FirstFrame.java

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

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

public class FirstFrame extends JFrame implements ActionListener {

    public JTextField jtfFirst1 = null;
    private JButton jbFirst1 = null;
    private FirstFrame jframeFirst = null;

    public FirstFrame() {

        setTitle("Первое окно");
        setBounds(100, 100, 600, 200);

        GridLayout gl = new GridLayout(2, 1);
        setLayout(gl);

        jtfFirst1 = new JTextField();
        jtfFirst1.setEditable(false);

        jbFirst1 = new JButton();
        jbFirst1.setText("Получить текст");

        add(jtfFirst1);
        add(jbFirst1);

        jbFirst1.addActionListener(this);
    }

    @Override
    public void actionPerformed(ActionEvent arg0) {
        try {
            sfM();
        } catch (ClassNotFoundException | IOException e) {
            e.printStackTrace();
        }

        jtfFirst1.setText(jframeFirst.jtfFirst1.getText());

    }

    private void sfM() throws IOException, ClassNotFoundException {

        FileInputStream fis = new FileInputStream("text.ser");
        ObjectInputStream oin = new ObjectInputStream(fis);
        jframeFirst = (FirstFrame) oin.readObject();
        oin.close();
    }

    public static void main(String args[]) throws IOException, ClassNotFoundException {

        FileOutputStream fos = new FileOutputStream("text.ser");
        ObjectOutputStream oos = new ObjectOutputStream(fos);

        FirstFrame jframe = new FirstFrame();
        jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jframe.setVisible(true);

        oos.writeObject(jframe);
        oos.flush();
        oos.close();

        new SecondFrame();
    }

}