在学习工厂模式之前，我们先回顾下“简单工厂模式”；简单工厂模式就是问题了解决对象的创建问题；具体例子如下：
- 1.首先创建一个获取结果的抽象类，让所有的运算类继承它并实现具体的算法；
package com.zcbl.client.zcblsdk.factroymodel.simple;
/**
* Created by serenitynanian on 2018/2/9.
* 创建一个获取结果的抽象类
*/
public abstract class Operation {
public double numA ;
public double numB ;
public abstract double getResult();
}
- 2.创建具体的算法类，所有的算法类都必须实现Operation；
package com.zcbl.client.zcblsdk.factroymodel.simple;
/**
* Created by serenitynanian on 2018/2/9.
* 创建一个获取结果的抽象类
*/
public abstract class Operation {
public double numA ;
public double numB ;
public abstract double getResult();
}
package com.zcbl.client.zcblsdk.factroymodel.simple;
/**
* Created by serenitynanian on 2018/2/9.
* 具体的减法实现类
*/
public class OperationSub extends Operation {
@Override
public double getResult() {
double result = numA - numB;
return result;
}
}
package com.zcbl.client.zcblsdk.factroymodel.simple;
/**
* Created by serenitynanian on 2018/2/9.
* 具体的除法实现类
*/
public class OperationDiv extends Operation {
@Override
public double getResult() {
if (numB == 0) {
// throw new Exception("除数不能是零");
System.out.println("除数不能为零");
return 0.0;
}
double result = numA/numB;
return result;
}
}
- 3.创建具体的算法简单工厂类
package com.zcbl.client.zcblsdk.factroymodel.simple;
/**
* Created by serenitynanian on 2018/2/9.
* 简单的工厂运算类
*/
public class OperationFactory {
public static Operation createOperation(String operation) {
Operation ope = null ;
switch (operation) {
case "+":
ope = new OperationAdd();
break ;
case "-":
ope = new OperationSub();
break ;
case "*":
break ;
case "/":
ope = new OperationDiv();
break ;
}
return ope;
}
}
- 4.具体的调用如下：
package com.zcbl.client.zcblsdk.factroymodel.simple;
/**
* Created by serenitynanian on 2018/2/9.
*/
public class ClientTest {
public static void main(String[] args) {
Operation operation = OperationFactory.createOperation("+");
operation.numA = 6 ;
operation.numB = 2 ;
double result = operation.getResult();
System.out.println("----simple factory----result--->"+result);
}
}
简单工厂模式的最大的优点在于工厂类中包含了必要的逻辑判断，根据客户端的选择条件动态实例化相关的类，对于客户端来说，去除了与具体产品的依赖；
下面看下工厂模式
工厂方法模式（Factory Method）:定义一个用于创建对象的接口，让子类决定实例化哪一个类。工厂方法是一个类的实例延迟到其子类。
- 1.定义一个用于创建对象的接口
package com.zcbl.client.zcblsdk.factroymodel;
import com.zcbl.client.zcblsdk.factroymodel.simple.Operation;
/**
* Created by serenitynanian on 2018/2/9.
*/
public interface IFactory {
Operation createOperation();
}
- 2.创建具体的运算子类；
package com.zcbl.client.zcblsdk.factroymodel;
import com.zcbl.client.zcblsdk.factroymodel.simple.Operation;
import com.zcbl.client.zcblsdk.factroymodel.simple.OperationAdd;
/**
* Created by serenitynanian on 2018/2/9.
*/
public class AddFactory implements IFactory{
@Override
public Operation createOperation() {
return new OperationAdd();
}
}
package com.zcbl.client.zcblsdk.factroymodel;
import com.zcbl.client.zcblsdk.factroymodel.simple.Operation;
import com.zcbl.client.zcblsdk.factroymodel.simple.OperationSub;
/**
* Created by serenitynanian on 2018/2/9.
*/
public class SubFactory implements IFactory {
@Override
public Operation createOperation() {
return new OperationSub();
}
}
package com.zcbl.client.zcblsdk.factroymodel;
import com.zcbl.client.zcblsdk.factroymodel.simple.Operation;
import com.zcbl.client.zcblsdk.factroymodel.simple.OperationDiv;
/**
* Created by serenitynanian on 2018/2/9.
*/
public class DivFactory implements IFactory {
@Override
public Operation createOperation() {
return new OperationDiv();
}
}
- 3.具体的调用如下：
package com.zcbl.client.zcblsdk.factroymodel;
import com.zcbl.client.zcblsdk.factroymodel.simple.Operation;
/**
* Created by serenitynanian on 2018/2/9.
*/
public class FactoryMethodClientTest {
public static void main(String[] args) {
//如果需要创建不同的产品，使用不同的工厂类即可
IFactory iFactory = new AddFactory();
//以下都不变
Operation operation = iFactory.createOperation();
operation.numA = 9 ;
operation.numB = 2 ;
double res = operation.getResult();
System.out.println("-------factory method----result---->"+res);
}
}
总结：其实工厂方法模式实现时，客户端需要决定实例化哪一个工厂来实现运算类，选择判断的问题还是存在的，也就是说，工厂方法把简单工厂的内部逻辑判断移到了客户端代码来进行。你想要加功能，本来需要修改工厂类，而现在是修改客户端；这样整个工厂和产品体系没有修改，只是扩展需要的工厂类出来创建所需的实例，就完全符合了开放-封闭原则了；
简单工厂模式和工厂方法模式，它们二者都是集中封装了对象的创建过程，使得要更换对象时，不需要做大的改动就可实现，降低了客户程序与产品对象的耦合。
工厂方法模式是简单工厂模式的进一步抽象与推广。由于使用了多态性，工厂方法模式保持了简单工厂模式的优点，而且客服了它的缺点。但缺点是由于每加一个产品，就需要加一个产品工厂的类，增加了额外的开发量。
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