louzin
2 years ago
25 changed files with 539 additions and 0 deletions
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{ |
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"java.compile.nullAnalysis.mode": "automatic" |
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} |
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package com.louzin.java23.adapter; |
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public class Adapter extends Source implements Targetable { |
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@Override |
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public void method2() { |
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System.out.println("Targetable Method"); |
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} |
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} |
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package com.louzin.java23.adapter; |
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public class AdapterTester { |
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public static void main(String[] args) { |
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// Source source=new Source();
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// Wrapper wrapper=new Wrapper(source);
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// // Targetable targetable=new Adapter();
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// // targetable.method1();
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// // targetable.method2();
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// wrapper.method1();
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// wrapper.method2();
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Sourceable source1 = new SourceSub1(); |
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Sourceable source2 = new SourceSub2(); |
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source1.method1(); |
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source1.method2(); |
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source2.method1(); |
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source2.method2(); |
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} |
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} |
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package com.louzin.java23.adapter; |
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public class Source { |
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public void method1() { |
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System.out.println("Original Method"); |
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} |
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} |
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package com.louzin.java23.adapter; |
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public class SourceSub1 extends Wrapper2{ |
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public void method1(){ |
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System.out.println("Method1"); |
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} |
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} |
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package com.louzin.java23.adapter; |
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public class SourceSub2 extends Wrapper2{ |
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public void method2(){ |
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System.out.println("Method2"); |
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} |
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} |
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package com.louzin.java23.adapter; |
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public interface Sourceable { |
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public void method1(); |
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public void method2(); |
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} |
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package com.louzin.java23.adapter; |
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public interface Targetable { |
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//与Source类中的方法相同
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public void method1(); |
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//新类的方法
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public void method2(); |
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} |
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package com.louzin.java23.adapter; |
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public class Wrapper implements Targetable { |
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private Source source; |
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public Wrapper(Source source) { |
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super(); |
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this.source = source; |
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} |
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@Override |
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public void method1() { |
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source.method1(); |
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} |
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@Override |
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public void method2() { |
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System.out.println("Targetable Method!"); |
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} |
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} |
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package com.louzin.java23.adapter; |
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public abstract class Wrapper2 implements Sourceable{ |
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public void method1(){} |
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public void method2(){} |
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} |
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package com.louzin.java23.builder; |
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import java.util.ArrayList; |
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import java.util.List; |
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public class Builder { |
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private List<Sender> list = new ArrayList<Sender>(); |
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public void produceMailSender(int count){ |
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for(int i=0; i<count; i++){ |
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list.add(new MailSender()); |
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} |
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} |
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public void produceSmsSender(int count){ |
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for(int i=0; i<count; i++){ |
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list.add(new SmsSender()); |
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} |
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} |
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} |
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package com.louzin.java23.builder; |
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public class BuilderTest { |
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public static void main(String[] args) { |
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Builder builder = new Builder(); |
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builder.produceMailSender(10); |
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} |
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} |
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package com.louzin.java23.builder; |
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public class MailSender implements Sender{ |
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@Override |
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public void Send(){ |
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System.out.println("MailSender!"); |
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} |
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} |
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package com.louzin.java23.builder; |
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public interface Sender { |
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public void Send(); |
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} |
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package com.louzin.java23.builder; |
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public class SmsSender implements Sender{ |
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@Override |
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public void Send(){ |
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System.out.println("SmsSender!"); |
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} |
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} |
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package com.louzin.java23.decorator; |
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public class Decorator implements Sourceable{ |
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private Sourceable sourceable; |
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public Decorator(Sourceable sourceable) { |
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super(); |
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this.sourceable = sourceable; |
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} |
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@Override |
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public void method() { |
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System.out.println("before Decorator"); |
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sourceable.method(); |
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System.out.println("after Decorator"); |
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} |
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} |
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package com.louzin.java23.decorator; |
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public class DecoratorTest { |
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public static void main(String[] args) { |
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Sourceable sourceable=new Source(); |
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Sourceable objDecorator=new Decorator(sourceable); |
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objDecorator.method(); |
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} |
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} |
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package com.louzin.java23.decorator; |
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public class Source implements Sourceable{ |
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@Override |
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public void method() { |
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System.out.println("Original Method"); |
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} |
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} |
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package com.louzin.java23.decorator; |
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public interface Sourceable { |
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public void method(); |
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} |
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package com.louzin.java23.proxy; |
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public class Proxy implements Sourceable{ |
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private Source source; |
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public Proxy() { |
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super(); |
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this.source = new Source(); |
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} |
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@Override |
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public void method() { |
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before(); |
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source.method(); |
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after(); |
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} |
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private void after(){ |
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System.out.println("after"); |
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} |
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private void before(){ |
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System.out.println("before"); |
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} |
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} |
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package com.louzin.java23.proxy; |
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public class ProxyTester { |
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public static void main(String[] args) { |
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Sourceable sourceable=new Proxy(); |
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sourceable.method(); |
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} |
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} |
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package com.louzin.java23.proxy; |
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public class Source implements Sourceable{ |
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@Override |
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public void method() { |
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System.out.println("Original Method"); |
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} |
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} |
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package com.louzin.java23.proxy; |
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public interface Sourceable { |
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public void method(); |
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} |
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[JAVA]23种设计模式:工厂方法模式,抽象工厂模式,单例模式Ⅰ |
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设计模式(Design pattern)是一套被反复使用、多数人知晓的、经过分类编目的、代码设计经验的总结。使用设计模式是为了可重用代码、让代码更容易被他人理解、保证代码可靠性。 毫无疑问,设计模式于己于他人于系统都是多赢的,设计模式使代码编制真正工程化,设计模式是软件工程的基石,如同大厦的一块块砖石一样。项目中合理的运用设计模式可以完美的解决很多问题,每种模式在现在中都有相应的原理来与之对应,每一个模式描述了一个在我们周围不断重复发生的问题,以及该问题的核心解决方案,这也是它能被广泛应用的原因。 |
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<!-- more --> |
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# 设计模式的分类 |
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分为三大类: |
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- 创造型模式(五种) |
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> 工厂方法模式,抽象工厂模式,单例模式,建造者模式,原型模式 |
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- 结构型模式(七种) |
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> 适配器模式,装饰器模式,代理模式,外观模式,桥接模式,组合模式,享元模式 |
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- 行为型模式(十一种) |
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> 策略模式,模板方法模式,观察者模式,迭代子模式,责任链模式,命令模式,备忘录模式,状态模式,访问者模式,中介者模式,解释器模式 |
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补充:并发型模式,线程池模式 |
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## 1、工厂方法模式(Factory Method) |
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工厂方法模式分为三种 |
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### 1.1普通工厂方法模式 |
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建立一个工厂类,对实现了同一接口的一些类进行实例的创建: |
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```java |
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//共同接口 |
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public interface Sender { |
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public void Send(); |
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} |
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``` |
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```java |
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public class CommonFactoryMailSender implements Sender{ |
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@Override |
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public void Send() { |
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System.out.println("This is MailSender!"); |
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} |
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} |
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``` |
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```java |
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public class CommonFactorySmsSender implements Sender{ |
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@Override |
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public void Send() { |
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System.out.println("This is Sms Sender!"); |
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} |
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} |
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``` |
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建立工厂类: |
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```java |
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public class CommonFactorySendFactory { |
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public Sender producSender(String type){ |
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if("mail".equals(type)){ |
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return new CommonFactoryMailSender(); |
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}else if("sms".equals(type)){ |
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return new CommonFactorySmsSender(); |
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}else{ |
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System.out.println("类型错误!"); |
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return null; |
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} |
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} |
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} |
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``` |
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进行使用: |
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```java |
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public void testName() { |
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CommonFactorySendFactory factorySendFactory= new CommonFactorySendFactory(); |
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Sender sender=factorySendFactory.producSender("mail"); |
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sender.Send(); |
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}; |
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} |
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``` |
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### 1.2多个工厂方法模式 |
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对普通工厂方法模式进行改进,提供多个工厂方法模式,分别创建对象 |
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```java |
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public class MultipleFactorySendFactory { |
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public CommonFactoryMailSender produceSenderMail(){ |
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return new CommonFactoryMailSender(); |
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} |
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public CommonFactorySmsSender produceSenderSms(){ |
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return new CommonFactorySmsSender(); |
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} |
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} |
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``` |
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测试如下: |
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```java |
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public void test2(){ |
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MultipleFactorySendFactory factorySendFactory=new MultipleFactorySendFactory(); |
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Sender sender=factorySendFactory.produceSenderMail(); |
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sender.Send(); |
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} |
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``` |
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### 1.3静态工厂方法模式 |
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将多个工厂方法模式中的方法设置为静态,不需要创建实例,可以直接调用 |
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```java |
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public class StaticFactorySendFactory { |
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public static CommonFactoryMailSender procduceSenderMail(){ |
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return new CommonFactoryMailSender(); |
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} |
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public static CommonFactorySmsSender procduceSenderSms(){ |
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return new CommonFactorySmsSender(); |
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} |
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} |
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``` |
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测试如下: |
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```java |
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public void test3() { |
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Sender sender=StaticFactorySendFactory.procduceSenderSms(); |
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sender.Send(); |
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} |
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``` |
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### 1.4总结 |
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工厂方法模式适合大量需要创建,且具有共同的接口时,可以通过工厂方法模式进行创建 |
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对于以上三种,第一种通过字符串判断来创建对应的对象,第三种相对于第二种不需要实例化工厂类,一般情况下使用静态工厂方法模式 |
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## 2、抽象工厂模式(Abstract Factory) |
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工厂方法模式存在的问题是:类的创建依赖工厂类,如果想要扩展程序,就需要对工厂类进行修改,此时违背了闭包原则。从设计的角度,使用抽象工厂模式创建多个类,若需要新增功能直接增加新的工厂即可,同时无需修改之前的代码 |
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```java |
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public interface Sender { |
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public void Send(); |
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} |
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``` |
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继承并实现方法: |
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```java |
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//SmsSender |
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public class SmsSender implements Sender { |
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@Override |
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public void Send() { |
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System.out.println("SmsSender!"); |
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} |
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} |
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``` |
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```java |
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//MailSender |
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public class MailSender implements Sender { |
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@Override |
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public void Send() { |
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System.out.println("MailSender!"); |
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} |
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} |
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``` |
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实现共同接口: |
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```java |
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public interface Sender { |
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public void Send(); |
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} |
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``` |
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实现两个工厂类: |
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```java |
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public class SendSmsFactory implements Provider{ |
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@Override |
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public Sender produce() { |
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return new SmsSender(); |
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} |
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} |
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``` |
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```java |
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public class SendMailFactory implements Provider{ |
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@Override |
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public Sender produce(){ |
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return new MailSender(); |
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} |
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} |
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``` |
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测试如下: |
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```java |
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public void name() { |
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Provider provider=new SendMailFactory(); |
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com.louzin.java23.abstractfactory.Sender sender=provider.produce(); |
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sender.Send(); |
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} |
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``` |
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### 2.1总结 |
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若想添加一个新的功能,只需要做一个实现类实现Sender接口,同时创建一个工厂类实现Provider接口,无需改动现成的代码,扩展性较好 |
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## 3、单例模式(Singleton) |
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单例对象(Singleton)是一种常见的设计模式。在Java的应用中,能保证在一个JVM中只存在一个该对象的实例,这样的好处是: |
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- 限制某些繁琐类的建立,这类大型对象的创建是一笔很大的开销 |
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- 无需重复new,降低了系统内存的使用频率,减轻GC压力 |
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- 保证程序的核心流程只能创建一个 |
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|
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```java |
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public class SingletonDemo1 { |
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/* 持有私有静态实例,防止被引用,此处赋值为null,目的是实现延迟加载 */ |
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private static SingletonDemo1 instance = null; |
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|
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/* 私有构造方法,防止被实例化 */ |
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private SingletonDemo1() { |
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} |
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|
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/* 静态工程方法,创建实例 */ |
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public static SingletonDemo1 getInstance() { |
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if (instance == null) { |
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instance = new SingletonDemo1(); |
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} |
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return instance; |
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} |
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|
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/* 如果该对象被用于序列化,可以保证对象在序列化前后保持一致 */ |
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public Object readResolve() { |
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return instance; |
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} |
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} |
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``` |
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这个类可以满足单例的基本要求,但是若将其置于多线程环境,将会出现问题,我们会对`getInstance`方法加`synchronized`关键字: |
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~~~java |
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public static synchronized SingletonDemo1 getInstance() { |
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if (instance == null) { |
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instance = new SingletonDemo1(); |
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} |
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return instance; |
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} |
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~~~ |
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但是`synchronized`锁住的是这个对象,每次调用的时候都要加锁,非常影响性能。实际上,只有第一次创建的时候才需加锁,之后就不需要了: |
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```java |
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public static SingletonDemo1 getInstance() { |
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if (instance == null) { |
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synchronized (instance) { |
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if (instance == null) { |
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instance = new SingletonDemo1(); |
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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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``` |
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|
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这种方式很好理解,将加锁放在了内部,在调用的时候并不会加锁,只有在创建的时候才会加锁、 |
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**但是这种情况还是可能会出现问题**: |
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> 在Java指令中,**创建对象**和**赋值操作**是分开进行的,也就是说`instance = new SingletonDemo1()`是分开进行的,但是`JVM`并不能保证这两个操作的先后顺序,也就可能会出现JVM先为新的`SingletonDemo1`实例分配空间,然后直接赋值给`instance`,在此之后才进行初始化`SingletonDemo1`实例,此时便会出错 |
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|
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以下为例: |
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- A,B两个线程同时调用了这个类 |
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- A先判断完,进入`synchronized`块执行了`instance = new SingletonDemo1()` |
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- JVM内部优化机制,先分配了空白内存,并完成赋值,此时还未初始化这个实例 |
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- B判断`instance`不是`null`后离开了`synchronized`块,并将结果返回给调用方法 |
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- 调用方法抛出异常 |
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|
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解决方式如下: |
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```java |
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/* 此处使用一个内部类来维护单例 */ |
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private static class SingletonDemo1Factory { |
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private static SingletonDemo1 instance = new Singleton(); |
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} |
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/* 获取实例 */ |
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public static SingletonDemo1 getInstance() { |
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return SingletonDemo1.instance; |
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} |
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``` |
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单例模式使用内部类来维护单例的实现,`JVM`内部的机制能够保证当一个类被加载的时候,这个类的加载过程是线程互斥的,当我们第一次调用`getInstance`的时候,`JVM`能帮我们保证只会创建一次,并会把赋值给`instance`的内存初始化完成,以保证正常运行 |
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|
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**但是**如果在构造函数中抛出异常,实例将永远不会创建,也会造成出错,我们只能根据实际情况,选择最合适的应用场景 |
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|
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补充(分离创建和获取): |
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```java |
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public class SingletonTest { |
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private static SingletonTest instance = null; |
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//阻止实例化 |
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private SingletonTest() { |
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} |
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//分离创建和获取 |
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private static synchronized void syncInit() { |
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if (instance == null) { |
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instance = new SingletonTest(); |
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} |
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} |
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//获取对象 |
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public static SingletonTest getInstance() { |
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if (instance == null) { |
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syncInit(); |
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} |
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return instance; |
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} |
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//序列化一致性保证 |
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public Object readResolve() { |
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return instance; |
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} |
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} |
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``` |
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### 3.1影子实例 |
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采用"影子实例"的方法为单例对象的属性同步更新 |
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```java |
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public class SingletonTest { |
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|
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private static SingletonTest instance = null; |
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private Vector properties = null; |
||||
|
||||
public Vector getProperties() { |
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return properties; |
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} |
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|
||||
private SingletonTest() { |
||||
} |
||||
|
||||
private static synchronized void syncInit() { |
||||
if (instance == null) { |
||||
instance = new SingletonTest(); |
||||
} |
||||
} |
||||
|
||||
public static SingletonTest getInstance() { |
||||
if (instance == null) { |
||||
syncInit(); |
||||
} |
||||
return instance; |
||||
} |
||||
|
||||
public void updateProperties() { |
||||
SingletonTest shadow = new SingletonTest(); |
||||
properties = shadow.getProperties(); |
||||
} |
||||
} |
||||
``` 4、建造者模式(Builder) |
||||
工厂类模式服务于单个类,而建造者模式将各个类集中起来管理,用来创建复合对象,实际上就是抽象工厂类和`Test`的结合: |
||||
`Sender`接口,两个实现类`MailSender`和`SmsSender` |
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Reference in new issue