Question

我在学校练习Java，现在我遇到了麻烦。

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
        }
    }
}

我收到了以下错误：

graph \ undirected \ UndirectedGraph.java:23:error：找不到符号                           if（one.neighbourList.containsKey（two）＆amp;＆amp; two.neighbourList.containsKey（one））{                                  ^符号：变量neighbourList location：V类型的变量，其中V是类型变量：       V扩展在类UndirectedGraph graph \ undirected \ UndirectedGraph.java中声明的Object：23：错误：找不到符号                           if（one.neighbourList.containsKey（two）＆amp;＆amp; two.neighbourList.containsKey（one））{                                                                        ^符号：变量neighbourList位置：变量二类型V
  其中V是一个类型变量：       V扩展在UndirectedGraph类错误中声明的Object

我被困在这里。任何人都可以帮助我吗？

Answer 1

one和two属于V类型，在您的示例中，所有用途都是Object。此类型V没有neighbourList字段，因此您无法在下面编写，因为它不会编译：

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

找不到符号变量... V extends在类中声明的Object

1 个答案: