Use the Event queue to retrieve event : Event Queue « Event « Java

Use the Event queue to retrieve event

Use the Event queue to retrieve event
import java.awt.AWTEvent;
import java.awt.Container;
import java.awt.EventQueue;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class EventQueuePanel extends JPanel implements ActionListener {
  EventQueuePanel() {
    JButton button = new JButton("Draw line");

  public void actionPerformed(ActionEvent evt) {
    Graphics g = getGraphics();

    displayPrompt(g, "Click to chooose the first point");
    Point p = getClick();
    g.drawOval(p.x - 2, p.y - 2, 4, 4);
    displayPrompt(g, "Click to choose the second point");
    Point q = getClick();
    g.drawOval(q.x - 2, q.y - 2, 4, 4);
    g.drawLine(p.x, p.y, q.x, q.y);
    displayPrompt(g, "Done! Press button the start again.");

  public void displayPrompt(Graphics g, String s) {
    y += 20;
    g.drawString(s, 0, y);

  public Point getClick() {
    EventQueue eq = Toolkit.getDefaultToolkit().getSystemEventQueue();
    while (true) {
      try {
        AWTEvent evt = eq.getNextEvent();
        if (evt.getID() == MouseEvent.MOUSE_PRESSED) {
          MouseEvent mevt = (MouseEvent) evt;
          Point p = mevt.getPoint();
          Point top = getRootPane().getLocation();
          p.x -= top.x;
          p.y -= top.y;
          return p;
      } catch (InterruptedException e) {

  private int y = 60;
  public static void main(String[] args) {
    JFrame frame = new JFrame();
    frame.setSize(300, 200);
    frame.addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent e) {

    Container contentPane = frame.getContentPane();
    contentPane.add(new EventQueuePanel());;



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6.Multiple sources: A listener can be plugged into several sources.
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