设计模式之工厂模式

首先需要区分简单工厂模式、工厂模式、抽象工厂模式

       简单工厂模式、工厂模式、抽象工厂模式都属于创建型模式，主要功能是帮助我们将对象的实例化部分抽取出来，优化系统架构，增强系统可扩展性。

       （1）简单工厂模式可以实现产品类实例代码与客户端代码分离，但是不符合开闭原则（对修改关闭，对扩展开放）。

public interface Product {}public class ProductA implements Product {public ProductA() {System.out.println("ProdutA");}}public class ProductB implements Product {public ProductB() {System.out.println("ProductB");}}public class SimpleFactory {public Product create(String name){switch (name) {case "ProductA":return new ProductA();case "ProductB":return new ProductB();default:return null;}}} public class SimpleFactoryTest {public static void main(String[] args) {new SimpleFactory().create("ProductA");new SimpleFactory().create("ProductB");}}

（2）工厂模式中，对应的工厂类可以生产对应的产品类，满足了开闭原则，无论增加多少产品类，只需要增加相应的工厂类就可以了，而不用修改原来的工厂类。

缺点是，如果产品很多，那么就要生成很多的工厂类。

public interface Product {}public class ProductA implements Product {public ProductA() {System.out.println("ProdutA");}}public class ProductB implements Product {public ProductB() {System.out.println("ProductB");}}public interface Factory {public Product createFactoryProduct() throws Exception;}public class FactoryB implements Factory {@Overridepublic Product createFactoryProduct() throws Exception {// TODO Auto-generated method stubreturn new ProductB();}}public class FactoryA implements Factory {@Overridepublic Product createFactoryProduct() throws Exception {// TODO Auto-generated method stubreturn new ProductA();}}public class MainTest {public static void main(String[] args) throws Exception {Factory factory;factory = new FactoryA();factory.createFactoryProduct();factory = new FactoryB();factory.createFactoryProduct();}}

（3）抽象工厂是应对产品族概念的。比如说，每个汽车公司可能要同时生产轿车，货车，客车，那么每一个工厂都要有创建轿车，货车和客车的方法。

应对产品族概念而生，增加新的产品线很容易，但是无法增加新的产品。

public interface ProductA {public void operationA();}public class ProductA1 implements ProductA {public ProductA1() {}@Overridepublic void operationA() {System.out.println("ProductA1");}}public class ProductA2 implements ProductA {public ProductA2() {}@Overridepublic void operationA() {System.out.println("ProductA2");}}public interface ProductB {public void operationB();}public class ProductB1 implements ProductB {public ProductB1() {}@Overridepublic void operationB() {System.out.println("ProductB1");}}public class ProductB2 implements ProductB {public ProductB2() {}@Overridepublic void operationB() {System.out.println("ProductB2");}}public interface AbstractFactory {public ProductA getProductA(String name);public ProductB getProductB(String name);}public class AbstractFactoryA implements AbstractFactory {@Overridepublic ProductA getProductA(String name) {switch (name) {case "ProductA1":return new ProductA1();case "ProductA2":return new ProductA2();default:return null;}}@Overridepublic ProductB getProductB(String name) {// TODO Auto-generated method stubreturn null;}}public class AbstractFactoryB implements AbstractFactory {@Overridepublic ProductA getProductA(String name) {return null;}@Overridepublic ProductB getProductB(String name) {switch (name) {case "ProductB1":return new ProductB1();case "ProductB2":return new ProductB2();default:return null;}}}public class FacoryProducer {public AbstractFactory getAbstractFactory(String name){if("AbstractFactoryA".equals(name)){return new AbstractFactoryA();}else if("AbstractFactoryB".equals(name)){return new AbstractFactoryB();}else {return null;}}}