Swing

创建窗口

//1. Create the frame.
JFrame frame = new JFrame("FrameDemo");

//2. Optional: What happens when the frame closes?
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

//3. Create components and put them in the frame.
//...create emptyLabel...
frame.getContentPane().add(emptyLabel, BorderLayout.CENTER);

//4. Size the frame.
frame.pack();

//5. Show it.
frame.setVisible(true);

通过getContentPane获取到的顶层容器，返回的是Container，可以强制转化为JComponent使用，默认布局为BorderLayout。

更换布局

//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);

JPanel的默认布局为FlowLayout。