The purpose is to realize the above place a button on a panel, a circle, click on the button, the color will change, in the round
But after I joined the implement, after listening to the click call function: the actionPerformed () will display frame marked red, connot resolve symbol frame, could you tell me how to modify?


Code:

 
The import javax.mail. Swing. *; 
import java.awt.*; 
Import the Java. The awt. Event. An ActionEvent; 
Import the Java. The awt. Event. ActionListener; 

The class MyDrawPanel extends JPanel {
Public void paintComponent (Graphics g) {
Graphics2D Graphics2D=g (Graphics2D); 
Int red=(int) (Math. The random () * 255); 
Int green=(int) (Math. The random () * 255); 
Int blue=(int) (Math. The random () * 255); 
Color startColor=new Color (red, green, blue); 

Red=(int) (Math. The random () * 255); 
Green=(int) (Math. The random () * 255); 
Blue=(int) (Math. The random () * 255); 
Color endColor=new Color (red, green, blue); 

GradientPaint GradientPaint=new GradientPaint (70, startColor, 150150, endColor); 
Graphics2D. SetPaint (gradientPaint);//the virtual brush painting gradually layer 
Graphics2D. FillOval,70,100,100 (70);//use the brush to fill the oval area 
} 
} 

Public class SimpleGUI implements ActionListener {
Public static void main (String [] args) {
SimpleGUI GUI=new SimpleGUI (); 
GUI. The go (); 
} 

Public void actionPerformed (an ActionEvent event) {
Frame. The repaint (); 
} 

//rewrite JPanel, join the style we need 

Public void the go () {
JFrame frame=new JFrame (); 
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);//set off or stop 

JButton button=new JButton (" do not click "); 
Button. AddActionListener (this); 
MyDrawPanel mypanel=new MyDrawPanel ();//create our myPanel object 

Frame. The add (BorderLayout. CENTER, mypanel);//add into the frame of the frame 
Frame. The add (BorderLayout. SOUTH, the button). 

Frame. The setSize (300300); 
frame.setVisible(true);//set the framework for visible 
} 

} 

Without the operation result of the interface:


The book instance