Java HashMap作为字符串的ArrayList

首先，这是一个作业，所以我更多的是寻求帮助，然后是编码答案（不想作弊！）。我的任务是创建一个处理火车/火车站网络的程序。我所停留的部分添加电台及其连接，并将这些连接作为字符串数组列表返回。我已经在下面列出了到目前为止的代码，以及作业的摘录（与我现在所讲的部分相关）。我整个周末都在为这件事苦苦挣扎，所以任何帮助都将不胜感激

这只是我需要编辑的接口的实现，“MyNetwork”类。我只是觉得我一直在兜圈子，甚至可能还没有走上正轨

作业中的

public interface Network {

    /**
     * Add a station to the network.
     * @param station The station to be added.
     */
    public void addStation(String station);

    /**
     * Add a direct connection from one station to another.
     * @pre both fromStation and toStation have already been added by the method
     * addStation.
     * @param fromStation The station from which the connection begins. 
     * @param toStation The station at which the connection ends.
     */
    public void addConnection(String fromStation, String toStation);

    /**
     * Get a list of all stations directly connected to a given station.
     * @pre fromStation has been added to the network by the method addStation.
     * @param fromStation
     * @return A list of all the stations to which there is a direct connection
     * from fromStation. 
     */
    public String[] getConnections(String fromStation);

    /**
     * Search for a station in the network.
     * @param station Station to be searched for,
     * @return true if the Station exists in the network, false otherwise.
     */
    public boolean hasStation(String station);

    /**
     * Get all stations in the network.
     * @return An array containing all the stations in the network, with no
     * duplicates.
     */
    public String[] getStations();

创建一个实现网络接口的类MyNetwork

此类的getConnections方法应返回一个数组，该数组仅包含直接连接到fromStation参数的站。 提示1：您可以使用HashMap实现这一点，键是字符串（表示站点），值是字符串的ArrayList（表示直接连接到的站点）

提示2：尽管getConnections方法返回字符串数组，但是HashMap中的值最好是字符串数组列表

接口

public interface Network {

    /**
     * Add a station to the network.
     * @param station The station to be added.
     */
    public void addStation(String station);

    /**
     * Add a direct connection from one station to another.
     * @pre both fromStation and toStation have already been added by the method
     * addStation.
     * @param fromStation The station from which the connection begins. 
     * @param toStation The station at which the connection ends.
     */
    public void addConnection(String fromStation, String toStation);

    /**
     * Get a list of all stations directly connected to a given station.
     * @pre fromStation has been added to the network by the method addStation.
     * @param fromStation
     * @return A list of all the stations to which there is a direct connection
     * from fromStation. 
     */
    public String[] getConnections(String fromStation);

    /**
     * Search for a station in the network.
     * @param station Station to be searched for,
     * @return true if the Station exists in the network, false otherwise.
     */
    public boolean hasStation(String station);

    /**
     * Get all stations in the network.
     * @return An array containing all the stations in the network, with no
     * duplicates.
     */
    public String[] getStations();

实现：

public class MyNetwork implements Network {

    @Override
    public void addStation(String station) {

        ArrayList<String> Stations = new ArrayList<>();
        Stations.add(station);
    }

    @Override
    public void addConnection(String fromStation, String toStation) {

        Map<String,String> Connections = new HashMap<>();
        Connections.put(fromStation, toStation);
    }

    @Override
    public String[] getConnections(String fromStation) {
        return null; // dummy value!

    }

    @Override
    public boolean hasStation(String station) {
        return false; // dummy value!
    }

    @Override
    public String[] getStations() {
        return null; // dummy value!
    }
}

公共类MyNetwork实现网络{
@凌驾
公共站（字符串站）{
ArrayList Stations=新的ArrayList（）；
车站。添加（车站）；
}
@凌驾
public void addConnection（String fromStation、String toStation）{
Map Connections=newhashmap（）；
连接。放置（从站、到站）；
}
@凌驾
公共字符串[]getConnections（来自Station的字符串）{
返回null；//伪值！
}
@凌驾
公共布尔站（字符串站）{
返回false；//伪值！
}
@凌驾
公共字符串[]getStations（）{
返回null；//伪值！
}
}

您的网络需要有一个状态，使用一个或多个实例字段

就目前而言，它没有任何状态。每个方法都创建一个List或Map类型的局部变量，向该列表或Map添加一些内容，然后返回。因此，列表或映射直接超出范围并被垃圾收集

private Map<String, List<String>> stations = new HashMap<>();

// now all your methods should use the above map.

private Map stations=new HashMap（）；
//现在，所有方法都应该使用上面的映射。

---

请参见

为了清楚起见，将使用输入流将“电台”读入程序，但这是本作业的下一步。再次感谢！谢谢你，JB！我想我已经得到了你的建议，这肯定比我开始的更有意义。所以，对于“addConnections”方法，我应该参考地图“stations”，然后执行类似“put..From/to”的操作？不太可能。您必须获取已连接到站点的现有站点列表，并将给定的已连接站点添加到列表中。我更正了我的答案。地图应为

地图

，将连接的站点列表与站点相关联。