java - 通用 setter 方法不兼容类型错误

Question

我是泛型的新手，我正在尝试使用泛型类 SinglyLinkedNode 来实现链表。但是，当我运行 setData() 和 setNext() 方法时，出现以下错误:

.\singlyLinkedList\SinglyLinkedNode.java:13: error: incompatible types: T#1 cannot be 
converted to T#2
this.data = d;
            ^
where T#1,T#2 are type-variables:
  T#1 extends Object declared in method <T#1>setData(T#1)
  T#2 extends Object declared in class SinglyLinkedNode
.\singlyLinkedList\SinglyLinkedNode.java:21: error: incompatible types: 
SinglyLinkedNode<T#1> cannot be converted to SinglyLinkedNode<T#2>
this.next = n;
            ^
where T#1,T#2 are type-variables:
  T#1 extends Object declared in method <T#1>setNext(SinglyLinkedNode<T#1>)
  T#2 extends Object declared in class SinglyLinkedNode

在我看来，抛出该错误是因为存在潜在的情况，其中预先存在的 this.data 或 this.next 的类型与 d 或 n 不匹配。我该如何解决这个问题？有什么方法可以用 T#2 (新数据)覆盖 T#1 (预先存在的数据)的类型吗？这是带有我的构造函数和 setter 方法的类:

public class SinglyLinkedNode<T> {
  private T data;
  private SinglyLinkedNode<T> next;

  SinglyLinkedNode(T d) {
    this.data = d;
    this.next = null;
  }

  public <T> void setData(T d) {
    this.data = d;
  }

  //...

  public <T> void setNext(SinglyLinkedNode<T> n) {
    this.next = n;
  }

  //...

}

感谢您提供的任何帮助。提前致谢!

编辑:感谢您的帮助!我已从方法中删除，但当我从 SinglyLinkedList 类运行 setNext() 时，仍然收到以下错误:

.\singlyLinkedList\SinglyLinkedList.java:63: error: method setNext in class SinglyLinkedNode<T#2> cannot be applied to given types;
    curr.setNext() = toBeRemoved.getNext();
        ^
  required: SinglyLinkedNode<T#1>
  found: no arguments
  reason: actual and formal argument lists differ in length
  where T#1,T#2 are type-variables:
    T#1 extends Object declared in class SinglyLinkedList
    T#2 extends Object declared in class SinglyLinkedNode
.\singlyLinkedList\SinglyLinkedList.java:79: error: method setNext in class SinglyLinkedNode<T#2> cannot be applied to given types;
    prev.setNext() = this.head;
        ^
  required: SinglyLinkedNode<T#1>
  found: no arguments
  reason: actual and formal argument lists differ in length
  where T#1,T#2 are type-variables:
    T#1 extends Object declared in class SinglyLinkedList
    T#2 extends Object declared in class SinglyLinkedNode
.\singlyLinkedList\SinglyLinkedList.java:82: error: method setNext in class SinglyLinkedNode<T#2> cannot be applied to given types;
        prev.setNext() = curr.getNext();
            ^
  required: SinglyLinkedNode<T#1>
  found: no arguments
  reason: actual and formal argument lists differ in length
  where T#1,T#2 are type-variables:
    T#1 extends Object declared in class SinglyLinkedList
    T#2 extends Object declared in class SinglyLinkedNode

所以在我看来， getNext() (来自 SinglyLinkedNode)和 head (来自 SinglyLinkedList)没有返回任何值，即使它们都应该返回 SinglyLinkedNode 对象。

这是有问题的代码。我已经标记了出现错误的位置。

public class SinglyLinkedList<T> {
  private int size;
  private SinglyLinkedNode<T> head;
  private SinglyLinkedNode<T> tail;

  SinglyLinkedList() {
    this.size = 0;
    this.head = null;
    this.tail = null;
  }

  //...

  public SinglyLinkedNode<T> remove(int i) {
    SinglyLinkedNode<T> curr = this.head;
    for(int counter = 0; counter < i; counter++) {
      curr = curr.getNext();               //<---------------
    }
    SinglyLinkedNode<T> toBeRemoved = curr.getNext();
    curr.setNext() = toBeRemoved.getNext();
    this.size--;
    return toBeRemoved;
  }

  //...

  public SinglyLinkedNode<T> remove(T d) {
    if(this.head == null) {
      return null;
    }
    if(this.head.getData() == d) {
      SinglyLinkedNode<T> toBeRemoved = this.head;
      this.head = this.head.getNext();
      return toBeRemoved;
    }
    SinglyLinkedNode<T> curr = this.head;
    SinglyLinkedNode<T> prev = null;
    prev.setNext() = this.head;           //<---------------
    while(curr.getNext() != null) {
      if(curr.getData() == d) {
        prev.setNext() = curr.getNext();  //<---------------
        return curr;
      }
    }
    return null;
  }

  //...

如果有人仍然看到这篇文章，如果他们能帮助我，我将不胜感激。再次感谢!

编辑:我也修复了这个错误；这是

curr.setNext(toBeRemoved.getNext());

不是

curr.setNext() = toBeRemoved.getNext()

Answer 1

您面临的问题实际上非常简单。基本上，您需要了解泛型方法完全独立于泛型类。

public <T> void setData(T d) {
this.data = d;
}

public <T> void setNext(SinglyLinkedNode<T> n) {
    this.next = n;
}

当你输入 <T>在方法的修饰符中，您将其设为通用方法。泛型方法中的类型 T 是不同的，并且覆盖整个类的类型 T，这意味着您可以输入任何类型的对象，该方法将使用它作为其本地 T 值，这可以与全局 T 值完全不同输入 T。

删除<T>从你的方法修饰符将使它们成为常规的 setter 方法，并默认为类类型 T，保证与所需的类型匹配。