setContentPane(contentPane);
// contentPane.setLayout(new GridLayout());// 设置网格布局，默认是单行多列
contentPane.setLayout(new GridLayout(3, 3, 10, 10));// 设置网格布局 3行3列
for (int i = 0; i < 8; i++) {
JButton btn = new JButton("btn"+(i+1));
contentPane.add(btn);
}
}
}