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QunzerQunzer
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add singleton pattern
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‎.gitignore‎

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# kdiff3 ignore
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*.orig
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# maven ignore
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target/
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# eclipse ignore
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.settings/
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.project
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.classpath
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# idea ignore
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.idea/
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*.ipr
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*.iml
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*.iws
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# temp ignore
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*.log
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*.cache
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*.diff
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*.patch
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*.tmp
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# system ignore
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.DS_Store
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Thumbs.db
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# package ignore (optional)
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# *.jar
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# *.war
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# *.zip
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# *.tar
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# *.tar.gz

‎designPatterns/pom.xml‎

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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>com.javalearning</groupId>
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<artifactId>javalearning</artifactId>
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<version>1.0-SNAPSHOT</version>
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</parent>
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<artifactId>designPatterns</artifactId>
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<packaging>jar</packaging>
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<name>designPatterns</name>
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<url>http://maven.apache.org</url>
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<properties>
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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</properties>
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<dependencies>
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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</dependency>
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</dependencies>
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</project>

‎designPatterns/src/main/java/com/javalearning/singleton/NotRightWorkSingleton.java‎

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package com.javalearning.singleton;
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/**
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* Created by renqun.yuan on 2015/10/14.
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*/
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public class NotRightWorkSingleton {
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private static NotRightWorkSingleton instance = null;
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private NotRightWorkSingleton() {
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}
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/**
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* In multiThread, it can't work
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*
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* @return
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*/
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public static NotRightWorkSingleton getInstance() {
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if (instance == null) {
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instance = new NotRightWorkSingleton();
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}
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return instance;
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}
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/**
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* 'new' may not a atomic operation,
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* instruct can be reorder
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* volatile used can be will work, see: SingletonLazyMode.java
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*
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* @return
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*/
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public static NotRightWorkSingleton getInstance1() {
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if (instance == null) {
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synchronized (SingletonLazyMode.class) {
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if (instance == null) {
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instance = new NotRightWorkSingleton();
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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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}

‎designPatterns/src/main/java/com/javalearning/singleton/SingletonEagerMode.java‎

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package com.javalearning.singleton;
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/**
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* Created by renqun.yuan on 2015/10/14.
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*/
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public class SingletonEagerMode {
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// when the class is loaded, the instance is initialized
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private static final SingletonEagerMode instance = new SingletonEagerMode();
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private SingletonEagerMode() {
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}
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public static SingletonEagerMode getInstance() {
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return instance;
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}
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}

‎designPatterns/src/main/java/com/javalearning/singleton/SingletonEagerMode1.java‎

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package com.javalearning.singleton;
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/**
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* Created by renqun.yuan on 2015/10/14.
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*/
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public class SingletonEagerMode1 {
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// when the getInstance method is invoked, the instance is initialized
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private static class SingletonInstanceHolder {
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private static final SingletonEagerMode1 INSTANCE = new SingletonEagerMode1();
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}
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private SingletonEagerMode1() {
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}
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public static SingletonEagerMode1 getInstance() {
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return SingletonInstanceHolder.INSTANCE;
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}
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}

‎designPatterns/src/main/java/com/javalearning/singleton/SingletonEnumMode.java‎

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package com.javalearning.singleton;
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/**
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* Created by renqun.yuan on 2015/10/14.
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*/
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public enum SingletonEnumMode {
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INSTANCE;
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}

‎designPatterns/src/main/java/com/javalearning/singleton/SingletonLazyMode.java‎

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package com.javalearning.singleton;
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/**
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* Created by renqun.yuan on 2015/10/14.
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*/
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public class SingletonLazyMode {
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private volatile static SingletonLazyMode instance = null;
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private SingletonLazyMode() {
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}
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// double-check
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public static SingletonLazyMode getInstance() {
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if (instance == null) {
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synchronized (SingletonLazyMode.class) {
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if (instance == null) {
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instance = new SingletonLazyMode();
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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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}

‎designPatterns/src/main/java/com/javalearning/singleton/package-info.java‎

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/**
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* Created by renqun.yuan on 2015/10/14.
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*/
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package com.javalearning.singleton;
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/**
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* Reference:
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* http://www.programcreek.com/2011/07/java-design-pattern-singleton/
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* http://coolshell.cn/articles/265.html
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* <p/>
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* Here is a simple use case. A country can have only one president
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* <p/>
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* Singleton Pattern
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* it should satisfy:
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* 1. private constructor - no other class can instantiate a new object.
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* 2.private reference - no external modification.
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* 3.public static method is the only place that can get an object.
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* <p/>
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* There are two modes:
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* 1. Eager Mode
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* 2. Lazy Mode
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* <p/>
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* Runtime.getRuntime() is singleton in Java
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* see: java.lang.Runtime
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**/
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‎designPatterns/src/test/java/com/javalearning/AppTest.java‎

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package com.javalearning;
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import junit.framework.Test;
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import junit.framework.TestCase;
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import junit.framework.TestSuite;
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/**
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* Unit test for simple App.
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*/
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public class AppTest
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extends TestCase {
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/**
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* Create the test case
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*
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* @param testName name of the test case
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*/
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public AppTest(String testName) {
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super(testName);
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}
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/**
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* @return the suite of tests being tested
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*/
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public static Test suite() {
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return new TestSuite(AppTest.class);
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}
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/**
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* Rigourous Test :-)
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*/
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public void testApp() {
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assertTrue(true);
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}
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}

‎pom.xml‎

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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>com.javalearning</groupId>
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<artifactId>javalearning</artifactId>
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<version>1.0-SNAPSHOT</version>
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<packaging>pom</packaging>
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<name>learningJava</name>
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<url>http://maven.apache.org</url>
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<modules>
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<module>designPatterns</module>
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</modules>
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<properties>
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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<junit.version>3.8.1</junit.version>
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</properties>
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<dependencyManagement>
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<dependencies>
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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<version>${junit.version}</version>
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<scope>test</scope>
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</dependency>
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</dependencies>
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</dependencyManagement>
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<build>
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<finalName>learningJava</finalName>
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<plugins>
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<plugin>
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<artifactId>maven-compiler-plugin</artifactId>
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<configuration>
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<source>1.7</source>
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<target>1.7</target>
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</configuration>
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</plugin>
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</plugins>
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</build>
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</project>

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