unable to add multiple values in extension in Object

[Rialakshmi]

HashMap<String, JsonElement> ext = new HashMap<>(); JsonElement je=new JsonPrimitive("location"));
ext.put(LOCATION,je);
ad.setExtensions(ext);
activity.setDefinition(ad);
statement.setObject(activity);

if I try to add one more value like classroom and classname to extension. I am getting error. Cant we add two or more values to extension? If we have some more values to be added to extension, then how can we add?