Java/Event/Event Queue

ActionEvent.getActionCommand()

 
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
class ButtonDemo implements ActionListener {
  JButton jbtnA = new JButton("Alpha");
  JButton jbtnB = new JButton("Beta");
  ButtonDemo() {
    JFrame jfrm = new JFrame("A Button Example");
    jfrm.setLayout(new FlowLayout());
    jfrm.setSize(220, 90);
    jfrm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    jbtnA.addActionListener(this);
    jbtnB.addActionListener(this);
    jfrm.add(jbtnA);
    jfrm.add(jbtnB);
    jfrm.setVisible(true);
  }
  public void actionPerformed(ActionEvent ae) {
    String ac = ae.getActionCommand();
    if (ac.equals("Alpha")) {
      if (jbtnB.isEnabled()) {
        System.out.println("Alpha pressed. Beta is disabled.");
        jbtnB.setEnabled(false);
      } else {
        System.out.println("Alpha pressed. Beta is enabled.");
        jbtnB.setEnabled(true);
      }
    } else if (ac.equals("Beta"))
      System.out.println("Beta pressed.");
  }
  public static void main(String args[]) {
    new ButtonDemo();
  }
}

Adding an InputMap to a Component

 
import javax.swing.InputMap;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.KeyStroke;
public class Main {
  public static void main(String[] argv) throws Exception {
    InputMap inputMap = new InputMap();
    inputMap.put(KeyStroke.getKeyStroke("F2"), "actionName");
    JButton component = new JButton("button");
    
    inputMap.setParent(component.getInputMap(JComponent.WHEN_FOCUSED));
    component.setInputMap(JComponent.WHEN_FOCUSED, inputMap);
  }
}

Event object has information about an event, that has happened.

 
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.DateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Locale;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class EventObject {
  public static void main(String[] args) {
    JFrame f = new JFrame();
    JButton ok = new JButton("Ok");
    ok.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent event) {
        Calendar cal = Calendar.getInstance();
        cal.setTimeInMillis(event.getWhen());
        Locale locale = Locale.getDefault();
        String s = DateFormat.getTimeInstance(DateFormat.SHORT, locale).format(new Date());
        if (event.getID() == ActionEvent.ACTION_PERFORMED)
          System.out.println(" Event Id: ACTION_PERFORMED");
        System.out.println(" Time: " + s);
        String source = event.getSource().getClass().getName();
        System.out.println(" Source: " + source);
        int mod = event.getModifiers();
        if ((mod & ActionEvent.ALT_MASK) > 0)
          System.out.println("Alt ");
        if ((mod & ActionEvent.SHIFT_MASK) > 0)
          System.out.println("Shift ");
        if ((mod & ActionEvent.META_MASK) > 0)
          System.out.println("Meta ");
        if ((mod & ActionEvent.CTRL_MASK) > 0)
          System.out.println("Ctrl ");
      }
    });
    f.add(ok);
    f.setSize(420, 250);
    f.setLocationRelativeTo(null);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setVisible(true);
  }
}

Event source and listener

 
import java.util.ArrayList;
import java.util.EventListener;
import java.util.EventObject;
abstract class TestEventSource {
  public abstract void addListener(TestEventListener l);
  public abstract void removeListener(TestEventListener l);
  public abstract void fireEvent(java.util.EventObject o);
  public void test() {
    addListener(new TestEventListener("A"));
    fireEvent(new java.util.EventObject(this));
  }
}
class TestEventListener implements EventListener {
  String id;
  public TestEventListener(String id) {
    this.id = id;
  }
  public void handleEvent(EventObject o) {
    System.out.println(id + " called");
    if (id.equals("C")) {
      ((TestEventSource) o.getSource()).removeListener(this);
    }
  }
}
public class Main extends TestEventSource {
  ArrayList listeners = new ArrayList();
  public void addListener(TestEventListener l) {
    listeners.add(l);
  }
  public void removeListener(TestEventListener l) {
    listeners.remove(l);
  }
  public void fireEvent(EventObject o) {
    for (int i = 0; i < listeners.size(); i++) {
      TestEventListener l = (TestEventListener) listeners.get(i);
      l.handleEvent(o);
    }
  }
  public static void main(String[] args) {
    Main pfles = new Main();
    pfles.test();
  }
}

