Sometimes one object with multiple associated child objects, such as user and user address (assuming design are class), in defining the user class, will the image as a member of the user class, so that you can meet the needs of a request to all user data, but some features are not require users to address the child object, when the user has members in the class is redundant, in the transformation when the data is not convenient,
JavaScript can dynamically add class attribute, when necessary, without words, there is no, Java can achieve similar functionality?