Java 两个窗口间的传值

package jav;

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JTextField;
import javax.swing.WindowConstants;

public class ja9 {

    public static void main(String[] args) {
        Myframe mf = new Myframe();
        mf.setBounds(500, 400, 300, 200);
        mf.setVisible(true);
        mf.setLayout(new FlowLayout());

        JButton bu = new JButton("确定");
        mf.add(bu);
        
        bu.addActionListener(new ActionListener(){

            public void actionPerformed(ActionEvent arg0) {
                // TODO Auto-generated method stub
                Myframe ff=new Myframe();
                ff.setBounds(500, 450, 200, 100);
                ff.setVisible(true);
                ff.setLayout(new FlowLayout());
                JLabel la=new JLabel("请输入一个批号");
                JTextField tx=new JTextField(10);
                JButton bn=new JButton("确定");
                ff.add(la);
                ff.add(tx);
                ff.add(bn);
                bn.addActionListener(new ActionListener(){

                    public void actionPerformed(ActionEvent arg0) {
                        // TODO Auto-generated method stub
                    //mf.mm =tx.getText();
                    }
                    
                });
               
               
            }
            
        });

    }
}

class Myframe extends JFrame {
    public static String mm;

}