Question

关于JAVA的JFrame和JPanel的问题,程序运行后,JPanel 无法显示. 代码如下:

public class SimpleGui {

JFrame frame ;
JButton button1;
JButton button2;
JLabel label;
public static void main (String [] args){
SimpleGui gui = new SimpleGui ();
gui.go();
}

public void go (){
frame = new JFrame ();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
button1 = new JButton ("egg");
button1.addActionListener(new Button1Listener ());

button2 = new JButton ("wawa");
button2.addActionListener(new Button2Listener ());

label = new JLabel ("i am wawa ");

MyDrawPanel drawpanel = new MyDrawPanel ();
frame.getContentPane().add(BorderLayout.SOUTH,button1);
frame.getContentPane().add(BorderLayout.EAST,button2);
frame.getContentPane().add(BorderLayout.CENTER,drawpanel);
frame.getContentPane().add(BorderLayout.WEST,label);
frame.setSize(300,300);
frame.setVisible(true);
}

class Button1Listener implements ActionListener {

@Override
public void actionPerformed(ActionEvent event) {
frame.repaint();

}
}
class Button2Listener implements ActionListener{

@Override
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
label.setText("HOHO");
}

}

}

类MyDrawPanel的代码如下:

class MyDrawPanel extends JPanel{
public void painComponent(Graphics g) {
Graphics2D g2d = (Graphics2D)g;
GradientPaint gradient = new GradientPaint(70,70,Color.blue,150,150,Color.orange);
g2d.setPaint(gradient);
g2d.fillOval(70, 70, 100, 100);
}

}

Answer 1

呵呵，我来帮你解决问题吧，其实非常非常简单，是不是有些粗心了？注意public void painComponent(Graphics g) 这句话 这个方法名字你打错了，自然不会执行了，不执行自然就不会画这个渐变的圆了，正确写法：public void paintComponent(Graphics g)即可搞定

Answer 2

明显的问题，这种布局需要东西南北中，你没有北？

Answer 3

呵呵，这个也不难的，我说个方法吧，
把圆 矩形等抽象出一个接口或类，
画图时，把图放到一个List里（LinkedList最快），
重写JFrame的 reprint()方法，在reprint()的时候把list里的图形添上去；