类型参数不在类型变量的范围内 [英] type argument is not within bounds of type-variable

问题描述

嗨堆栈溢出社区^_^

基本上，我正在使用堆栈并将中缀方程转换为后缀方程.这是我尝试编译 Stack 类时在屏幕上显示的错误消息:

Basically, I am working with Stacks and converting from Infix to Postfix equations. This is the error message showing on screen when I am trying to compile the Stack class:

Stack.java:5: error: type argument T#1 is not within bounds of type-variable T#2
    private LinkedList<T> list;
                       ^
  where T#1,T#2 are type-variables:
    T#1 extends Object declared in class Stack
    T#2 extends Comparable<T#2> declared in class LinkedList

我在试图找出这个错误时遇到了真正的麻烦，但遗憾的是我不知道可能是什么问题.如果我知道得更好一点，我可以为您提供更多信息.

I am having real troubles trying to figure out this error but sadly I don't have a clue of what might be the problem. If I knew a little better I could have provided you with more info.

预先感谢您的任何评论和帮助！

Thanks in advance for any comments and help!

更新:这是我的课...

Update: Here is my class...

package ListPkg; 

public class Stack<T> //    implements Comparable<Stack>>  
{ 
    private LinkedList<T> list; 

    public Stack()
    {
        this("list");
    }
    public Stack(String name)
    {
        list = new LinkedList(name);
    }
    public void push(T item)
    {
        list.insertAtFront(item);
    }
    public T pop()
    {
        list.removeFromFront();
    }
    public int lenghtIs()
    {
        return list.lengthIs();
    }
    public T peek()
    {
        return list.returnFirstNode();
    }
    public void print()
    {
        list.print();
    }
    public boolean isEmpty()
    {
        return list.isEmpty();
    }
}

推荐答案

看来你有一个类 LinkedList 声明为

It seems you have a class LinkedList declared as

class LinkedList<T extends Comparable<T>> {...}

但是您试图在声明为

class Stack<T> {
    private LinkedList<T> list;
    ...
}

Stack中声明的类型变量T与LinkedList中的类型变量T完全无关.更重要的是，它们不兼容.LinkedList 期望一个类型是 Comparable 的子类型，但是 Stack 给它一个没有边界的类型参数.编译器不允许这样做.

The type variable T declared in Stack is completely unrelated to the type variable T in LinkedList. What's more, they are not compatible. LinkedList expects a type that is a sub type of Comparable, but Stack is giving it a type argument that has no bounds. The compiler cannot allow this.

为您的 Stack 类的类型参数添加适当的边界

Add appropriate bounds to your Stack class' type parameter

class Stack<T extends Comparable<T>> {

这篇关于类型参数不在类型变量的范围内的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！