對象java中的對象

Question

因此，我試圖使其成為當用戶創建新的PlaceInformation對象時，輸入的緯度和經度存儲在GeoLocation對象位置內。 顯然，在運行“客戶端”代碼時，首先初始化GeoLocation對象，並給出值0.0,0.0而不是用戶輸入的值。 如何使構造函數中的緯度和經度參數存儲在GeoLocation對象中？ 我嘗試了另一種方式，但有一些范圍問題。

public class PlaceInformation {
    private String name;
    private String tag;
    private String address;
    private double latitude;
    private double longitude;
    GeoLocation place = new GeoLocation(latitude, longitude);


    public PlaceInformation(String name, String address, String tag,
                        double latitude, double longitude) {
        this.name = name;
        this.address = address;
        this.tag = tag;
        this.latitude = latitude;
        this.longitude = longitude;
    }



    public String getName() {
        return name;
    }

    public String getAddress() {
        return address;
    }

    public String getTag() {
        return tag;
    }

    public String toString() {
        return name + ", " + address;
    }

    public double test() {
        return place.getLongitude();
    }

    public double distanceFrom(GeoLocation spot) {
        return spot.distanceFrom(place);
    }
}

Answer 1

在構造函數中實例化對象。

    public class PlaceInformation {
        private String name;
        private String tag;
        private String address;
        private double latitude;
        private double longitude;
        GeoLocation place;


        public PlaceInformation(String name, String address, String tag,
                            double latitude, double longitude) {
            place = new GeoLocation(latitude, longitude);
            this.name = name;
            this.address = address;
            this.tag = tag;
            this.latitude = latitude;
            this.longitude = longitude;
        }

        /* Rest of class omitted */
}

另請注意，您可能希望將該place設為私有。

Answer 2

如何在PlaceInformation構造函數中初始化place字段：

public class PlaceInformation {
    private String name;
    private String tag;
    private String address;
    private double latitude;
    private double longitude;
    GeoLocation place = null;


    public PlaceInformation(String name, String address, String tag,
                        double latitude, double longitude) {
        this.name = name;
        this.address = address;
        this.tag = tag;
        this.latitude = latitude;
        this.longitude = longitude;
        place = new GeoLocation(latitude, longitude);
    }

Answer 3

您應該將Geolocation聲明為私有字段。 然后，在構造函數中，您將創建該對象的新實例。 然后，其他方法將能夠“看到”地方變量。 總而言之，這不是“對象中的對象”，而是從一個對象到另一個對象的引用。

public class PlaceInformation {
    private String name;
    private String tag;
    private String address;
    private double latitude;
    private double longitude;
    private GeoLocation place;


    public PlaceInformation(String name, String address, String tag,
                        double latitude, double longitude) {
        this.name = name;
        this.address = address;
        this.tag = tag;
        this.latitude = latitude;
        this.longitude = longitude;
        this.place = new GeoLocation(latitude, longitude);
    }



    public String getName() {
        return name;
    }

    public String getAddress() {
        return address;
    }

    public String getTag() {
        return tag;
    }

    public String toString() {
        return name + ", " + address;
    }

    public double test() {
        return place.getLongitude();
    }

    public double distanceFrom(GeoLocation spot) {
        return spot.distanceFrom(place);
    }
}