Write a Java code that returns the same result as the following JavaScript function : JSON.stringify;

public static String stringify(JsonObject js) {
    String str = "{";
    for (int i = 0; i < js.size(); i++) {
        Map.Entry<String, JsonValue> entry = js.get(i);
        str += entry.getKey() + ":" + entry.getValue();
        if (i != js.size() - 1) {
            str += ",";
        }
    }
    return str + "}";
}