how to convert jsonobject to json string in java

import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;

public class TestJSON {

	public static void main(String[] args) {

		JSONObject jObject = new JSONObject();

		jObject.put("EmployeeId", new Integer(121));
		jObject.put("Name", "Ramesh");
		jObject.put("Salary", new Double(15000.00));
		jObject.put("isPermanent", new Boolean(true));
		jObject.put("Nickname", null);
		
		//convert from JSONObject to JSON string
		String jsonText = jObject.toJSONString();

		System.out.println(jsonText);

		JSONParser parser = new JSONParser();
		
		//convert from JSON string to JSONObject
		JSONObject newJObject = null;
		try {
			newJObject = (JSONObject) parser.parse(jsonText);
		} catch (ParseException e) {
			e.printStackTrace();
		}

		System.out.println(newJObject.get("EmployeeId"));
		System.out.println(newJObject.get("Name"));
		System.out.println(newJObject.get("Salary"));
		System.out.println(newJObject.get("isPermanent"));
		System.out.println(newJObject.get("Nickname"));
	}
}