int java.awt.event.WindowEvent.WINDOW_OPENED

 
import java.awt.AWTEvent;
import java.awt.Toolkit;
import java.awt.event.AWTEventListener;
import java.awt.event.ActionEvent;
import java.awt.event.ruponentEvent;
import java.awt.event.WindowEvent;
import javax.swing.AbstractAction;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
public class Main implements AWTEventListener {
  public void eventDispatched(AWTEvent evt) {
    if (evt.getID() == WindowEvent.WINDOW_OPENED) {
      ComponentEvent cev = (ComponentEvent) evt;
      if (cev.getComponent() instanceof JFrame) {
        System.out.println("event: " + evt);
        JFrame frame = (JFrame) cev.getComponent();
        loadSettings(frame);
      }
    }
  }
  public static void loadSettings(JFrame frame) {
    System.out.println("loading");
  }
  public static void saveSettings() {
    System.out.println("saving");
  }
  public static void main(String[] args) throws Exception {
    Toolkit tk = Toolkit.getDefaultToolkit();
    final Main main = new Main();
    tk.addAWTEventListener(main, AWTEvent.WINDOW_EVENT_MASK);
    final JFrame frame = new JFrame("");
    frame.setName("your frame");
    JMenuBar mb = new JMenuBar();
    JMenu menu = new JMenu("File");
    menu.add(new AbstractAction("Quit") {
      public void actionPerformed(ActionEvent evt) {
        try {
          main.saveSettings();
          System.exit(0);
        } catch (Exception ex) {
          System.out.println(ex);
        }
      }
    });
    mb.add(menu);
    frame.setJMenuBar(mb);
    frame.pack();
    frame.setVisible(true);
  }
}

JComponent.WHEN_IN_FOCUSED_WINDOW

 

import java.awt.event.ActionEvent;
import javax.swing.AbstractAction;
import javax.swing.Action;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.KeyStroke;
public class Main {
  public static void main(String[] argv) throws Exception {
    JButton component = new JButton();
    MyAction action = new MyAction();
    component.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke("F2"),
        action.getValue(Action.NAME));
  }
}
class MyAction extends AbstractAction {
  public MyAction() {
    super("my action");
  }
  public void actionPerformed(ActionEvent e) {
    System.out.println("hi");
  }
}

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

 
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
class ButtonListener implements ActionListener {
  public void actionPerformed(ActionEvent e) {
    JButton o = (JButton) e.getSource();
    String label = o.getText();
    System.out.println(label + " button clicked");
  }
}
public class MultipleSources {
  public static void main(String[] args) {
    JPanel panel = new JPanel();
    JButton close = new JButton("Close");
    close.addActionListener(new ButtonListener());
    JButton open = new JButton("Open");
    open.addActionListener(new ButtonListener());
    JButton find = new JButton("Find");
    find.addActionListener(new ButtonListener());
    JButton save = new JButton("Save");
    save.addActionListener(new ButtonListener());
    panel.add(close);
    panel.add(open);
    panel.add(find);
    panel.add(save);
    JFrame f = new JFrame();
    f.add(panel);
    f.setSize(400, 300);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setVisible(true);
  }
}

Register action

 
import java.awt.event.ActionEvent;
import javax.swing.AbstractAction;
import javax.swing.Action;
import javax.swing.JButton;
public class Main {
  public static void main(String[] argv) throws Exception {
    JButton component = new JButton();
    MyAction action = new MyAction();
    component.getActionMap().put(action.getValue(Action.NAME), action);
  }
}
class MyAction extends AbstractAction {
  public MyAction() {
    super("my action");
  }
  public void actionPerformed(ActionEvent e) {
    System.out.println("hi");
  }
}

