/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.doubledispatch;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.ArrayList;
import java.util.List;
/**
*
* When a message with a parameter is sent to an object, the resultant behaviour is defined by the implementation of
* that method in the receiver. Sometimes the behaviour must also be determined by the type of the parameter.
* <p>
* One way to implement this would be to create multiple instanceof-checks for the methods parameter. However, this
* creates a maintenance issue. When new types are added we would also need to change the method's implementation and
* add a new instanceof-check. This violates the single responsibility principle - a class should have only one reason
* to change.
* <p>
* Instead of the instanceof-checks a better way is to make another virtual call on the parameter object. This way new
* functionality can be easily added without the need to modify existing implementation (open-closed principle).
* <p>
* In this example we have hierarchy of objects ({@link GameObject}) that can collide to each other. Each object has its
* own coordinates which are checked against the other objects' coordinates. If there is an overlap, then the objects
* collide utilizing the Double Dispatch pattern.
*
*/
public class App {
private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
/**
* Program entry point
*
* @param args
* command line args
*/
public static void main(String[] args) {
// initialize game objects and print their status
List<GameObject> objects = new ArrayList<>();
objects.add(new FlamingAsteroid(0, 0, 5, 5));
objects.add(new SpaceStationMir(1, 1, 2, 2));
objects.add(new Meteoroid(10, 10, 15, 15));
objects.add(new SpaceStationIss(12, 12, 14, 14));
objects.stream().forEach(o -> LOGGER.info(o.toString()));
LOGGER.info("");
// collision check
objects.stream().forEach(o1 -> objects.stream().forEach(o2 -> {
if (o1 != o2 && o1.intersectsWith(o2)) {
o1.collision(o2);
}
}));
LOGGER.info("");
// output eventual object statuses
objects.stream().forEach(o -> LOGGER.info(o.toString()));
LOGGER.info("");
}
}