Go和Java实现工厂方法模式
Go和Java实现工厂方法模式
本文通过计算器案例来说明工厂方法模式的使用，使用Go语言和Java语言实现。
1、工厂方法模式
工厂方法模式是最常用的设计模式之一，这种类型的设计模式属于创建型模式，它提供了一种创建对象的最佳方
式。
在工厂方法模式中，我们在创建对象时不会对客户端暴露创建逻辑，并且是通过使用一个共同的接口来指向新创建
的对象。
-
意图：定义一个创建对象的接口，让其子类自己决定实例化哪一个工厂类，工厂方法模式使其创建过程延迟到
子类进行。
-
主要解决：主要解决接口选择的问题。
-
何时使用：我们明确地计划不同条件下创建不同实例时。
-
如何解决：让其子类实现工厂接口，返回的也是一个抽象的产品。
-
关键代码：创建过程在其子类执行。
-
应用实例：1、您需要一辆汽车，可以直接从工厂里面提货，而不用去管这辆汽车是怎么做出来的，以及这个
汽车里面的具体实现。 2、Hibernate 换数据库只需换方言和驱动就可以。
-
优点：1、一个调用者想创建一个对象，只要知道其名称就可以了。 2、扩展性高，如果想增加一个产品，只
要扩展一个工厂类就可以。 3、屏蔽产品的具体实现，调用者只关心产品的接口。
-
缺点：每次增加一个产品时，都需要增加一个具体类和对象实现工厂，使得系统中类的个数成倍增加，在一定
程度上增加了系统的复杂度，同时也增加了系统具体类的依赖。这并不是什么好事。
-
使用场景：1、日志记录器：记录可能记录到本地硬盘、系统事件、远程服务器等，用户可以选择记录日志到
什么地方。 2、数据库访问，当用户不知道最后系统采用哪一类数据库，以及数据库可能有变化时。 3、设计
一个连接服务器的框架，需要三个协议，“POP3”、“IMAP”、“HTTP”，可以把这三个作为产品类，共同实现一
个接口。
-
注意事项：作为一种创建类模式，在任何需要生成复杂对象的地方，都可以使用工厂方法模式。有一点需要注
意的地方就是复杂对象适合使用工厂方法模式，而简单对象，特别是只需要通过 new 就可以完成创建的对
象，无需使用工厂方法模式。如果使用工厂方法模式，就需要引入一个工厂类，会增加系统的复杂度。
-
适用性：1、当一个类不知道它所必须创建的对象的类的时候。2、当一个类希望由它的子类来指定它所创建
的对象的时候。3、当类将创建对象的职责委托给多个帮助子类中的某一个，并且类希望将哪一个帮助子类是
代理者这一信息局部化的时候。
简单说工厂方法模式就是为了提供代码结构的扩展性，屏蔽每⼀个功能类中的具体实现逻辑，让外部可以更加简单
的只是知道调⽤即可，同时这也是去掉众多 ifelse 的⽅式。
2、Go实现简单计算器
下面实现一个简单的计算器，包含简单的加减乘除功能。
package factory
// 这里实现一个简单的计算器
// 计算接口,包含计算数的设置和结果的计算
type Operation interface {
// 设置进行计算的两个数
SetNumberA(float64)
SetNumberB(float64)
// 计算
Calculate() (float64, error)
}
package factory
// ============加法===========
type AddOperation struct {
// 包含两个操作数
numberA float64
numberB float64
}
func (addOperation *AddOperation) Calculate() (float64, error) {
return addOperation.numberA + addOperation.numberB, nil
}
func (addOperation *AddOperation) SetNumberA(numberA float64) {
addOperation.numberA = numberA
}
func (addOperation *AddOperation) SetNumberB(numberB float64) {
addOperation.numberB = numberB
}
package factory
// ============减法============
type SubOperation struct {
// 包含两个操作数
numberA float64
numberB float64
}
func (subOperation *SubOperation) Calculate() (float64, error) {
return subOperation.numberA - subOperation.numberB, nil
}
func (subOperation *SubOperation) SetNumberA(numberA float64) {
subOperation.numberA = numberA
}
func (subOperation *SubOperation) SetNumberB(numberB float64) {
subOperation.numberB = numberB
}
package factory
// ============乘法============
type MulOperation struct {
// 包含两个操作数
numberA float64
numberB float64
}
func (mulOperation *MulOperation) Calculate() (float64, error) {
return mulOperation.numberA * mulOperation.numberB, nil
}
func (mulOperation *MulOperation) SetNumberA(numberA float64) {
mulOperation.numberA = numberA
}
func (mulOperation *MulOperation) SetNumberB(numberB float64) {
mulOperation.numberB = numberB
}
package factory
import "errors"
// ============除法============
type DivOperation struct {
// 包含两个操作数
numberA float64
numberB float64
}
func (divOperation *DivOperation) Calculate() (float64, error) {
if divOperation.numberB == 0 {
return -1, errors.New("被除数不能为0")
} else {
return divOperation.numberA / divOperation.numberB, nil
}
}
func (divOperation *DivOperation) SetNumberA(numberA float64) {
divOperation.numberA = numberA
}
func (divOperation *DivOperation) SetNumberB(numberB float64) {
divOperation.numberB = numberB
}
package constant
const (
Add = "+"
Sub = "-"
Mul = "*"
Div = "/"
)
package factory
import "proj/constant"
// ============工厂接口============
type OperationFactory interface {
CreateOperate() Operation
}
// ============加法工厂类============
type AddFactory struct {
}
func (addFactory *AddFactory) CreateOperate() Operation {
return &AddOperation{}
}
// ============减法工厂类============
type SubFactory struct {
}
func (subFactory *SubFactory) CreateOperate() Operation {
return &SubOperation{}
}
// ============乘法工厂类============
type MulFactory struct {
}
func (mulFactory *MulFactory) CreateOperate() Operation {
return &MulOperation{}
}
// ============除法工厂类============
type DivFactory struct {
}
func (divFactory *DivFactory) CreateOperate() Operation {
return &DivOperation{}
}
// 用一个简单工厂封装工厂方法
type OperationFactoryCreate struct {
}
func (operationFactoryCreate *OperationFactoryCreate) NewOperationFactory(operate string) OperationFactory {
switch operate {
