java - 为什么在对 LinkedList 使用 add() 和 getFirst() 时出现此错误？

Question

这是我的代码:

public class FlightMap implements FlightMapInterface {

LinkedList<City> cityList = new LinkedList<City>();
LinkedList<City> nextCity = new LinkedList<City>();

/**
 * Creates an empty FlightMap
 */
public FlightMap() {        
}


public void loadFlightMap(String cityFileName, String flightFileName)
        throws FileNotFoundException {

    File cityList = new File(cityFileName);
    File flightsTo = new File (flightFileName);

    Scanner theCityFile = null;
    Scanner theFlightFile = null;
    Scanner theRequestFile = null;

    ArrayList<String> cityStringList = new ArrayList<String>();
    int counter = 0;

    try {
        theCityFile = new Scanner (cityList);
        theFlightFile = new Scanner (flightsTo);
    }
    catch (FileNotFoundException e) {
        System.out.println("No such file exists.");
    }

    while (theFlightFile.hasNextLine()) {
        cityStringList.add((theFlightFile.nextLine()).replaceAll("\t", ""));
    }

    while (theCityFile.hasNextLine()) {
        LinkedList<City> tempList = new LinkedList<City>();
        String tempCity = theCityFile.nextLine();
        nextCity.add(tempList); // ERROR
        nextCity.get(counter).add(new City(tempCity)); // ERROR

        for (int x = 0; x < cityStringList.size(); x++) {
            if (cityStringList.get(x).charAt(0) == tempCity.charAt(0)) {
                insertAdjacent(nextCity.get(counter).getFirst(), // ERROR
                        new City(cityStringList.get(x)).charAt(1) + "");  // ERROR
            }
        }
        cityList.add(new City(tempCity)); // ERROR
        counter++;
    }
}

对于我的错误:

• 线程“main”java.lang.Error中出现异常: Unresolved 编译问题:
• LinkedList 类型中的 add(City) 方法不适用于参数 (LinkedList)
• 未针对 City 类型定义 add(City) 方法
• 未定义 City 类型的 getFirst() 方法
• 未针对 City 类型定义 charAt(int) 方法

Answer 1

正是错误所说的内容。

LinkedList<City> tempList = new LinkedList<City>();
String tempCity = theCityFile.nextLine();
nextCity.add(tempList);

应该是

String tempCity = theCityFile.nextLine();
nextCity.add(tempCity);

您尝试将一个 LinkedList 添加到另一个 LinkedList。您只能将 City 类型的“节点”添加到您声明的 LinkedList 中。