单例模式根据实例化对象时机的不同分为两种：一种是饿汉式单例，一种是懒汉式单例。

私有的构造方法

指向自己实例的私有静态引用

以自己实例为返回值的静态的公有的方法

饿汉式单例

public class Singleton { private static Singleton singleton = new Singleton(); private Singleton(){} public static Singleton getInstance(){ return singleton; } }

懒汉式单例

public class Singleton { private static Singleton singleton; private Singleton(){} public static synchronized Singleton getInstance(){ if(singleton==null){ singleton = new Singleton(); } return singleton; } }

工厂方法模式代码

interface IProduct { public void productMethod(); } class Product implements IProduct { public void productMethod() { System.out.println("产品"); } } interface IFactory { public IProduct createProduct(); } class Factory implements IFactory { public IProduct createProduct() { return new Product(); } } public class Client { public static void main(String[] args) { IFactory factory = new Factory(); IProduct prodect = factory.createProduct(); prodect.productMethod(); } }

抽象工厂模式代码

interface IProduct1 { public void show(); } interface IProduct2 { public void show(); } class Product1 implements IProduct1 { public void show() { System.out.println("这是1型产品"); } } class Product2 implements IProduct2 { public void show() { System.out.println("这是2型产品"); } } interface IFactory { public IProduct1 createProduct1(); public IProduct2 createProduct2(); } class Factory implements IFactory{ public IProduct1 createProduct1() { return new Product1(); } public IProduct2 createProduct2() { return new Product2(); } } public class Client { public static void main(String[] args){ IFactory factory = new Factory(); factory.createProduct1().show(); factory.createProduct2().show(); } }

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