java - Java 中的泛型在定义方法时抛出错误

Question

我正在学习 Java 中的泛型。为此，我尝试了一个简单的 LinkedList。

class Node {
  private int age;
  private String name;
  private Node next;

  public Node(int age, String name) {
    this.age = age;
    this.name = name;
    this.next = null;
  }

  public int getAge() {
    return this.age;
  }

  public String getName() {
    return this.name;
  }

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

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

class LinkedList<T> {
  private T head;
  private T current;

  public LinkedList() {
    head = null;
    current = null;
  }

  public void append(T x) {
    if (head == null) {
      head = x;
      current = x;
    }
    else {
      current.setNext(x);
      current = x;
    }
  }

  public T getAt(int index) {
    T ptr = head;
    for(int i = 0; i < index; i++) {
      ptr = ptr.getNext();
    }
    return ptr;
  }
}

class Main {
  public static void main(String[] args) {
    LinkedList<Node> list = new LinkedList<Node>();
    list.append(new Node(39, "John"));
    list.append(new Node(43, "Josh"));
    Node x = list.getAt(1);
    System.out.println(String.format("%d, %s", x.getAge(), x.getName()));
  }
}

但是我得到了这个错误，而所有的方法都存在于 Node 类中。我做错了什么？

LinkedList.java:16: error: cannot find symbol
      current.setNext(x);
             ^
  symbol:   method setNext(T)
  location: variable current of type T
  where T is a type-variable:
    T extends Object declared in class LinkedList
LinkedList.java:24: error: cannot find symbol
      ptr = ptr.getNext();
               ^
  symbol:   method getNext()
  location: variable ptr of type T
  where T is a type-variable:
    T extends Object declared in class LinkedList
2 errors

Answer 1

如果current类型为 T , 你不能调用 Node 的方法setNext() 上的类(例如 current ) , 自 T当你实例化你的 LinkedList 时可以被任何类替代.

你的 Node类不应该是 LinkedList 的泛型类型参数. LinkedList应始终由 Node 组成秒。每个 Node 中存储的数据类型应该是泛型。

class Node<T> {
  private T data;
  private Node next;

  public Node(T data) {
    this.data = data;
    this.next = null;
  }
}

还有 LinkedList应包含 Node<T>节点:

class LinkedList<T> {
  private Node<T> head;
  private Node<T> current;
}