Custom Event generation and Handling

Question

HI all,
I am new to java. I have a dataset which changes dynamically and this dataset is responsible for some other dataset(s). So whenever the original dataset is modified, the other datasets based on this dataset should be updated automatically so as to preserve the consistency.
What I want to do is to write a custom event which is to be fired whenever the original dataset is modified and notify it to other datasets so as to ensure the consistency.
Any help in this regard is extremely appreciated.

Answer 1

HI Duffymo,
Here is my problem for better understanding:
I have a vector data in a NodePanel (this vector data originates from some other datastructure...but that is immaterial as we know that this data is an instance of that datastructure). This vectordata in NodePanel is responsible for another vectordata in SchedulePanel. The NodePanel and SchedulePanel are tabbedPanels in a tabbedframe. Whenever I update the vector data in NodePanel, the vector data in SchedulePanel needs to be updated.
The solution you gave me, taught me an insight of the event handling in Java.
I am quoting my source for your reference as I am unable to incorporate your idea into my project.
Event class:
import java.util.*;
public class VectorUpdateEvent extends EventObject
     public VectorUpdateEvent(Object source)
          super(source);
Interface to EventListener
public interface VectorUpdateListener
     public void eventVectorUpdated(VectorUpdateEvent event);
class EventGenerator
import java.util.*;
public class VectorUpdateEventIssuer
     implements EventListener
     public VectorUpdateEventIssuer()
          listListeners = new ArrayList();
     public synchronized void addVectorUpdateEventListener(VectorUpdateEvent l)
          listListeners.add(l);
     protected synchronized void removeVectorUpdateEventListener(VectorUpdateEvent l)
          listListeners.remove(listListeners.indexOf(l));
     protected void notifyVectorUpdateEvent(Object source)
          VectorUpdateEvent evt = new VectorUpdateEvent(source);
          Iterator itr = listListeners.iterator();
          while (itr.hasNext())
               ((VectorUpdateListener)itr.next()).eventVectorUpdated(evt);
     private ArrayList listListeners;
class where the event originates
class NodePanel
     extends JPanel
     implements ActionListener, ListSelectionListener
     /////////////Constructors/////////////////////////
     public NodePanel()
          addNodeButton = new JButton("Add Node");
          delNodeButton = new JButton("Delete Node");
          dumpNodeButton = new JButton("Dump Node");
          reloadNodeButton = new JButton("Reload Node");
          browseButton = new JButton("Browse Node");
          exitButton = new JButton("Exit");
          add(addNodeButton);
          add(delNodeButton);
          add(dumpNodeButton);
          add(reloadNodeButton);
          add(browseButton);
          add(exitButton);
          setButtonsEnabled(false);
          addNodeButton.addActionListener(this);
          delNodeButton.addActionListener(this);
          dumpNodeButton.addActionListener(this);
          reloadNodeButton.addActionListener(this);
          browseButton.addActionListener(this);
          exitButton.addActionListener(this);
          nodesVector = new Vector();
          nodesList = new JList(nodesVector);
          this.vectorNodeAttributes = new Vector();
          JScrollPane scrollPane = new JScrollPane(nodesList);
          add(scrollPane,BorderLayout.CENTER);
          nodesList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
          nodesList.addListSelectionListener(this);
     ////////////////Methods///////////////////////////
     /////////////Event valueChanged///////////////////
     public void valueChanged(ListSelectionEvent evt)
          JList source = (JList) evt.getSource();
          setButtonsEnabled(true);
          desiredNode = (String) source.getSelectedValue();
          if (desiredNode == null)
               setButtonsEnabled(false);
     //////////////Event actionPerformed////////////
     public void actionPerformed(ActionEvent evt)
          Object source = evt.getSource();
          if (source == addNodeButton)
               addNodeButtonClicked();
          else if (source == delNodeButton && desiredNode != null)
               deleteNodeButtonClicked();
          else if (source == dumpNodeButton && desiredNode != null)
               JFileChooser d = new JFileChooser();
               //d.setCurrentDirectory("");
               d.setFileFilter(new XMLFilter());
               int result = d.showSaveDialog(this);
          else if (source == reloadNodeButton && desiredNode != null)
               JFileChooser d1 = new JFileChooser();
               //d.setCurrentDirectory("");
               d1.setFileFilter(new XMLFilter());
               int result = d1.showOpenDialog(this);
               //String filename=d1.getSelectedFile().getName();
          if (source == browseButton && desiredNode != null)
               browseButtonClicked();
          else if (source == exitButton)
               System.exit(0);
     //////////Enables or Diables the Buttons////////
     private void setButtonsEnabled(boolean enable)
          delNodeButton.setEnabled(enable);
          dumpNodeButton.setEnabled(enable);
          reloadNodeButton.setEnabled(enable);
          browseButton.setEnabled(enable);
          private void deleteNodeButtonClicked()
          if (noFieldDlg != null)
               noFieldDlg.dispose();
          noFieldDlg = new NoFieldDialog("Delete the Node?");
          noFieldDlg.show();
          if (noFieldDlg.getDialogResult() == DialogResult.OK)
