83 lines
3.7 KiB
Java
83 lines
3.7 KiB
Java
/**
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* The MIT License
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* Copyright (c) 2014-2016 Ilkka Seppälä
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* <p>
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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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* <p>
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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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* <p>
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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.dirtyflag;
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import java.util.List;
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import java.util.concurrent.Executors;
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import java.util.concurrent.ScheduledExecutorService;
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import java.util.concurrent.TimeUnit;
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/**
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*
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* This application demonstrates the <b>Dirty Flag</b> pattern. The dirty flag behavioral pattern allows you to avoid
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* expensive operations that would just need to be done again anyway. This is a simple pattern that really just explains
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* how to add a bool value to your class that you can set anytime a property changes. This will let your class know that
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* any results it may have previously calculated will need to be calculated again when they’re requested. Once the
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* results are re-calculated, then the bool value can be cleared.
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*
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* There are some points that need to be considered before diving into using this pattern:- there are some things you’ll
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* need to consider:- (1) Do you need it? This design pattern works well when the results to be calculated are difficult
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* or resource intensive to compute. You want to save them. You also don’t want to be calculating them several times in
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* a row when only the last one counts. (2) When do you set the dirty flag? Make sure that you set the dirty flag within
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* the class itself whenever an important property changes. This property should affect the result of the calculated
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* result and by changing the property, that makes the last result invalid. (3) When do you clear the dirty flag? It
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* might seem obvious that the dirty flag should be cleared whenever the result is calculated with up-to-date
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* information but there are other times when you might want to clear the flag.
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*
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* In this example, the {@link DataFetcher} holds the <i>dirty flag</i>. It fetches and re-fetches from <i>world.txt</i>
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* when needed. {@link World} mainly serves the data to the front-end.
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*/
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public class App {
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/**
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* Program execution point
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*/
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public void run() {
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final ScheduledExecutorService executorService = Executors.newSingleThreadScheduledExecutor();
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executorService.scheduleAtFixedRate(new Runnable() {
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@Override
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public void run() {
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World world = new World();
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List<String> countries = world.fetch();
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System.out.println("Our world currently has the following countries:-");
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for (String country : countries) {
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System.out.println("\t" + country);
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}
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}
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}, 0, 15, TimeUnit.SECONDS); // Run at every 15 seconds.
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}
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/**
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* Program entry point
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*
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* @param args
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* command line args
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*/
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public static void main(String[] args) {
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App app = new App();
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app.run();
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}
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}
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