java - 使用LLList的代码中的错误

Question

我正在尝试编写代码，以从列表中删除所有一项，但是当我尝试使用表示空指针异常的方法时遇到错误。
哪一行导致此错误，我该如何解决？删除项目后，它还应该返回true；如果没有出现，则返回false。

更新:错误是该行对象item2 = trav.item

public boolean removeAll(Object item){
    Node trav = head;
    while(trav != null){
        Object item2 = trav.item;
        // it could be `item2.equals` 
        if(item2.equals(item)){
            trav.next = trav;
            return true;
        }
        trav = trav.next; 
    }  
    return false;
}

Answer 1

除了我修复您的NPE。

如果您在修复删除代码时遇到问题，请查看此作为引用，它已经过测试。

我加入评论以解释正在发生的事情。

public class LList {

    // very basic singly linked node
    class Node {
        public Node next;
        public Object item;
        public Node(Object o) {
            item = o;
        }
    }

    // the head and tail of this list
    Node head = null;
    Node tail = null;

    public boolean removeAll(Object item) {
        int count = 0;
        if (head == null)
            return false;

        // while `head.item.equals(item)` remove the head
        while (head != null && item.equals(head.item)) {
            head = head.next;
            count++;
        }
        // don't need to worry about updating `head` anymore
        // because now `!head.item.equals(item)`, else `head == null`
        if (head == null)
            return count > 0;

        // previous and current nodes
        Node prev = head; // !head.item.equals(item)
        Node curr = head.next;
        while (curr != null) {
            if (item.equals(curr.item)) {
                // to remove `curr` make the previous node skip it
                // and link to the next node instead
                prev.next = curr.next;
                count++;
            } else {
                // if curr was removed then prev stays put
                // otherwise curr is the new prev
                prev = curr;
            }
            // always move curr forward
            curr = curr.next;
        }
        return count > 0;
    }