How to convert java object to json file in android?

Question

I have an object class like below and i want to convert it to a json string in android

public class Conversation {
    String idConversation; 
    String name; 
    String avatarPath;
    List<Message> listMessage; 

    public Conversation() {
     //constructor

    }
    public void setter(){...}
    public int getter(){...} 
}