Java String sorunu

 
  public void actionPerformed(ActionEvent e){  
  a = "kötü";  
  button.setText(a); 
   
  }  
  

 
   
  package jframe;  
   
   
  import java.awt.FlowLayout;  
  import java.awt.event.ActionEvent;  
  import java.awt.event.ActionListener;  
   
  import javax.swing.JButton;  
  import javax.swing.JFrame;  
   
  public class frame extends JFrame implements ActionListener{  
   
  private static final long serialVersionUID = 1L;  
   
  static String a = "iyi";  
  JButton button = null; 
   
   
  public static void main(String[] args){	 
  new frame().setVisible(true);  
  }  
   
   
  public frame(){  
   
  setSize(300,250);  
  setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
  button = new JButton(a);  
  add(button);  
  button.addActionListener(this);  
  setLayout(new FlowLayout());  
  }  
   
   
  public void actionPerformed(ActionEvent e){  
  button.setText("kötü");  
   
   
  }  
   
  }