if(display_window) {
    if(this.displayInfo != null && this.displayInfo.isAlive()) {
        this.displayInfo.getFrame().dispose();
    }

    this.displayInfo = new DisplayInfo("title", window_text, 250, 50, 1000);
    this.displayInfo.start();
}

import javax.swing.*;
import java.awt.*;
public class DisplayInfo extends Thread {
    //title and text
    String title;
    String text;

    //size in pixels
    int width = 400;
    int height = 100;

    //time to display in ms
    int time = 3000;

    // The frame
    JFrame frame;

    //class infos
    static int instances = 0;
    static DisplayInfo instance;

    public DisplayInfo(String title, String text, int width, int height, int time) {
        if(instances>0) {
            instance.stopInstance();
        }
        ++instances;
        instance = this;
        this.title = title;
        this.text = text;
        this.width = width;
        this.height = height;
        this.time = time;
    }

    public void run() {
        //Create and set up the window.
        this.frame = new JFrame(title);
        this.frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.frame.setUndecorated(true); //removes the borders

        //add text to the frame
        JLabel label = new JLabel(instances+" - "+text, JLabel.CENTER);
        label.setForeground(new Color(0xBB, 0xBB, 0xBB));
        this.frame.getContentPane().add(label);

        //set size
        this.frame.setSize(width, height);

        //get screen size
        Toolkit toolkit = Toolkit.getDefaultToolkit();
        Dimension screenSize = toolkit.getScreenSize();

        //Calculate the frame location
        int x = (screenSize.width - frame.getWidth()) / 2;
        int y = ((screenSize.height - frame.getHeight()) / 3) * 2;

        //color
        this.frame.getContentPane().setBackground(new Color(0x33, 0x33, 0x33));

        //Display the window.
        this.frame.setLocation(x ,y);
        this.frame.setVisible(true);

        //wait
        try {
            Thread.currentThread().sleep(time);
        } catch(InterruptedException ie) { }

        //close
        this.frame.dispose();
    }

    public void stopInstance() {
        --instances;
        this.stop();
    }

    public JFrame getFrame() {
        return this.frame;
    }
}