case constant.Add:
return &AddFactory{}
case constant.Sub:
return &SubFactory{}
case constant.Mul:
return &MulFactory{}
case constant.Div:
return &DivFactory{}
}
return nil
}
package main
import (
"fmt"
"proj/constant"
)
import . "proj/factory"
// 测试
func main() {
// 全局变量
var numberA float64 = 200
var numberB float64 = 100
var operationFactory OperationFactory
var operation Operation
var result float64
var err error
// ============加法============
operationFactory = &AddFactory{}
operation = operationFactory.CreateOperate()
operation.SetNumberA(numberA)
operation.SetNumberB(numberB)
result, err = operation.Calculate()
if err != nil {
fmt.Println(err)
} else {
fmt.Println("Add Result:", result)
}
// ============减法============
operationFactory = &SubFactory{}
operation = operationFactory.CreateOperate()
operation.SetNumberA(numberA)
operation.SetNumberB(numberB)
result, err = operation.Calculate()
if err != nil {
fmt.Println(err)
} else {
fmt.Println("Sub Result:", result)
}
// ============乘法============
operationFactory = &MulFactory{}
operation = operationFactory.CreateOperate()
operation.SetNumberA(numberA)
operation.SetNumberB(numberB)
result, err = operation.Calculate()
if err != nil {
fmt.Println(err)
} else {
fmt.Println("Mul Result:", result)
}
// ============除法============
operationFactory = &DivFactory{}
operation = operationFactory.CreateOperate()
operation.SetNumberA(numberA)
operation.SetNumberB(numberB)
result, err = operation.Calculate()
if err != nil {
fmt.Println(err)
} else {
fmt.Println("Div Result:", result)
}
fmt.Println("========================")
// 简单工厂封装工厂方法
operationFactoryCreate := OperationFactoryCreate{}
// ============加法============
operationFactory = operationFactoryCreate.NewOperationFactory(constant.Add)
operation = operationFactory.CreateOperate()
operation.SetNumberA(numberA)
operation.SetNumberB(numberB)
result, err = operation.Calculate()
if err != nil {
fmt.Println(err)
} else {
fmt.Println("Add Result:", result)
}
// ============减法============
operationFactory = operationFactoryCreate.NewOperationFactory(constant.Sub)
operation = operationFactory.CreateOperate()
operation.SetNumberA(numberA)
operation.SetNumberB(numberB)
result, err = operation.Calculate()
if err != nil {
fmt.Println(err)
} else {
fmt.Println("Sub Result:", result)
}
// ============乘法============
operationFactory = operationFactoryCreate.NewOperationFactory(constant.Mul)
operation = operationFactory.CreateOperate()
operation.SetNumberA(numberA)
operation.SetNumberB(numberB)
result, err = operation.Calculate()
if err != nil {
fmt.Println(err)
} else {
fmt.Println("Mul Result:", result)
}
// ============除法============
operationFactory = operationFactoryCreate.NewOperationFactory(constant.Div)
operation = operationFactory.CreateOperate()
operation.SetNumberA(numberA)
operation.SetNumberB(numberB)
result, err = operation.Calculate()
if err != nil {
fmt.Println(err)
} else {
fmt.Println("Div Result:", result)
}
}
# 程序输出
Add Result: 300
Sub Result: 100
Mul Result: 20000
Div Result: 2
========================
Add Result: 300
Sub Result: 100
Mul Result: 20000
Div Result: 2
3、Java实现简单计算器
package com.factory;
// 这里实现一个简单的计算器
// 计算接口,包含计算数的设置和结果的计算
public abstract class Operation {
private double numberA;
private double numberB;
// 设置进行计算的两个数
public double getNumberA() {
return numberA;
}
public void setNumberA(double numberA) {
this.numberA = numberA;
}
public double getNumberB() {
return numberB;
}
public void setNumberB(double numberB) {
this.numberB = numberB;
}
// 计算
public abstract double Calculate();
}
package com.factory;
// ============加法===========
public class AddOperation extends Operation {
@Override
public double Calculate() {
return this.getNumberA() + this.getNumberB();
}
}
package com.factory;
// ============减法============
public class SubOperation extends Operation {
@Override
public double Calculate() {
return this.getNumberA() - this.getNumberB();
}
}
package com.factory;
// ============乘法============
public class MulOperation extends Operation {
@Override
public double Calculate() {
return this.getNumberA() * this.getNumberB();
