public class LoginServerView extends JFrame
{
    public static void main(String args[]){
        LoginServerView login1=new LoginServerView();
    }  
    LoginServerView(){
        //处理登陆界面的北部
        JLabel jlb1=new JLabel(new ImageIcon("image/view1.gif"));
        
        
        //处理登录界面中间部分
        JPanel jpn1=new JPanel(new GridLayout(3,3));
        JLabel jlb3=new JLabel("账号：",JLabel.CENTER);
        JLabel jlb4=new JLabel("申请账号",JLabel.CENTER);
        jlb4.setForeground(Color.red);
        JLabel jlb5=new JLabel("密码：",JLabel.CENTER);
        JLabel jlb6=new JLabel("忘记密码",JLabel.CENTER);
        jlb6.setForeground(Color.red);
        JButton jbtn1=new JButton("登陆");
         JLabel jlb7=new JLabel();
        JButton jbtn2=new JButton("退出");
        JTextField jtx=new JTextField();
          JPasswordField jptx=new JPasswordField(15);
        
        jpn1.add(jlb3);
        jpn1.add(jtx);
        jpn1.add(jlb4);
        jpn1.add(jlb5);
        jpn1.add(jptx);
        jpn1.add(jlb6);   
        jpn1.add(jbtn1);
        jpn1.add(jlb7);
        jpn1.add(jbtn2);   
        //处理登录界面南部
        JLabel jlb2=new JLabel(new ImageIcon("image/view2.gif"));

         this.setSize(340, 240);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setVisible(true);
        this.add(jlb1,"North");
        this.add(jlb2,"South");
        this.add(jpn1,"Center");
       }
}

怎么样设置JButton的大小