Questions in ADF (ViewObjectImpl VS ViewObject) -- (Row VS ViewRowImpl)

Question

I have some confusion between (ViewObjectImpl VS ViewObject) -- (Row VS ViewRowImpl)
this is the code i mean this code from oracle slides
public void init() {
DBTransactionImpl trx = (DBTransactionImpl)getDBTransaction();
ApplicationModuleImpl am =(ApplicationModuleImpl)trx.getRootApplicationModule();
String user = am.getUserPrincipalName().toUpperCase();
System.out.println("The session user is: " + user);
ViewObjectImpl vo;
vo = getShoppingCart1();
String bindUser =(String)vo.getNamedWhereClauseParam("CurrentUser");
if (! user.equals(bindUser)) {
vo.setNamedWhereClauseParam("CurrentUser", user);
vo.executeQuery();
Row cart = vo.first();
if (cart == null) {
cart = vo.createRow();
cart.setAttribute("OrderDate",
((DBTransactionImpl)getDBTransaction()).getCurrentDbTime());
cart.setAttribute("OrderStatusCode", "CART");
vo.insertRow(cart);
this is another code from the slides
public void addItemToCart(Number productId) {
init();
ViewObject shoppingCartVO = getShoppingCart1();
assert shoppingCartVO != null;
ViewRowImpl shoppingCartRow =(ViewRowImpl)shoppingCartVO.first();
assert shoppingCartRow != null;
OrderEOImpl orderEO = (OrderEOImpl)shoppingCartRow.getEntity(0);
orderEO.addItemToOrder(productId);
in the first code getShoppingCart1(); returned ViewObjectImpl
in the second getShoppingCart1(); returned ViewObject
in the first code vo.first(); returned Row ;
in the seconde Returned ViewRowImpl ;
i want to know why and what is the difference
and in general when i use class and use classImpl what is the difference in general
and row and viewrowimpl
and why i wrote this tow lines
DBTransactionImpl trx = (DBTransactionImpl)getDBTransaction();
ApplicationModuleImpl am =(ApplicationModuleImpl)trx.getRootApplicationModule();
and what is the meaning of gerRootApplicaitoinModule(); what this will return

Answer 1

Briefly, ViewObject is an interface and ViewObjectImpl is (one of) its implementations.
Same with Row and ViewRowImpl.
You might need a good lesson in [object orientation and inheritance |http://en.wikipedia.org/wiki/Inheritance_%28computer_science%29]
and what is the meaning of gerRootApplicationModule(); what this will returnApplicationModules can be [ nested under one another|http://radio.weblogs.com/0118231/stories/2005/07/19/nestedApplicationModules.html] (to reuse business functionality).
[getRootApplicationModule()|http://download.oracle.com/docs/cd/E15051_01/apirefs.1111/e10653/oracle/jbo/server/ComponentObjectImpl.html#getRootApplicationModule%28%29] returns the topmost AM which is not nested under any other one.