添加具有多個Arrylist的類對象

Question

嗨，我正在嘗試使用arrylists添加類對象，並需要以json格式顯示它。我將gson庫用於json格式，而iam tring將java對象綁定到jsonformat中，如下所示

" {"type": "record","name": "Doc","doc": "adoc","fields": [{"name": "id","type": "string"}, {"name": "user_friends_count","type": ["int", "null"]}]"

這些下面的類和主要方法

public class RootFields {
public String type;
public String name;
public String doc;

}

public class Fields {
public String name;
public String type;

}

這是我的主要方法

public class JavaToJson{


    public static void main(String[] args) {
        // TODO Auto-generated method stub      
RootFields root = new RootFields();
List<Fields> F2 = new ArrayList<Fields>();
Fields F1 = new Fields();
Fields Fields1 = new Fields();
Fields Fields2 = new Fields();
root.type = "record";
root.name = "Doc";
root.doc = "adoc";
F1.name = "id";
F1.type = "string";
Fields1.name = "user_friends_count";
Fields1.type = "int";
Fields2.name = "user_location";
Fields2.type = "int";
GsonBuilder builder = new GsonBuilder();
Gson gson = builder.create();

root.F2.add(F1);
System.out.println(gson.toJson(root));

    }

}

它顯示了我無法解決編譯錯誤F2或不是 F2中“ root.F2.add（F1）”中的字段的地方，我在哪里出錯，請提前幫忙。

Answer 1

您尚未在RootFields F2聲明為字段。 盡管據我了解，您應該使用List或數組，而不是每個Fields實例使用多個Fields 。

Answer 2

class RootFields {
    public String type;
    public String name;
    public String doc;
    List <Fields> filelds = new ArrayList<>();
}