[FIXED] JSON and Generics in Java - Type safety warning

Issue

I have some data stored in Java elements and I need to return it in a given format - JSONObject. While my implementation works fine, I'm still getting a warning message from eclipse (Version: Juno Service Release 2):

"Type safety: The method put(Object, Object) belongs to the raw type HashMap. References to generic type HashMap should be parameterized"

This is my code:

public interface Element {...}

public abstract class AbstractElement implements Element {...}

public final class Way extends AbstractElement {...}

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import org.json.simple.JSONArray;
import org.json.simple.JSONObject;

public class WayToJsonConverter{
    ...
    public JSONObject wayToJson(){
        JSONObject obj = new JSONObject();
        obj.put("id",way.getId());
        ...
        return obj;
    }
    ...
}

The problematic line is : obj.put("id",way.getId());

Is there a way to solve this issue other then adding @SuppressWarnings("unchecked")?

Solution

What is your JSONObject, does it inherit from HashMap? If does, the warn probably means that your should declare the JSONObject instance as follows:

JSONObject<String,Object> obj=new JSONObject<String,Object>();

Updated: Look at the definition of the JSONObject:

public class JSONObject extends HashMap

it extends HashMap but doesn't support parameter type, if its definition is

public class JSONObject<K,V> extends HashMap<K,V>

then we could write

JSONObject<String,Object> obj=new JSONObject<String,Object>();

and the put method will no longer generate the warning

Answered By - ltebean