菜鸟问题，关于swing的.先谢过了

public PlafPanel(){ metalButton=new JButton("Metal");
add(metalButton);
metalButton.addActionListener(this); textField=new JTextField(20);
add(textField);
}
public void actionPerformed(ActionEvent evt){
           textField.setText( "你好" );
         } //这个怎么写?
private JButton metalButton;
         private JTextField textField;