泛型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实现一个链接列表。但是，当我运行setData()和setNext()方法时，会出现以下错误：

.\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，抛出错误似乎是因为有一种潜在的场景，即预先存在的this.data或this.next的类型与d或n不匹配。有什么方法可以用T#1 (新数据)覆盖T#1类型(先前的数据)吗？下面是带有构造函数和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;
  }

  //...

}

我很感激你能提供的任何帮助。提前感谢！

编辑:谢谢你的帮助！我已经删除了我的方法，但是当我从我的setNext类运行SinglyLinkedList ()时，仍然会得到以下错误：

.\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

因此，在我看来，getNext() (来自SinglyLinkedNode)和head (来自SinglyLinkedList)似乎没有返回任何值，尽管它们都应该返回SinglyLinkedNode对象。

这是有问题的代码。我已经标明了错误产生的地方。

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;
  }

  //...

如果还有人看到这篇文章，我会很感激他们能帮我做这件事。再次感谢！

编辑:我也修复了这个错误，它是

curr.setNext(toBeRemoved.getNext());

不

curr.setNext() = toBeRemoved.getNext()

Answer 1

你面临的问题其实很简单。基本上，您需要理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;
}

当您在方法的修饰符中放置一个<T>时，您正在使它成为一个通用方法。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，该方法将使用该对象作为其本地T值，这可能与全局类型T完全不同。

从方法修饰符中删除<T>将使它们成为常规的setter方法，并且默认为类类型T，它保证与所需的类型匹配。

Answer 2

您不需要在setter上使用泛型，因为它将处理与类处理的数据相同的数据。所以，你的代码会是这样的：

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

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

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

    //...

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

    //...

}

因此，现在可以创建SinglyLinkedNode实例并将值设置为：

public static void main(String[] args) {
    SinglyLinkedNode<Integer> integers = new SinglyLinkedNode<>(2);
    // 
}

另外，由于我已经有了一个设置值的构造函数，所以我会去掉setter。