JFrame 做一个简易的验证码

<!--<br /> <br /> Code highlighting produced by Actipro CodeHighlighter (freeware)<br /> http://www.CodeHighlighter.com/<br /> <br /> -->import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class ValidationCode extends JFrame implements ActionListener{
    private JButton productBtn;
    private JPanel downPanel;    
    public ValidationCode(){
        productBtn=new JButton("New Code");
        productBtn.addActionListener(this);
        productBtn.setSize(50,50);        
        downPanel=new JPanel();            
        downPanel.add(productBtn);        
        this.setTitle("Validation Code");        
        this.add(downPanel);    
    }
    public void actionPerformed(ActionEvent e){        
        this.repaint();
    }
    public void paint(Graphics g){        
        super.paint(g);
        String code="";
        char[] characters={'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z','a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','1','2','3','4','5','6','7','8','9','0'};
        char[] fourResult=new char[4];
        int index;
        for (int k=0;k<4;k++ ){
             index=(int)(Math.random()*62);
            fourResult[k]=characters[index];
        }
        for(int i=0;i<4;i++)
            code+=fourResult[i];           
        g.setColor(Color.RED);        
        g.drawString(code,100,100);
    }
    public static void main(String[] args){
        ValidationCode vc=new ValidationCode();
        vc.setBounds(300,300,200,200);
        vc.setVisible(true);
        vc.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}

运行结果：