}
}
package com.factory;
// ============除法============
public class DivOperation extends Operation {
@Override
public double Calculate() {
if (this.getNumberB() == 0) {
throw new RuntimeException("被除数不能为0!");
} else {
return this.getNumberA() / this.getNumberB();
}
}
}
package com.factory;
public enum OperationType {
ADD, SUB, MUL, DIV;
}
package com.factory;
// ============工厂接口============
public interface OperationFactory {
Operation CreateOperate();
}
package com.factory;
// ============加法工厂类============
public class AddFactory implements OperationFactory {
@Override
public Operation CreateOperate() {
return new AddOperation();
}
}
package com.factory;
// ============减法工厂类============
public class SubFactory implements OperationFactory {
@Override
public Operation CreateOperate() {
return new SubOperation();
}
}
package com.factory;
// ============乘法工厂类============
public class MulFactory implements OperationFactory{
@Override
public Operation CreateOperate() {
return new MulOperation();
}
}
package com.factory;
// ============除法工厂类============
public class DivFactory implements OperationFactory {
@Override
public Operation CreateOperate() {
return new DivOperation();
}
}
package com.factory;
// 用一个简单工厂封装工厂方法
// ============工厂类============
public class OperationFactoryCreate {
public OperationFactory NewOperationFactory(OperationType operate) {
switch (operate) {
case ADD:
return new AddFactory();
case SUB:
return new SubFactory();
case MUL:
return new MulFactory();
case DIV:
return new DivFactory();
}
return null;
}
}
package com.factory;
public class Test {
public static void main(String[] args) {
// 全局变量
Operation operation = null;
double result = 0;
OperationFactory operationFactory = null;
// ============加法============
operationFactory = new AddFactory();
operation = operationFactory.CreateOperate();
operation.setNumberA(200);
operation.setNumberB(100);
result = operation.Calculate();
System.out.println("result :" + result);
// ============减法============
operationFactory = new SubFactory();
operation = operationFactory.CreateOperate();
operation.setNumberA(200);
operation.setNumberB(100);
result = operation.Calculate();
System.out.println("result :" + result);
// ============乘法============
operationFactory = new MulFactory();
operation = operationFactory.CreateOperate();
operation.setNumberA(200);
operation.setNumberB(100);
result = operation.Calculate();
System.out.println("result :" + result);
// ============除法============
operationFactory = new DivFactory();
operation = operationFactory.CreateOperate();
operation.setNumberA(200);
operation.setNumberB(100);
result = operation.Calculate();
System.out.println("result :" + result);
System.out.println("========================");
// 简单工厂封装工厂方法
OperationFactoryCreate operationFactoryCreate = new OperationFactoryCreate();
// ============加法============
operationFactory = operationFactoryCreate.NewOperationFactory(OperationType.ADD);
operation = operationFactory.CreateOperate();
operation.setNumberA(200);
operation.setNumberB(100);
result = operation.Calculate();
System.out.println("result :" + result);
// ============减法============
operationFactory = operationFactoryCreate.NewOperationFactory(OperationType.SUB);
operation = operationFactory.CreateOperate();
operation.setNumberA(200);
operation.setNumberB(100);
result = operation.Calculate();
System.out.println("result :" + result);
// ============乘法============
operationFactory = operationFactoryCreate.NewOperationFactory(OperationType.MUL);
operation = operationFactory.CreateOperate();
operation.setNumberA(200);
operation.setNumberB(100);
result = operation.Calculate();
System.out.println("result :" + result);
// ============除法============
operationFactory = operationFactoryCreate.NewOperationFactory(OperationType.DIV);
operation = operationFactory.CreateOperate();
operation.setNumberA(200);
operation.setNumberB(100);
result = operation.Calculate();
System.out.println("result :" + result);
}
}
# 程序输出
result :300.0
result :100.0
result :20000.0
result :2.0
========================
result :300.0
result :100.0
result :20000.0
result :2.0