Question

我是泛型的新手，我正在尝试使用泛型SinglyLinkedNode实现链接列表。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，引发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？有什么办法可以用T＃2（新数据）覆盖T＃1（现有数据）的类型？这是带有构造函数和设置方法的类：

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。预先感谢！

编辑：谢谢您的帮助！我已经从方法中删除了，但是当我从SinglyLinkedList类中运行setNext（）时，仍然出现以下错误：

.\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，我觉得getNext（）（来自SinglyLinkedNode）和head（来自SinglyLinkedList）似乎没有返回任何值，即使它们都应该都返回SinglyLinkedNode对象。

这是有问题的代码。我已标记出错误发生的地方。

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;
  }

  //...

如果仍然有人看到这篇文章，如果能为我提供帮助，我将不胜感激。再次感谢！

编辑：我也修复了此错误；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;
}

当您将<T>放在方法的修饰符中时，即表示它是通用方法。泛型方法中的类型T不同，并且覆盖了整个类的类型T，这意味着您可以输入任何类型的对象，并且该方法会将其用作其局部T值，该值可能与全局值完全不同键入T。

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，这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class相同类型的数据。因此，您的代码将如下所示：

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，现在您可以创建SinglyLinkedNode实例，并将值设置为：

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

此外，由于已经有了用于设置值的构造函数，因此我将摆脱设置方法。

通用设置方法不兼容的类型错误

2 个答案: