1、Trait基础设计模式
一、将trait做为接口使用ide
// Scala中的Triat是一种特殊的概念
// 首先咱们能够将Trait做为接口来使用,此时的Triat就与Java中的接口很是相似
// 在triat中能够定义抽象方法,就与抽象类中的抽象方法同样,只要不给出方法的具体实现便可
// 类可使用extends关键字继承trait,注意,这里不是implement,而是extends,在scala中没有implement的概念,不管继承类仍是trait,统一都是extends
// 类继承trait后,必须实现其中的抽象方法,实现时不须要使用override关键字
// scala不支持对类进行多继承,可是支持多重继承trait,使用with关键字便可
###
scala> :paste
// Entering paste mode (ctrl-D to finish)
trait SayHello {
def sayHello(name: String)
}
trait MakeFriends {
def makeFriends(p: Person)
}
class Person(val name: String) extends SayHello with MakeFriends {
def sayHello(otherName: String) = println("Hello, " + otherName + ", I'm " + name)
def makeFriends(p: Person) = println("Hello " + p.name + ", I'm " + name + ", I want to make friends with you.")
}
// Exiting paste mode, now interpreting.
defined trait SayHello
defined trait MakeFriends
defined class Person
scala> val p = new Person("leo")
p: Person = Person@223f3642
scala> val p2 = new Person("jack")
p2: Person = Person@48fa0f47
scala> p.sayHello("jack")
Hello, jack, I'm leo
scala> p.makeFriends(p2)
Hello jack, I'm leo, I want to make friends with you.
二、在Trait中定义具体方法函数
// Scala中的Triat能够不是只定义抽象方法,还能够定义具体方法,此时trait更像是包含了通用工具方法的东西// 有一个专有的名词来形容这种状况,
就是说trait的功能混入了类
// 举例来讲,trait中能够包含一些不少类都通用的功能方法,好比打印日志等等,spark中就使用了trait来定义了通用的日志打印方法
###
scala> :paste
// Entering paste mode (ctrl-D to finish)
trait Logger {
def log(msg: String) = println("log: " + msg)
}
class Person(val name: String) extends Logger {
def sayHello {
println("Hello, I'm " + name); log("sayHello is invoked")
}
}
// Exiting paste mode, now interpreting.
defined trait Logger
defined class Person
scala> val p = new Person("leo")
p: Person = Person@2898ac89
scala> p.sayHello
Hello, I'm leo
log: sayHello is invoked
三、在Trait中定义具体字段工具
// Scala中的Triat能够定义具体field,此时继承trait的类就自动得到了trait中定义的field
// 可是这种获取field的方式与继承class是不一样的:若是是继承class获取的field,实际是定义在父类中的;而继承trait获取的field,就直接被添加到了类中
###
scala> :paste
// Entering paste mode (ctrl-D to finish)
trait Person {
val eyeNum: Int = 2
}
class Student(val name: String) extends Person {
def sayHello = println("Hi, I'm " + name + ", I have " + eyeNum + "eyes.")
}
// Exiting paste mode, now interpreting.
defined trait Person
defined class Student
scala> val s = new Student("leo")
s: Student = Student@4b0d79fc
scala> s.sayHello
Hi, I'm leo, I have 2eyes.
四、在Trait中定义抽象字段spa
// Scala中的Triat能够定义抽象field,而trait中的具体方法则能够基于抽象field来编写
// 可是继承trait的类,则必须覆盖抽象field,提供具体的值
###
scala> :paste
// Entering paste mode (ctrl-D to finish)
trait SayHello {
val msg: String
def sayHello(name: String) = println(msg + ", " + name)
}
class Person(val name: String) extends SayHello {
val msg: String = "hello"
def makeFriends(p: Person) {
sayHello(p.name)
println("I;m " + name + ", I want to make friend with you.")
}
}
// Exiting paste mode, now interpreting.
defined trait SayHello
defined class Person
scala> val p1 = new Person("leo")
p1: Person = Person@62656be4
scala> val p2 = new Person("jack")
p2: Person = Person@56dc1551
scala> p1.makeFriends(p2)
hello, jack
I;m leo, I want to make friend with you.
2、trait高级scala
一、为实例混入trait设计
// 有时咱们能够在建立类的对象时,指定该对象混入某个trait,这样,就只有这个对象混入该trait的方法,而类的其余对象则没有
###
scala> :paste
// Entering paste mode (ctrl-D to finish)
trait Logged {
def log(msg: String) {}
}
trait MyLogger extends Logged {
override def log(msg: String) {println("log: " + msg)}
}
class Person(val name: String) extends Logged {
def sayHello {println("Hi, I'm " + name); log("sayHello is invoked!")}
}
// Exiting paste mode, now interpreting.
defined trait Logged
defined trait MyLogger
defined class Person
scala> val p1 = new Person("leo")
p1: Person = Person@35d08e6c
scala> p1.sayHello
Hi, I'm leo
scala> val p2 = new Person("jack") with MyLogger
p2: Person with MyLogger = $anon$1@1bb564e2
scala> p2.sayHello
Hi, I'm jack
log: sayHello is invoked!
