    for (Node curr = first; curr != null; curr = curr.getNext()){
         size++;
         if (first==null){
                 size = 0;
            }
        }
        return size;
         }

// ------------------------ Question begins here ------------------------

public Anything getFirst()
{   
    if (first != null){
        // What should I return here? I tried returning first, (Anything) first, but none of them seems to work.
    }
    else{
        return null;
    }
}

public Anything getLast()
{
    if (first != null){
        // Same here
    }
    else{
        return null;
}
 }