我何时应该在Java中使用JFrame.add（component）和JFrame.getContentPane（）。add（component）

Question

它们之间是否有区别，是否有任何条件可以使用一种而不是另一种？

Answer 1

Both calls are the same. In Java 5, they changed jframe.add to forward calls to the content pane.

From the Java 5 release notes :

Lastly, after seven years, we've made jFrame.add equivalent to jFrame.getContentPane().add().

Also, see the javadocs .

Answer 2

如果您的问题仅涉及JFrame#add(JComponent)与JFrame.getContentPane()#add(JComponent) ，则没有区别，但是如果要更改fe BackGround，则取决于是否从JFrame#setBackground(Color)或从awt.Frame JFrame.getContentPane()#setBackground(Color)嵌套或继承方法...

Answer 3

From what I understand from Javadocs, JFrame.add calls the latter. It is a convenience method to get around the incompatibility between AWT's frame and Swings JFrame.

From javadocs for JFrame :

The JFrame class is slightly incompatible with Frame. Like all other JFC/Swing top-level containers, a JFrame contains a JRootPane as its only child. The content pane provided by the root pane should, as a rule, contain all the non-menu components displayed by the JFrame. This is different from the AWT Frame case. As a conveniance add 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. The content pane will always be non-null. Attempting to set it to null will cause the JFrame to throw an exception. The default content pane will have a BorderLayout manager set on it. Refer to RootPaneContainer for details on adding, removing and setting the LayoutManager of a JFrame.

Answer 4

add() will forward the work to addImpl() for which the JavaDoc of JFrame states the following:

By default, children are added to the contentPane instead of the frame.

Thus, both methods have the same basic behaviour, besides the fact that using getContentPane().add(...) is more explicit.

Note that you could alter the default behaviour for add (using setRootPaneCheckingEnabled(false) ), but I'm not sure you'd want to do that.