Question

在第110行，显示“ return front3”，我收到此错误。我不知道为什么，我在while循环中创建Node front3。

    public static Node add(Node poly1, Node poly2) {
        /** COMPLETE THIS METHOD **/
        // FOLLOWING LINE IS A PLACEHOLDER TO MAKE THIS METHOD COMPILE
        // CHANGE IT AS NEEDED FOR YOUR IMPLEMENTATION
        Node ptr1 = poly1;
        Node ptr2 = poly2;
        Node ptr3 = null;
        // Node front3;

        while (ptr1 != null && ptr2 != null) {
            if (ptr1.term.degree == ptr2.term.degree) {
                if (ptr3 == null) {
                    Node front3 = new Node(ptr1.term.coeff + ptr2.term.coeff,ptr1.term.degree,null);
                    ptr3 = front3;
                } else {
                    Node temp = new Node(ptr1.term.coeff + ptr2.term.coeff,ptr1.term.degree,null);
                    ptr3.next = temp;
                    ptr3 = temp;
                }
                ptr1 = ptr1.next;
                ptr2 = ptr2.next;
            } else if ( ptr1.term.degree > ptr2.term.degree) {
                if (ptr3 == null) {
                    Node front3 = new Node(ptr1.term.coeff,ptr1.term.degree,null);
                    ptr3 = front3;
                } else {
                    Node temp = new Node(ptr1.term.coeff, ptr1.term.degree , null);
                    ptr3.next = temp;
                    ptr3 = temp;
                }
                ptr1 = ptr1.next;
            } else if ( ptr1.term.degree < ptr2.term.degree ) {
                if (ptr3 == null) {
                    Node front3 = new Node(ptr2.term.coeff, ptr2.term.degree,null);
                    ptr3 = front3;
                } else {
                    Node temp = new Node(ptr2.term.coeff,ptr2.term.degree,null);
                    ptr3.next = temp;
                    ptr3 = temp;
                }
                ptr2 = ptr2.next;
            }
        }


        if (ptr3 == null) {
            return null;
        }

        return front3;
    }

然后我创建了另一个节点Node front4，将其初始化为某种东西，然后运行了程序。这是在while循环之外完成的。

Answer 1

发生这种情况是因为对象仅存在于声明的块内。对于您而言，您的front3仅存在于您用来声明它的if块中：

if (ptr3 == null) {
    Node front3 = new Node(ptr2.term.coeff, ptr2.term.degree,null);
    ptr3 = front3; // Can use it here
}
// Cannot use it here

如果确实需要返回front3对象，则应在“方法级别”中对其进行声明，这与对ptr节点的操作相同。实际上，您已经在此处发表了评论。如果您仅按以下方式应用更改，则应该可以进行：

当前：

// Node front3;

之后：

Node front3 = null; // Needs to initialize

您的if语句应更改为以下示例：

当前：

if (ptr3 == null) {
    Node front3 = new Node(ptr1.term.coeff,ptr1.term.degree,null);
    ptr3 = front3;
}

之后：

if (ptr3 == null) {
    front3 = new Node(ptr1.term.coeff,ptr1.term.degree,null); // No need for "Node", as it was already declared
    ptr3 = front3;
}

Ps。我没有审查逻辑。这只是为了解释为什么出现“变量名无法解析为变量” 错误。

变量名称无法解析为变量-我无法找到问题

1 个答案: