Erro Desconhecido

import java.awt.*; 
import java.awt.event.*;  
import javax.swing.*; 
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;

import javax.swing.BorderFactory;
import javax.swing.JFrame;


public class JButton extends JFrame implements ActionListener {
	
	public static void main (String arg[]){
		
	       
        JFrame Ex = new ClasseJButton();  
        Ex.setVisible(true);  
     }  
	JButton b1,b2;
	
	public JButton(){
		
	 setTitle("Isso e um teste");
	 setBounds(200,150,400,300);
	 
	 b1 = new JButton();
	 b1 = setText("Click here");
	 b1.setSize(100,25);
	 b1.setLocation(50,200);
	 b1.setBackground(Color.blue); 
	 b1.setForeground(Color.black);
	 b1.setFont(new Font("Sans Serif",Font.BOLD,14));
	 b1.setBorder(BorderFactory.createBevelBorder(1,Color.white,Color.black));  
     b1.setEnabled(true);  
     b1.addActionListener(this);  
     b1.setMnemonic(KeyEvent.VK_S);
     
     b2 = new JButton("Cadastrar");  
     b2.setSize(100,25);  
    b2.setLocation(200,200);  
      b2.setFont(new Font("ScriptS",Font.ITALIC,12));  
       b2.setBorder(BorderFactory.createLineBorder(Color.black,2));  
       b2.setEnabled(true);  
     b2.addActionListener(this);  
      b2.setMnemonic(KeyEvent.VK_C);// igual a utilizar ALT+C  
        
       getContentPane().setLayout(null);  
      getContentPane().add(b1);  
      getContentPane().add(b2); 
	 
	
	}
	
	public void actionPerformed(ActionEvent e){
	
		
		if (e.getSource ()==b1 ){
			System.exit(0);
			
		}
	
		
		if(e.getSource()==b2)   
	      {  
	           JFrame Ex = new JFrame();  
	           Ex.show();     
	      }      
		
	
		
	
	}
}