二、trait调用链日志
// Scala中支持让类继承多个trait后,依次调用多个trait中的同一个方法,只要让多个trait的同一个方法中,在最后都执行super.方法便可
// 类中调用多个trait中都有的这个方法时,首先会从最右边的trait的方法开始执行,而后依次往左执行,造成一个调用链条
// 这种特性很是强大,其实就至关于设计模式中的责任链模式的一种具体实现
###
scala> :paste
// Entering paste mode (ctrl-D to finish)
trait Handler {
def handle(data: String) {}
}
trait DataVailHandler extends Handler {
override def handle(data: String) {
println("check data: " + data)
super.handle(data)
}
}
trait SignatureVaildHandler extends Handler {
override def handle(data: String) {
println("check signature: " + data)
}
}
class Person(val name: String) extends SignatureVaildHandler with DataVailHandler {
def sayHello = {println("Hello," + name); handle(name)}
}
// Exiting paste mode, now interpreting.
defined trait Handler
defined trait DataVailHandler
defined trait SignatureVaildHandler
defined class Person
scala> val p = new Person("leo")
p: Person = Person@545de5a4
scala> p.sayHello
Hello,leo
check data: leo
check signature: leo
三、在trait中覆盖抽象方法code
// 在trait中,是能够覆盖父trait的抽象方法的
// 可是覆盖时,若是使用了super.方法的代码,则没法经过编译。由于super.方法就会去掉用父trait的抽象方法,此时子trait的该方法仍是会被认为是抽象的
// 此时若是要经过编译,就得给子trait的方法加上abstract override修饰
###
scala> :paste
// Entering paste mode (ctrl-D to finish)
trait Logger {
def log(msg: String)
}
trait Mylogger extends Logger {
abstract override def log(msg: String) {super.log(msg)}
}
// Exiting paste mode, now interpreting.
defined trait Logger
defined trait Mylogger
四、混合使用trait的具体方法和抽象方法对象
// 在trait中,能够混合使用具体方法和抽象方法
// 可让具体方法依赖于抽象方法,而抽象方法则放到继承trait的类中去实现
// 这种trait其实就是设计模式中的模板设计模式的体现
###
scala> :paste
// Entering paste mode (ctrl-D to finish)
trait Valid {
def getName: String
def valid: Boolean = {
getName == "leo"
}
}
class Person(val name: String) extends Valid {
println(valid)
def getName = name
}
// Exiting paste mode, now interpreting.
defined trait Valid
defined class Person
scala> val p = new Person("leo")
true
p: Person = Person@3f093abe
五、trait的构造机制
// 在Scala中,trait也是有构造代码的,也就是trait中的,不包含在任何方法中的代码
// 而继承了trait的类的构造机制以下:一、父类的构造函数执行;二、trait的构造代码执行,多个trait从左到右依次执行;
三、构造trait时会先构造父trait,若是多个trait继承同一个父trait,则父trait只会构造一次;四、全部trait构造完毕以后,子类的构造函数执行
###
scala> :paste
// Entering paste mode (ctrl-D to finish)
class Person {
println("Persons's constructor!")
}
trait Logger {
println("Logger's constructor!")
}
trait MyLogger extends Logger {
println("MyLogger's constructor!")
}
trait TimeLogger extends Logger {
println("TimeLogger's constructor!")
}
class Student extends Person with MyLogger with TimeLogger {
println("Student's constructor!")
}
// Exiting paste mode, now interpreting.
defined class Person
defined trait Logger
defined trait MyLogger
defined trait TimeLogger
defined class Student
scala> val s = new Student
Persons's constructor!
Logger's constructor!
MyLogger's constructor!
TimeLogger's constructor!
Student's constructor!
s: Student = Student@158d255c
六、trait field的初始化
// 在Scala中,trait是没有接收参数的构造函数的,这是trait与class的惟一区别,可是若是需求就是要trait可以对field进行初始化,该怎么办呢?
只能使用Scala中很是特殊的一种高级特性 - 提早定义
###
scala> trait sayHello {
| val msg: String
| println(msg.toString)
| }
defined trait sayHello
scala> class Person
defined class Person
scala> val p = new {
| val msg: String = "init"
| } with Person with sayHello
init
p: Person with sayHello = $anon$1@1af7f54a
七、trait继承class
// 在Scala中,trait也能够继承自class,此时这个class就会成为全部继承该trait的类的父类
###
scala> :paste
// Entering paste mode (ctrl-D to finish)
class MyUtil {
def printMessage(msg: String) = println(msg)
}
trait Logger extends MyUtil {
def log(msg: String) = printMessage("log: " + msg)
}
class Person(val name: String) extends Logger {
def sayHello {
log("Hi, I'm " + name)
printMessage("Hi, I'm" + name)
}
}
// Exiting paste mode, now interpreting.
defined class MyUtil
defined trait Logger
defined class Person
scala> val p = new Person("leo")
p: Person = Person@6650813a
scala> p.sayHello
log: Hi, I'm leo
Hi, I'mleo