import javax.swing.*;

public class TwoFrames extends JFrame {
    public TwoFrames() {
        super("First Frame");
        setSize(350, 100);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        SecondFrame two = new SecondFrame();
        setVisible(true);
        two.setVisible(true);
    }

    public static void main(String[] arguments) {
        TwoFrames tf = new TwoFrames();
    }
}

class SecondFrame extends JFrame {
    SecondFrame() {
        super("Second Frame");
        setSize(150, 80);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}