找不到符號變量…V擴展了在類中聲明的對象

Question

我正在學校里學習Java，現在遇到了麻煩。

這是我的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);
}

這是我的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
        }
    }
}

我得到以下錯誤：

graph \\ undirected \\ UndirectedGraph.java：23：錯誤：找不到符號if（one.neighbourList.containsKey（two）&& two.neighbourList.containsKey（one））{^符號：variable neighbourList location：變量V類型之一，其中V是類型變量：V擴展了在類UndirectedGraph graph \\ undirected \\ UndirectedGraph.java：23中聲明的對象：錯誤：找不到符號if（one.neighbourList.containsKey（two）&& two.neighbourList.containsKey（one））{^符號：變量neighbourList位置：類型V的變量2
其中V是類型變量：V擴展了在類UndirectedGraph中聲明的對象2錯誤

我被困在這里。 誰能幫我？

Answer 1

one和two的類型為V ，在您的例子中，出於所有目的，它是一個Object 。 該類型V沒有neighbourList字段，因此您無法在下面編寫代碼，因為它無法編譯：

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