java - 退货

我试图返回一个集合，该集合包含在特定站点开始或结束的网络中的连接。我在弄清楚如何返回它并采用station参数时遇到了麻烦。还有在方法中创建hashMap的正确方法，还是应该在该方法之外创建它？

它给我return语句的错误incompatible types: Connection cannot be converted to Collection<Connection>

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);
}

最佳答案

仅返回一个Connection。您可以将退货类型更改为：

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

在您的情况下，映射为空，它将始终返回null。

关于java - 退货，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/36607594/