链表变量初始化遇到麻烦

Question

I'm having trouble with my Delete(Node p) method, I almost have it completely done but whenever I try to compile it, it says that previous may not have been previously initialized. Specifically in then if statement in this method below. I'm brand new to linked lists so I was just trying to practice getting the syntax right. Any help would be awesome. Thanks Guys.

public Node delete(Node p)
    {
        Node current, previous;
        current = head.next;

        while (current.info != p.info && current.next != null)
        {
            previous = current;
            current = current.next;
        }

        if (current.info == p.info)
        {
            previous.next = current.next;
            //this previous here is what is giving me trouble
        }
        return current;
    }

//end of trouble method, start of whole code

public class LinkedList
    {
        Node head;

        public class Node
        {
            int info;
            Node next;
            Node(int d)
            {
                info = d;
                next = null;
            }
        }

        public void insertAfter(Node prevnode, int new_info)
        {
            if (prevnode == null)
            {
                System.out.println("The given previous node cannot be null");
                return;
            }
            Node newnode = new Node(new_info);
            newnode.next = prevnode.next;
            prevnode.next = newnode;
        }

        public void insertEnd(int new_info)
        {
            Node newnode = new Node(new_info);
            if (head == null)
            {
                head = new Node(new_info);
                return;
            }
            newnode.next = null;
            Node last = head;
            while(last.next != null)
            {
                last = last.next;
            }
            last.next = newnode;
            return;
        }

        public void insertFirst(int new_info)
        {
            Node newnode = new Node(new_info);
            newnode.next = head;
            head = newnode;
        }

        public Node delete(Node p)
        {
            Node current, previous;
            current = head.next;

            while (current.info != p.info && current.next != null)
            {
                previous = current;
                current = current.next;
            }

            if (current.info == p.info)
            {
                previous.next = current.next;
            }
            return current;
        }

        public void printList()
        {
            Node tnode = head;
            while (tnode != null)
            {
                System.out.print(tnode.info + " ");
                tnode = tnode.next;
            }
        }

        public static void main(String[] args)
        {
            LinkedList slist = new LinkedList();
            slist.insertEnd(6);
            slist.insertFirst(7);
            slist.insertFirst(1);
            slist.insertEnd(4);
            slist.insertAfter(slist.head.next, 8);

            System.out.println("Top Ten Gaming Scores Are: ");
            slist.printList();

        }
    }

Answer 1

If the condition in your while loop: while (current.info != p.info && current.next != null) never evaluates to true, you do not enter the loop and as the warning says previous may not be initialized when you go to use it.

You should make sure to check that previous != null before you use it in the if statement.

Answer 2

You have to always initialize local variables . Setting previous =null before the while block will resolve your issues.

public Node delete(Node p)
    {
        Node current; 
        Node previous =null;
        current = head.next;

        while (current.info != p.info && current.next != null)
        {
            previous = current;
            current = current.next;
        }

        if (current.info == p.info)
        {
            previous.next = current.next;
            //this previous here is what is giving me trouble
        }
        return current;
    }