找不到符号变量…V扩展了在类中声明的对象

Question

我正在学校里学习Java，现在遇到了麻烦。

这是我的Graph.java文件：

package graph;

public interface Graph<V>{
    public boolean hasEdge(V one, V two);
    public void addNode(V other);
    public void addEdge(V other);
}

这是我的UndirectedGraph.java文件：

package graph.undirected;

import graph.*;
import java.util.*;

public class UndirectedGraph<V> implements Graph<V>{

    private HashMap<V,V> neighbourList;
    private TreeMap<V,V> prev;
    private TreeMap<V,Integer> dist;

    public UndirectedGraph(){
        neighbourList = new HashMap<V,V>();
        prev = new TreeMap<V,V>();
        dist = new TreeMap<V,Integer>();
    }

    public boolean hasEdge(V one, V two){
        if(!(this.neighbourList.containsKey(one) && this.neighbourList.containsKey(two))){
            throw new java.util.NoSuchElementException("Nonexistent node.");
        }
        else{
            if( one.neighbourList.containsKey(two) && two.neighbourList.containsKey(one) ){
                return false;
            }
            return true;
        }
    }
    public void addNode(V other){
        if(!(this.neighbourList.containsKey(other))){
            // some code will come here
        }
    }
    public void addEdge(V other){
        if(!(this.neighbourList.containsKey(other))){
            // and some code will come here too
        }
    }
}

我得到以下错误：

graph \\ undirected \\ UndirectedGraph.java：23：错误：找不到符号if（one.neighbourList.containsKey（two）&& two.neighbourList.containsKey（one））{^符号：variable neighbourList location：变量V类型之一，其中V是类型变量：V扩展了在类UndirectedGraph graph \\ undirected \\ UndirectedGraph.java：23中声明的对象：错误：找不到符号if（one.neighbourList.containsKey（two）&& two.neighbourList.containsKey（one））{^符号：变量neighbourList位置：类型V的变量2
其中V是类型变量：V扩展了在类UndirectedGraph中声明的对象2错误

我被困在这里。 谁能帮我？

Answer 1

one和two的类型为V ，在您的例子中，出于所有目的，它是一个Object 。 该类型V没有neighbourList字段，因此您无法在下面编写代码，因为它无法编译：

if( one.neighbourList.containsKey(two) && two.neighbourList.containsKey(one) ){