Register several listeners for one event.

 
import java.awt.BorderLayout;
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.JPanel;
import javax.swing.JSpinner;
public class MultipleListeners {
  JLabel statusbar = new JLabel("0");
  JSpinner spinner = new JSpinner();
  static int count = 0;
  class ButtonListener1 implements ActionListener {
    public void actionPerformed(ActionEvent e) {
      Integer val = (Integer) spinner.getValue();
      spinner.setValue(++val);
    }
  }
  class ButtonListener2 implements ActionListener {
    public void actionPerformed(ActionEvent e) {
      statusbar.setText(Integer.toString(++count));
    }
  }
  public MultipleListeners() {
    JPanel panel = new JPanel();
    JButton add = new JButton("+");
    add.addActionListener(new ButtonListener1());
    add.addActionListener(new ButtonListener2());
    panel.add(add);
    panel.add(spinner);
    JFrame f = new JFrame();
    f.add(panel);
    f.add(statusbar, BorderLayout.SOUTH);
    f.setSize(300, 200);
    f.setLocationRelativeTo(null);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setVisible(true);
  }
  public static void main(String[] args) {
    new MultipleListeners();
  }
}

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");
    add(button);
    button.addActionListener(this);
  }
  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.");
    g.dispose();
  }
  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.setTitle("EventQueueTest");
    frame.setSize(300, 200);
    frame.addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent e) {
        System.exit(0);
      }
    });
    Container contentPane = frame.getContentPane();
    contentPane.add(new EventQueuePanel());
    frame.show();
  }
}

Using an inner ActionListener class.

 
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
public class InnerClass {
  class ButtonListener implements ActionListener {
    public void actionPerformed(ActionEvent e) {
      System.exit(0);
    }
  }
  public InnerClass() {
    JButton close = new JButton("Close");
    ButtonListener listener = new ButtonListener();
    close.addActionListener(listener);
    JFrame f = new JFrame();
    f.add(close);
    f.setSize(300, 200);
    f.setLocationRelativeTo(null);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setVisible(true);
  }
  public static void main(String[] args) {
    new InnerClass();
  }
}

void java.awt.Toolkit.addAWTEventListener(AWTEventListener listener, long eventMask)

 

import java.awt.AWTEvent;
import java.awt.Toolkit;
import java.awt.event.AWTEventListener;
import java.awt.event.ActionEvent;
import java.awt.event.ruponentEvent;
import java.awt.event.WindowEvent;
import javax.swing.AbstractAction;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
public class Main implements AWTEventListener {
  public void eventDispatched(AWTEvent evt) {
    if (evt.getID() == WindowEvent.WINDOW_OPENED) {
      ComponentEvent cev = (ComponentEvent) evt;
      if (cev.getComponent() instanceof JFrame) {
        System.out.println("event: " + evt);
        JFrame frame = (JFrame) cev.getComponent();
        loadSettings(frame);
      }
    }
  }
  public static void loadSettings(JFrame frame) {
    System.out.println("loading");
  }
  public static void saveSettings() {
    System.out.println("saving");
  }
  public static void main(String[] args) throws Exception {
    Toolkit tk = Toolkit.getDefaultToolkit();
    final Main main = new Main();
    tk.addAWTEventListener(main, AWTEvent.WINDOW_EVENT_MASK);
    final JFrame frame = new JFrame("");
    frame.setName("your frame");
    JMenuBar mb = new JMenuBar();
    JMenu menu = new JMenu("File");
    menu.add(new AbstractAction("Quit") {
      public void actionPerformed(ActionEvent evt) {
        try {
          main.saveSettings();
          System.exit(0);
        } catch (Exception ex) {
          System.out.println(ex);
        }
      }
    });
    mb.add(menu);
    frame.setJMenuBar(mb);
    frame.pack();
    frame.setVisible(true);
  }
}