Question

我正在用Java做一个基本的GPS流程项目。它的点类是当前位置，如下所示；

import static java.lang.Math.*;

public class Point {

private static final double MIN_LONGITUDE = -180.0;
private static final double MAX_LONGITUDE = 180.0;
private static final double MIN_LATITUDE = -90.0;
private static final double MAX_LATITUDE = 90.0;
private static final double MEAN_EARTH_RADIUS = 6.371009e+6;

// TODO: Define fields for time, longitude, latitude and elevation

public static ZonedDateTime time = ZonedDateTime.now();
public static double longitude;
public static double latitude;
public static double elevation;


// TODO: Define a constructor



public Point(ZonedDateTime timestamp, double longitude, double latitude, double elevation) {

    if( longitude < MIN_LONGITUDE || longitude > MAX_LONGITUDE || latitude < MIN_LATITUDE || latitude > MAX_LATITUDE)
        throw new GPSException("Longitude or latitude is incorrect");


    this.longitude = longitude;
    this.latitude = latitude;
    this.elevation = elevation;

}

public Point() {
    this(time, -1.54853, 53.80462, 72.5);
}

// TODO: Define getters for the fields


public static ZonedDateTime getTime() {
    return time;
}

public static double getLongitude() {
    return longitude;
}

public static double getLatitude() {
    return latitude;
}

public static double getElevation() {
    return elevation;
}

// TODO: Define a toString() method that meets requirements
public String toString() {

    return "( " + longitude + ", " + latitude + " ),  " + elevation + " )";
}

然后有一个叫做Track的类，它是显示旅程的Points的集合。

class Track  {

public LinkedList<Point> Track = new LinkedList<Point>();

public void add(Object Point) {

    Track.add((Point) Point);
}


public Object get(int I) {

    return Track.get(I);

}

public Integer size() {

    int Size = Track.size();

    return Size;

}


public void readFile(String filename)
        throws IOException {

    int i = 0;

    ArrayList<String> textFile = new ArrayList<>();

    Scanner input = new Scanner(System.in);

    File file = new File(input.nextLine());

     input = new Scanner(filename);


    while (input.hasNext()) {
        String letter = input.next();
        textFile.add(i, letter);
        i++;
    }

    input.close();

    for (int j = 1; j < textFile.size(); j++) {


        ZonedDateTime times;
        double longitude = 0;
        double latitude;
        double elevation;

        String s = textFile.get(j);
        String[] half = s.split(",", 4);

        times = ZonedDateTime.parse(half[0]);
        longitude = Double.parseDouble((half[1]));
        latitude = Double.parseDouble((half[2]));
        elevation = Double.parseDouble((half[3]));

        Point point = new Point(times, longitude, latitude, elevation);

        Track.add(point);

    }

}


public String toString() {

    return "( " + Point.longitude + ", " + Point.latitude + " ), " + Point.elevation + " )";

}

}

 class Main {
    public static void main(String[] args) throws IOException {


    ZonedDateTime time = Point.getTime();

    Track track1 = new Track();


    Point point1 = new Point(time, -1.54853, 53.80462, 72.5);

    track1.add(point1);

    System.out.println("\n" + track1);
    System.out.println(point1.getElevation());

    track1.get(0).getElevation();


}

}

main的最后一行是给我一个错误无法解决的方法。它似乎是由getElevation引起的，但是我不确定如何解决它。任何帮助，将不胜感激。我已经在实际点上测试了get标高方法，并且效果很好。

Answer 1

因为您的呼叫track1.get(0)返回了Object而没有getElevation方法。您可能想在此处返回Point

class Track  {
    public Object get(int I) {

        return Track.get(I);

    }
}

此外，您的方法主体没有任何意义。

Answer 2

您必须强制转换get方法的结果：例如：

class Main {
    public static void main(String[] args) throws IOException {
    ZonedDateTime time = Point.getTime();
    Track track1 = new Track();
    Point point1 = new Point(time, -1.54853, 53.80462, 72.5);
    track1.add(point1);

    System.out.println("\n" + track1);
    System.out.println(point1.getElevation());

    if(track1.get(0) instanceof Point) { //Making sure we can cast the object
        (Point)(track1.get(0)).getElevation();
    }
}

无法解析方法getElevation（）

2 个答案: