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State pattern added
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‎README.md

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@@ -8,6 +8,8 @@ I'm adding new samples from time to time.
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2. Chain Of Responsibility (COF) Pattern Java Examples 2
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3. Chain Of Responsibility (COF) Pattern Java Examples 3
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4. Interpreter Pattern Java Examples
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5. Singleton (EagerInitialization,as Enum,LazyInitialization,StaticBlockInitialization,ThreadSafe)
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6. State
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# Contribute
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‎src/io/github/mcaliman/patterns/singletion/EagerInitializationSingleton.java

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/*
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The MIT License (MIT)
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Copyright (c) 2015 Massimo Caliman
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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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The above copyright notice and this permission notice shall be included in all
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copies or substantial portions of the Software.
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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 THE
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SOFTWARE.
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*/
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package io.github.mcaliman.patterns.singletion;
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/**
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* Se l'applicazione ha sempre necessità di una istanza, o se il costo di
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* creazione della stessa non è troppo grande in termini di tempo e risorse, si
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* può utilizzare questa modalità che crea sempre un istanza.
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* <p>
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* L'Eager (impaziente!) Initialization Singleton è un singleton impaziente di inizializzare
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* la sua unica istanza possibile.
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*
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* @author Massimo Caliman
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*/
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public class EagerInitializationSingleton {
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/**
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* Istanza creata all'atto di caricamento della classe in memoria
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* quindi è thread-safe! Le convenzioni sono importanti
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* INSTANCE è scritto in maiscolo in quanto final e static.
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*/
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private final static EagerInitializationSingleton INSTANCE = new EagerInitializationSingleton();
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/**
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* Il singleton è utile se contiene o fa qualcosa, ecco quindi
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* un unica proprietà (dummy) accessive solo tramite setter e getter
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* appositi.
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*/
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private String property = "EagerInitializationSingleton property value.";
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/**
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* Il costruttore è privato, in quanto la creazione dell'istanza deve essere
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* controllata. Può avvenire solo all'interno della classe Singleton.
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*/
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private EagerInitializationSingleton() {
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System.out.println("Istanza di EagerInitializationSingleton creata! Questo messaggio non dovrà apparire più di una volta.");
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}
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/**
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* Unico punto di accesso al Singleton tramite metodo pubblico e statico.
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*
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* @return il Singleton
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*/
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public static EagerInitializationSingleton getInstance() {
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return INSTANCE;
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}
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public String getProperty() {
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return property;
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}
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public void setProperty(String property) {
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this.property = property;
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}
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}

‎src/io/github/mcaliman/patterns/singletion/EnumSingleton.java

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/*
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The MIT License (MIT)
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Copyright (c) 2015 Massimo Caliman
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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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The above copyright notice and this permission notice shall be included in all
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copies or substantial portions of the Software.
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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 THE
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SOFTWARE.
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*/
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package io.github.mcaliman.patterns.singletion;
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/**
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* Un modo originale (ed elegante) di realizzare un singleton con enum
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* Se sei interessato ad approfondire dai una lettura alla seconda edizione
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* di "Effective Java" di Joshua Bloch.
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* <p>
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* Questo approccio è funzionalmente equivalente al metodo con campo public (vedi gli altri
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* esempi),è più conciso e fornisce:
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* 1. Il meccanismo di serializzazione (gratuitamente)
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* 2. Una garanzia di protezione contro le istanze multiple
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* Ad oggi è comunque ancora relativamente sconosciuto e raramente utilizzato.
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*
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* @author Massimo Caliman
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*/
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public enum EnumSingleton {
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INSTANCE;
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public String getProperty() {
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return "EnumSingleton property value.";
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}
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}

‎src/io/github/mcaliman/patterns/singletion/LazyInitializationSingleton.java

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/*
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The MIT License (MIT)
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Copyright (c) 2015 Massimo Caliman
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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
11+
furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in all
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copies or substantial portions of the Software.
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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 THE
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SOFTWARE.
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*/
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package io.github.mcaliman.patterns.singletion;
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/**
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* Un singleton "pigro" (lazy). Inizializza (con tutti i relativi vantaggi)
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* la sua istanza solo quando necessario.
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*
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* @author Massimo Caliman
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*/
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public class LazyInitializationSingleton {
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private static LazyInitializationSingleton instance = null;
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/**
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* La proprietà (anche se è un dummy!) che giustifica il singleton (qualcosa
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* dovrà pur fare o comunicare.
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*/
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private String property = "LazyInitializationSingleton property value.";
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/**
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* Il costruttore privato impedisce l'istanza di oggetti da parte di classi esterne.
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*/
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private LazyInitializationSingleton() {
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System.out.println("Istanza di LazyInitializationSingleton creata! Questo messaggio non dovrà apparire più di una volta.");
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}
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/**
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* Metodo della classe impiegato per accedere al singleton. E'per ovvi motivi
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* sincronizzato (con due thread tentano di accedere si rischia la doppia istanza).
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*
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* @return il singleton.
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*/
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public static synchronized LazyInitializationSingleton getInstance() {
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if (instance == null) {
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instance = new LazyInitializationSingleton();
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}
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return instance;
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}
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public String getProperty() {
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return property;
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}
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public void setProperty(String property) {
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this.property = property;
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}
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}

‎src/io/github/mcaliman/patterns/singletion/SingletonPatternJavaExamples.java

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/*
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The MIT License (MIT)
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Copyright (c) 2015 Massimo Caliman
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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
10+
copies of the Software, and to permit persons to whom the Software is
11+
furnished to do so, subject to the following conditions:
12+
13+
The above copyright notice and this permission notice shall be included in all
14+
copies or substantial portions of the Software.
15+
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17+
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18+
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
19+
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20+
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21+
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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SOFTWARE.
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*/
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package io.github.mcaliman.patterns.singletion;
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/**
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* Chiamiamo i nostri vari singleton
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*
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* @author Massimo Caliman
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*/
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public class SingletonPatternJavaExamples {
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public static void main(String[] args) {
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System.out.println("EagerInitializationSingleton.getInstance().getProperty()=" + EagerInitializationSingleton.getInstance().getProperty());
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System.out.println("EnumSingleton.INSTANCE.getProperty()=" + EnumSingleton.INSTANCE.getProperty());
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System.out.println("LazyInitializationSingleton.getInstance().getProperty()=" + LazyInitializationSingleton.getInstance().getProperty());
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System.out.println("StaticBlockInitializationSingleton.getInstance().getProperty()=" + StaticBlockInitializationSingleton.getInstance().getProperty());
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System.out.println("ThreadSafeSingleton.getInstance().getProperty()=" + ThreadSafeSingleton.getInstance().getProperty());
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}
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}

‎src/io/github/mcaliman/patterns/singletion/StaticBlockInitializationSingleton.java

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/*
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The MIT License (MIT)
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Copyright (c) 2015 Massimo Caliman
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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
9+
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
10+
copies of the Software, and to permit persons to whom the Software is
11+
furnished to do so, subject to the following conditions:
12+
13+
The above copyright notice and this permission notice shall be included in all
14+
copies or substantial portions of the Software.
15+
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17+
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18+
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
19+
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20+
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21+
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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SOFTWARE.
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*/
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package io.github.mcaliman.patterns.singletion;
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/**
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* Singleton che realizza una forma di pre-elaborazione ( utile ad esempio per
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* il controllo degli errori).
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*
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* @author mcaliman
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*/
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public class StaticBlockInitializationSingleton {
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private final static StaticBlockInitializationSingleton INSTANCE;
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static {
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try {
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INSTANCE = new StaticBlockInitializationSingleton();
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} catch (Exception e) {
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throw new RuntimeException("error occurred.", e);
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}
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}
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private String property = "StaticBlockInitializationSingleton property value.";
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private StaticBlockInitializationSingleton() {
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//dovrebbe contiene qualcosa che potrebbe lanciare un eccezione...
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System.out.println("Istanza di StaticBlockInitializationSingleton creata! Questo messaggio non dovrà apparire più di una volta.");
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}
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public static StaticBlockInitializationSingleton getInstance() {
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return INSTANCE;
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}
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public String getProperty() {
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return property;
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}
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public void setProperty(String property) {
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this.property = property;
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}
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}

‎src/io/github/mcaliman/patterns/singletion/ThreadSafeSingleton.java

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/*
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The MIT License (MIT)
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Copyright (c) 2015 Massimo Caliman
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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
8+
in the Software without restriction, including without limitation the rights
9+
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
10+
copies of the Software, and to permit persons to whom the Software is
11+
furnished to do so, subject to the following conditions:
12+
13+
The above copyright notice and this permission notice shall be included in all
14+
copies or substantial portions of the Software.
15+
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17+
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18+
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
19+
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20+
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21+
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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SOFTWARE.
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*/
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package io.github.mcaliman.patterns.singletion;
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/**
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* Un altro tipo di singleton sicuro rispetto al multi-thread.
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*
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* @author Massimo Caliman
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*/
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public class ThreadSafeSingleton {
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/**
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* volatile garantisce che i cambiamenti siano visti immediatamente da tutti
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* gli altri thread
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*/
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private static volatile ThreadSafeSingleton instance = null;
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private String property = "ThreadSafeSingleton property value.";
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/**
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* Il costruttore private impedisce l'istanza di oggetti da parte di classi
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* esterne
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*/
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private ThreadSafeSingleton() {
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System.out.println("Istanza di ThreadSafeSingleton creata! Questo messaggio non dovrà apparire più di una volta.");
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}
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/**
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* Per accedere al singleton (vedi le altre classi di esempio e relativi
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* commenti).
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*
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* @return il singleton
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*/
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public static ThreadSafeSingleton getInstance() {
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if (instance == null) {
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/*
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* E' possibile rendere synchronized solo questa parte del metodo perché l'istanza
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* è di tipo volatile. Meno parte di un blocco di codice si riesce a rendere
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* synchronized meglio è...
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*/
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synchronized (ThreadSafeSingleton.class) {
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//non sono sicuro di essere ancora il primo thread ad accedere al metodo,
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//quindi ricontrollo
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if (instance == null) {
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instance = new ThreadSafeSingleton();
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}
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}
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}
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return instance;
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}
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public String getProperty() {
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return property;
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}
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public void setProperty(String property) {
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this.property = property;
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}
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}

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