Golang学习数据结构和算法中文版第6篇

　　《Learn Data Structures and Algorithms with Golang》作者: Bhagvan Kommadi
　　享元(Flyweight)
　　享元用来管理一个带有高度变化对象的状态。这个模式允许我们多个对象之间共享对象状态的公共部分，而不是共享存储它的每个对象。变化的对象数据看做外部状态，而对象状态的其余部分是内部状态。外部数据被传给享元方法且不会被存储在对象里。享元模式有助于减少整体内存使用和对象初始化开销。此模式有助于创建类之间关系和降低内存到可管理水平。
　　享元对象是不可变的。值对象是一个享元模式的好例子。享元对象可以创建在单独线程模式里，确保每个值一个实例。在并发线程场景里会创建很多实例。这是基于享元对象的平等标准。
　　享元模式的参与者是FlyWeight接口，ConcreteFlyWeight类，FlyWeightFactory类型和Client类：FlyWeight接口有一个方法，通过此方法flyweights可以得到外部状态和对它起作用。ConcreteFlyWeight实现FlyWeight接口来表示享元对象。FlyWeightFactory类用来创建和管理享元对象。客户端调用FlyWeightFactory得到一个享元对象。UnsharedFlyWeight有一个禁用共享功能。Client类
　　让我们假设DataTransferObject是带有getId方法的接口。DataTransferObjectFactory创建一个数据传输对象通过带DTO类型参数的getDataTransferObject方法。DTO类型包括客户，员工，管理者和地址，如下代码所示：//main package has examples shown // in Hands-On Data Structures and algorithms with Go book package main // importing fmt package import (   ＂fmt＂ ) //DataTransferObjectFactory struct type DataTransferObjectFactory struct {   pool map[string] DataTransferObject } //DataTransferObjectFactory class method getDataTransferObject func (factory DataTransferObjectFactory) getDataTransferObject(dtoType string) DataTransferObject {   var dto = factory.pool[dtoType]   if dto == nil {     fmt.Println(＂new DTO of dtoType: ＂ + dtoType)     switch dtoType{       case ＂customer＂:         factory.pool[dtoType] = Customer{id:＂1＂}       case ＂employee＂:         factory.pool[dtoType] = Employee{id:＂2＂}       case ＂manager＂:         factory.pool[dtoType] = Manager{id:＂3＂}       case ＂address＂:         factory.pool[dtoType] = Address{id:＂4＂}     }     dto = factory.pool[dtoType]   }   return dto }
　　在下面代码里，DataTransferObject接口由Customer类实现：// DataTransferObject interface type DataTransferObject interface {   getId() string } //Customer struct type Customer struct {   id string //sequence generator   name string   ssn string } // Customer class method getId func (customer Customer) getId() string {   //fmt.Println(＂getting customer Id＂)   return customer.id } //Employee struct type Employee struct {   id string   name string } //Employee class method getId func (employee Employee) getId() string {   return employee.id } //Manager struct type Manager struct {   id string   name string   dept string }
　　DataTransferObject接口由Manager类实现，代码如下：//Manager class method getId func (manager Manager) getId() string {   return manager.id } //Address struct type Address struct {   id string   streetLine1 string   streetLine2 string   state string   city string } //Address class method getId func (address Address) getId() string{   return address.id } //main method func main() {   var factory = DataTransferObjectFactory{make(map[string]DataTransferObject)}   var customer DataTransferObject = factory.getDataTransferObject(＂customer＂)   fmt.Println(＂Customer ＂,customer.getId())   var employee DataTransferObject = factory.getDataTransferObject(＂employee＂)   fmt.Println(＂Employee ＂,employee.getId())   var manager DataTransferObject = factory.getDataTransferObject(＂manager＂)   fmt.Println(＂Manager＂,manager.getId())   var address DataTransferObject = factory.getDataTransferObject(＂address＂)   fmt.Println(＂Address＂,address.getId()) }
　　运行下面的命令：go run flyweight.go
　　让我们在下一节看看私有类和代理数据模式。
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