java - 归还藏品

Question

我正在尝试返回一个集合，其中包含在特定站点开始或结束的网络中的连接。我无法弄清楚如何返回它并获取站参数。在方法中创建 hashMap 是否也是正确的方法，还是应该在它之外创建？

它给我错误 incompatible types: Connection cannot be converted to Collection<Connection>对于返回语句

代码:

/**
 * Return a Collection containing all the Connections in the network that
 * start or end at a specified station
 *
 * @param station Station to/from which the Connection should run
 *
 * @return a Collection containing all the connections that start or end at
 * the specified station
 */

@Override
public Collection<Connection> getConnectionsFrom(Station station) {
    Map<Station, Connection> stationConnectionFrom = new HashMap<Station, Connection>();
    return stationConnectionFrom.get(station);
}

Answer 1

只返回一个Connection。您可以将返回类型更改为:

public Connection getConnectionFrom(Station station) {
    Map<Station, Connection> stationConnectionFrom = new HashMap<>();
    return stationConnectionFrom.get(station);
}

在您的情况下， map 为空，这将始终返回 null。