12. 设计如下界面，在界面上方有一个标签“I’m a able”,中间有一个随机颜色的圆形，下方有两个按钮，点击点击“change lable”后标签改变为“ouch!”。点击“change circle”后圆改变颜色。用Java

下面是一个简单的Java程序实现该界面功能的代码：

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;

public class MyGUI extends JFrame implements ActionListener {
    private JLabel label;
    private JButton changeLabelButton;
    private JButton changeCircleButton;
    private JPanel panel;

    public MyGUI() {
        setTitle("MyGUI");
        setSize(400, 400);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);

        panel = new JPanel();
        panel.setLayout(new BorderLayout());

        label = new JLabel("I'm a able");
        label.setHorizontalAlignment(JLabel.CENTER);
        panel.add(label, BorderLayout.NORTH);

        CirclePanel circlePanel = new CirclePanel();
        panel.add(circlePanel, BorderLayout.CENTER);

        changeLabelButton = new JButton("Change Label");
        changeLabelButton.addActionListener(this);
        panel.add(changeLabelButton, BorderLayout.WEST);

        changeCircleButton = new JButton("Change Circle");
        changeCircleButton.addActionListener(this);
        panel.add(changeCircleButton, BorderLayout.EAST);

        add(panel);
        setVisible(true);
    }

    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == changeLabelButton) {
            label.setText("Ouch!");
        } else if (e.getSource() == changeCircleButton) {
            panel.remove(1);
            panel.add(new CirclePanel(), BorderLayout.CENTER);
            panel.revalidate();
            panel.repaint();
        }
    }

    private class CirclePanel extends JPanel {
        private Color color;

        public CirclePanel() {
            Random rand = new Random();
            color = new Color(rand.nextInt(256), rand.nextInt(256), rand.nextInt(256));
        }

        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.setColor(color);
            g.fillOval(100, 100, 200, 200);
        }
    }

    public static void main(String[] args) {
        MyGUI gui = new MyGUI();
    }
}

在这个程序中，使用了JFrame、JLabel、JButton和JPanel等Swing组件实现了界面的设计。其中，CirclePanel类继承自JPanel，实现了绘制一个随机颜色的圆形的功能。在按钮的监听器中，实现了改变标签和改变圆形颜色的功能。运行程序后，即可看到界面的效果。