               int nodeToRemove=0;
               for (int i=0; i< vectorNodeAttributes.size(); i++)
                    if(((NodeAttributes)(vectorNodeAttributes.get(i))).getNodeName().compareTo(nodesList.getSelectedValue()) == 0)
                         nodeToRemove = i;
               vectorNodeAttributes.remove(nodeToRemove);
               nodesVector.removeElement(nodesList.getSelectedValue());
               this.nodesList.setListData(nodesVector);
               NodePanel.nodesPresent = nodesVector;
               updateStaticNodeList();
/*************** as soon as the NodePanel.nodesPresent is updated, the changes are to be reflected in the Schedule Panel ******************/
               VectorUpdateEvent e = new VectorUpdateEvent(this);
               VectorUpdateEventIssuer v = new VectorUpdateEventIssuer();
               v.addVectorUpdateEventListener(e);
               v.notifyVectorUpdateEvent(this);
     ///////////////Data Members////////////////////
     private JButton addNodeButton;
     private JButton delNodeButton;
     private JButton dumpNodeButton;
     private JButton reloadNodeButton;
     private JButton browseButton;
     private JButton exitButton;
     private String desiredNode;
     private OneFieldDialog oneFieldDlg = null;
     private NoFieldDialog noFieldDlg = null;
     private JList nodesList;
     private Vector nodesVector;
     private Vector vectorNodeAttributes;
     private static Vector nodesPresent = null;
} // end class NodePanel
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
import javax.swing.event.*;
////////////////Class SchedulePanel////////////////
class SchedulePanel extends JPanel
implements ActionListener, ListSelectionListener, VectorUpdateListener
     ////////////////Constructors//////////////////
     public SchedulePanel()
          addScheduleButton = new JButton("Add Schedule");
          delScheduleButton = new JButton("Delete Schedule");
          dumpScheduleButton = new JButton("Dump Schedule");
          reloadScheduleButton = new JButton("Reload Schedule");
          browseScheduleButton = new JButton("Browse Schedule");
          exitButton = new JButton("Exit");
          add(addScheduleButton);
          add(delScheduleButton);
          add(dumpScheduleButton);
          add(reloadScheduleButton);
          add(browseScheduleButton);
          add(exitButton);
          setButtonsEnabled(false);
          addScheduleButton.addActionListener(this);
          delScheduleButton.addActionListener(this);
          dumpScheduleButton.addActionListener(this);
          reloadScheduleButton.addActionListener(this);
          browseScheduleButton.addActionListener(this);
          exitButton.addActionListener(this);
          scheduleVector = new Vector();
          scheduleList = new JList(scheduleVector);
          this.vectorScheduleOperations = new Vector();
          JScrollPane scrollPane = new JScrollPane(scheduleList);
          add(scrollPane);
          scheduleList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
          scheduleList.addListSelectionListener(this);
          //updateEventListener = new VectorUpdateEventIssuer();
          //updateEventListener.addVectorUpdateEventListener(this);
     /////////////Methods///////////////////////
     ////////////Event valueChanged/////////////
     public void valueChanged(ListSelectionEvent evt)
          JList source = (JList)evt.getSource();
          setButtonsEnabled(true);
          desiredSchedule = (String)source.getSelectedValue();
          if (desiredSchedule == null)
               setButtonsEnabled(false);
     ////////////Event actionPerformed////////
     public void actionPerformed(ActionEvent evt)
          Object source = evt.getSource();
          if (source == addScheduleButton )
               addScheduleButtonClicked();
          else if (source==delScheduleButton && desiredSchedule!=null)
               deleteScheduleButtonClicked();
          else if (source == dumpScheduleButton && desiredSchedule!=null)
               JFileChooser d = new JFileChooser();
               d.setFileFilter(new XMLFilter());
               int result = d.showSaveDialog(this);
          else if (source == reloadScheduleButton && desiredSchedule!=null)
               JFileChooser d1 = new JFileChooser();
               d1.setFileFilter(new XMLFilter());
               int result = d1.showOpenDialog(this);
          else if (source == browseScheduleButton && desiredSchedule!=null)
               browseScheduleButtonClicked();
          else if (source == exitButton)
               System.exit(0);
     public void eventVectorUpdated(VectorUpdateEvent event)
          System.out.println("Hello! EventRaised");
     ///////////Data Members//////////////////
     private JButton addScheduleButton;
     private JButton delScheduleButton;
     private JButton dumpScheduleButton;
     private JButton reloadScheduleButton;
     private JButton browseScheduleButton;
     private JButton exitButton;
     private String desiredSchedule;
     private OneFieldDialog oneFieldDlg = null;
     private NoFieldDialog noFieldDlg = null;
     private JList scheduleList;
     private Vector scheduleVector;
     private Vector vectorScheduleOperations;
     private VectorUpdateEventIssuer updateEventListener;
} // end class SchedulePanel
I hope you understood my problem now. The NodeAttributes is a datastructure containing the node name and an associated table for that. THe ScheduleOperations is similar to the NodeAttributes but it contains a DefaultTableModel which inturn consists of a column which is filled with the list of current nodes available + their schedules.
I am sorry for my long posting.
Thanks once again in anticipation.