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/*
 * Copyright 2011 Google Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.google.web.bindery.event.shared;

/**
 * Base Event object.
 * 
 * @param  interface implemented by handlers of this kind of event
 */
public abstract class Event {
  /**
   * Type class used to register events with an {@link EventBus}.
   * 
   * @param  handler type
   */
  public static class Type {
    private static int nextHashCode;
    private final int index;

    /**
     * Constructor.
     */
    public Type() {
      index = ++nextHashCode;
    }

    @Override
    public final int hashCode() {
      return index;
    }

    @Override
    public String toString() {
      return "Event type";
    }
  }

  private Object source;

  /**
   * Constructor.
   */
  protected Event() {
  }

  /**
   * Returns the {@link Type} used to register this event, allowing an
   * {@link EventBus} to find handlers of the appropriate class.
   * 
   * @return the type
   */
  public abstract Type getAssociatedType();

  /**
   * Returns the source for this event. The type and meaning of the source is
   * arbitrary, and is most useful as a secondary key for handler registration.
   * (See {@link EventBus#addHandlerToSource}, which allows a handler to
   * register for events of a particular type, tied to a particular source.)
   * 

* Note that the source is actually set at dispatch time, e.g. via * {@link EventBus#fireEventFromSource(Event, Object)}. * * @return object representing the source of this event */ public Object getSource() { return source; } /** * This is a method used primarily for debugging. It gives a string * representation of the event details. This does not override the toString * method because the compiler cannot always optimize toString out correctly. * Event types should override as desired. * * @return a string representing the event's specifics. */ public String toDebugString() { String name = this.getClass().getName(); name = name.substring(name.lastIndexOf(".") + 1); return "event: " + name + ":"; } /** * The toString() for abstract event is overridden to avoid accidently * including class literals in the compiled output. Use {@link Event} * #toDebugString to get more information about the event. */ @Override public String toString() { return "An event type"; } /** * Implemented by subclasses to to invoke their handlers in a type safe * manner. Intended to be called by {@link EventBus#fireEvent(Event)} or * {@link EventBus#fireEventFromSource(Event, Object)}. * * @param handler handler * @see EventBus#dispatchEvent(Event, Object) */ protected abstract void dispatch(H handler); /** * Set the source that triggered this event. Intended to be called by the * {@link EventBus} during dispatch. * * @param source the source of this event. * @see EventBus#fireEventFromSource(Event, Object) * @see EventBus#setSourceOfEvent(Event, Object) */ protected void setSource(Object source) { this.source = source; } }





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