Question

I have the following C# helper class which retrieves a Json String from a remote server and casts it to the type I need.

public class JsonHelper
{
    private JavaScriptSerializer serializer = new JavaScriptSerializer();

    public T GetValue<T>(string methodName, object param) where T : IConvertible
    {
        string result = GetJsonString(methodName, param);
        return (T)Convert.ChangeType(obj, typeof(T));
    }

    public T GetObject<T>(string methodName, object param) where T : new()
    {
        var result = GetValue<string>(methodName, param);
        return serializer.Deserialize<T>(result);
    }
}

–

// Usage:
bool value1 = GetValue<bool>(methodName, param);
int value2 = GetValue<int>(methodName, param);
double value3 = GetValue<double>(methodName, param);
User user = GetObject<User>(methodName, param);
List<User> users = GetObject<List<User>>(methodName, param);

Now I want to have the same functionality in a java programm. There are two points where I get stuck at the moment:

• Is this method call correct?

   public <T> T SendJsonPrimitiveRequest(String methodName, Object param)
      { 
          return null;
      }
  

And how do I restrict this generic method to only accept type parameters that can be casted from string.

• GetValue should be used for retrieving int, double, bool and string values which works great in C# by using Convert.ChangeType(…);
  Is this possible for Java or do I have to write methods like GetBool(), GetInt(), …?

Answer 1

Unfortunately, Java doesn’t have a built-in interface to describe conversion from a string. The closest is that some objects take a String in the constructor, or have a valueOf(String) static method. As there is no interface to declare this feature, it’s not going to be possible to use generics to restrict the type to objects that can be constructed from a string.

You can use generics with boxed types to provide a single GetValue method, but it requires also that you pass in the corresponding class of the type you want to retrieve, e.g.

  T <T> getValue(String methodName, Object param, Class<T> type)

Not very pretty, and coupled with the lack of a nice way to generically construct objects from strings, it is probably simplest (and more efficient with no boxing required) to create separate getInt(), getBool() methods.