Scala学习整理[第二十七-二十九章 模块化编程和Java]<Programming In Scala>

第二十七章 模块化编程

package SecondWithProgrammingInScala.Chapter27

import SecondWithProgrammingInScala.Chapter27.SimpleDatabase.FoodCategory

/**
* 适用对象的模块化编程
*
* 即对程序合理的分层和组织 ,将功能划分为一个个模块 ,使之易于修改和替换 ,而对其他模块没有影响
* 就像Java中使用接口衔接程序 ,通过替换实现方法修改底层而不影响使用
* 加上Spring的依赖注入 ,可以很好的分离依赖关系
*
* Scala也可以使用Spring ,也提供了自己的备选方案
* abstract class + trait + 组合 ,将底层实现隐藏 ,模块间通过父类/特质进行交互
*/

//需要持久化的实例类
abstract class Food(val name: String) {
override def toString: String = name
}

class Recipe(val name: String, val ingredients: List[Food], val instructions: String) {
override def toString: String = name
}

//额外功能抽象
trait FoodCategories {

case class FoodCategory(name: String, foods: List[Food])

def allCategories: List[FoodCategory]
}

//抽象数据库接口
abstract class Database extends FoodCategories {
def allFoods: List[Food]

def allRecipes: List[Recipe]

def foodNamed(name: String): Option[Food] = allFoods.find(_.name == name)
}

//浏览器抽象
abstract class Browser {
val database: Database

def recipeUsing(food: Food) = database.allRecipes.filter(recipe => recipe.ingredients.contains(food))

def displayCategory(category: database.FoodCategory) = println(category)

}

//实现扩展数据库类型
trait SimpleFoods {

object Apple extends Food("Apple")

object Orange extends Food("Orange")

object Cream extends Food("Cream")

object Sugar extends Food("Sugar")

def allFoods = List(Apple, Orange, Cream, Sugar)
}

trait SimpleRecipes {
this: SimpleFoods =>

object FruitSalad extends Recipe("Fruit Salad", List(Apple, Orange, Cream, Sugar), "Stir it all together")

def allRecipes: List[Recipe] = List(FruitSalad)
}

object SimpleDatabase extends Database with SimpleFoods with SimpleRecipes {

private var categories = List(
FoodCategory("fruit", List(Apple, Orange)),
FoodCategory("misc", List(Cream, Sugar))
)

def allCategories = categories
}

object StudentDatabase extends Database {

object FrozenFood extends Food("FrozenFood")

object HeadItUp extends Recipe("Heat it up", List(FrozenFood), "Microwave the 'food' for 10 minutes")

override def allFoods = List(FrozenFood)

override def allRecipes = List(HeadItUp)

override def allCategories = List(FoodCategory("edible", List(FrozenFood)))
}

//浏览器入口
object SimpleBrower extends Browser {
val database = SimpleDatabase
}

object StudentBrower extends Browser {
val database = StudentDatabase
}

第二十八章 对象相等

第二十九章 Scala和Java

Scala和Java同为JVM上的语言 ,经过编译器(翻译器)产生.class文件有着许多的相似之处 .scala的一些方法和类也是直接对应到了Java ,也可以直接在代码中调用Java的东西 .但是反过来 ,Java调用Scala则没有那么理想 ,你必须要了解scala编译后的.class结构 ,并通过Java与之产生联系 .