import java.io.IOException;

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

class JsonDemo {
   public static void main(String[] args) throws IOException {
      JSONArray students = new JSONArray(); 
      students.add(new Student(1,"Robert")); 
      students.add(new Student(2,"Julia")); 

      System.out.println(students);     
   }
}
class Student implements JSONAware {
   int rollNo;
   String name;
   Student(int rollNo, String name){
      this.rollNo = rollNo;
      this.name = name;
   }
   @Override
   public String toJSONString() {
      StringBuilder sb = new StringBuilder();
      sb.append("{");
      sb.append("name");
      sb.append(":");
      sb.append("\"" + JSONObject.escape(name) + "\"");
      sb.append(",");
      sb.append("rollNo");
      sb.append(":");
      sb.append(rollNo);
      sb.append("}");
      return sb.toString();
   }    
}

[{name:"Robert",rollNo:1},{name:"Julia",rollNo:2}]