Olá pessoal ,qual a diferença em adicionar um campo no formuário usando o getContentPane() ou diretamente no JFrame? :?: :?: :?:

Se eu entendi direito, se frame é um JFrame, os códigos e fazem a mesma coisa, uma vez que o método add() de JFrame chama o método add() do seu contentPane. É isso mesmo?

diferença em adicinar getContentPane e

Fiquei curioso com a sua pergunta e resolvi pesquisar, eis que no tutorial da sun tem a explicação

Tutorial Sun:

Adding Components to the Content Pane
Here’s the code that the preceding example uses to get a frame’s content pane and add the yellow label to it:
frame.getContentPane().add(yellowLabel, BorderLayout.CENTER);

As the code shows, you find the content pane of a top-level container by calling the getContentPane method. The default content pane is a simple intermediate container that inherits from JComponent, and that uses a BorderLayout as its layout manager.
It’s easy to customize the content pane ? setting the layout manager or adding a border, for example. However, there is one tiny gotcha. The getContentPane method returns a Container object, not a JComponent object. This means that if you want to take advantage of the content pane’s JComponent features, you need to either typecast the return value or create your own component to be the content pane. Our examples generally take the second approach, since it’s a little cleaner. Another approach we sometimes take is to simply add a customized component to the content pane, covering the content pane completely.

Note that the default layout manager for JPanel is FlowLayout; you’ll probably want to change it.

To make a component the content pane, use the top-level container’s setContentPane method. For example:
//Create a panel and add components to it.

JPanel contentPane = new JPanel(new BorderLayout());

contentPane.setBorder(someBorder);

contentPane.add(someComponent, BorderLayout.CENTER);

contentPane.add(anotherComponent, BorderLayout.PAGE_END);
topLevelContainer.setContentPane(contentPane);

Note: As a convenience, the add method and its variants, remove and setLayout have been overridden to forward to the contentPane as necessary. This means you can write
frame.add(child);
and the child will be added to the contentPane.

Note that only these three methods do this. This means that getLayout() will not return the layout set with setLayout().

Fonte: http://java.sun.com/docs/books/tutorial/uiswing/components/toplevel.html
Isso não cai na certificação se é esta a sua preocupação

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