5cf2fe009b
* Use lombok, reformat, and optimize the code * Fix merge conflicts and some sonar issues Co-authored-by: va1m <va1m@email.com>
80 lines
3.1 KiB
Java
80 lines
3.1 KiB
Java
/*
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* The MIT License
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* Copyright © 2014-2021 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.doubledispatch;
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import java.util.List;
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import lombok.extern.slf4j.Slf4j;
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/**
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* When a message with a parameter is sent to an object, the resultant behaviour is defined by the
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* implementation of that method in the receiver. Sometimes the behaviour must also be determined by
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* the type of the parameter.
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*
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* <p>One way to implement this would be to create multiple instanceof-checks for the methods
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* parameter. However, this creates a maintenance issue. When new types are added we would also need
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* to change the method's implementation and add a new instanceof-check. This violates the single
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* responsibility principle - a class should have only one reason to change.
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*
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* <p>Instead of the instanceof-checks a better way is to make another virtual call on the
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* parameter object. This way new functionality can be easily added without the need to modify
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* existing implementation (open-closed principle).
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*
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* <p>In this example we have hierarchy of objects ({@link GameObject}) that can collide to each
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* other. Each object has its own coordinates which are checked against the other objects'
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* coordinates. If there is an overlap, then the objects collide utilizing the Double Dispatch
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* pattern.
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*/
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@Slf4j
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public class App {
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/**
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* Program entry point.
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*
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* @param args command line args
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*/
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public static void main(String[] args) {
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// initialize game objects and print their status
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var objects = List.of(
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new FlamingAsteroid(0, 0, 5, 5),
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new SpaceStationMir(1, 1, 2, 2),
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new Meteoroid(10, 10, 15, 15),
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new SpaceStationIss(12, 12, 14, 14)
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);
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objects.forEach(o -> LOGGER.info(o.toString()));
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LOGGER.info("");
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// collision check
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objects.forEach(o1 -> objects.forEach(o2 -> {
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if (o1 != o2 && o1.intersectsWith(o2)) {
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o1.collision(o2);
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}
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}));
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LOGGER.info("");
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// output eventual object statuses
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objects.forEach(o -> LOGGER.info(o.toString()));
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LOGGER.info("");
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}
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}
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