/*File Event26.java Copyright 1997, R.G.Baldwin
This program is designed to be compiled and run under JDK 1.1

This is a bare-bones program that illustrates the ability to 
create, trap, and process events of new custom types.  

The output from the program for one particular run was:

Copyright 1997, R.G.Baldwin
customEventTrapped() method invoked on First NonVisualObject
Source of event was NonVisual[,0,0,0x0,invalid]
customEventTrapped() method invoked on Second NonVisualObject
Source of event was NonVisual[,0,0,0x0,invalid]

The program was tested using JDK 1.1 running under Win95.
*/
//==========================================================
import java.awt.*;
import java.awt.event.*;
import java.util.EventListener;
import java.util.EventObject;
//==========================================================

public class Event26 {
  public static void main(String[] args){
    new Event26();//instantiate an object of this type
  }//end main
//----------------------------------------------------------
  public Event26(){//constructor
    System.out.println("Copyright 1997, R.G.Baldwin");
    NonVisual firstNonVisualObject = new NonVisual(
                                   "First NonVisualObject");
    firstNonVisualObject.addCustomEventListener(
                            new CustomEventListenerClass());
    //create an event
    firstNonVisualObject.generateCustomEvent();

    NonVisual secondNonVisualObject = new NonVisual(
                                  "Second NonVisualObject");
    secondNonVisualObject.addCustomEventListener(
                            new CustomEventListenerClass());
    //The following statement causes the program to terminate
    // with the message
    // "No support for multiple Listener objects" because it
    // violates the restriction that this bare-bones program 
    // only allows one Listener object to be registered on 
    // each NonVisual object.  Therefore, the statement
    // has been disabled by making it a comment. It is 
    // included here for illustration purposes only.
    //secondNonVisualObject.addCustomEventListener(
                            new CustomEventListenerClass());
    //create an event
    secondNonVisualObject.generateCustomEvent();
    
  }//end constructor
}//end class Event26
//==========================================================

//Class to define a new type of event
class CustomEvent extends EventObject{
  String id;//instance variable for an object of this type
  //--------------------------------------------------------
  CustomEvent(Object obj, String id){//constructor
    super(obj);//pass the Object parameter to the superclass
    this.id = id;//save the String parameter
  }//end constructor
  //--------------------------------------------------------
  //method to return the saved String parameter
  String getCustomID(){
    return id;
  }//end getCustomID
}//end class CustomEvent
//==========================================================

//Define interface for the new type of event listener
interface CustomEventListener extends EventListener{
  void customEventTrapped(CustomEvent e);
}//
//==========================================================

//Listener class to respond to custom events
class CustomEventListenerClass 
                              implements CustomEventListener{
  public void customEventTrapped(CustomEvent e){
    System.out.println(
      "customEventTrapped() method invoked on " + 
                                            e.getCustomID());
    System.out.println("Source of event was " + 
                                              e.getSource());
  }//end customEventTrapped
}//end class CustomEventListenerClass
//==========================================================

//Class to create object capable of generating Custom events.
// Note:  This is a bare-bones version which can only support
// a single Listener object for the Custom event type.
class NonVisual extends Component {
  String ID; // The ID of this object
  //Reference to single Listener object
  CustomEventListenerClass customListener;
  //--------------------------------------------------------
  public NonVisual(String ID) {//Construct a NonVisual object
      this.ID = ID;
  }//end constructor
  //--------------------------------------------------------
  public void addCustomEventListener(
                          CustomEventListenerClass listener){
    //Do not attempt to add more than one Listener object.
    if(customListener == null) 
      customListener = listener;//one listener only
    else{
      System.out.println(
                 "No support for multiple Listener objects");
      //terminate on attempt to register multiple Listeners
      System.exit(0);
    }
  }//end addCustomEventListener()
  //--------------------------------------------------------
  public void generateCustomEvent() {
    customListener.customEventTrapped(
        new CustomEvent(this, ID));
  }//end generateCustomEvent
}//end class NonVisual
//=========================================================