一.为类提供可以堆叠的改变
package com.jason.qianfeng
trait Loggertest {
def logger(msg: String)
}
trait ConsoleLogger extends Loggertest {
override def logger(msg: String): Unit = println(msg)
}
trait TimestampLogger extends ConsoleLogger {
override def logger(msg: String): Unit = super.logger(s"${java.time.Instant.now()} : $msg")
}
trait ShortterLogger extends ConsoleLogger {
override def logger(msg: String): Unit = {
val msgLenghth = 16
if (msg.length > msgLenghth) {
super.logger(msg.take(13) + "...")
} else {
super.logger(msg)
}
}
}
abstract class Account {
protected var balance = 0.0
}
class Saving extends Account with ConsoleLogger {
def withdraw(ammount: Double): Unit = {
if (ammount > balance) logger(s"balance is not enough")
else balance -= ammount
}
}
object TraitTest2 {
def main(args: Array[String]): Unit = {
val acc1 = new Saving with TimestampLogger with ShortterLogger
val acc2 = new Saving with ShortterLogger with TimestampLogger
val acc3 = new Saving with ShortterLogger
val acc4 = new Saving with TimestampLogger
val acc5 = new Saving
acc1.withdraw(100.0)
acc2.withdraw(100.0)
acc3.withdraw(100.0)
acc4.withdraw(100.0)
acc5.withdraw(100.0)
}
}输出结果
2018-08-25T13:14:53.644Z : balance is no... // 先截断msg 再 加上timestamp
2018-08-25T13... //先给msg加上timestamp 再 截断
balance is no...
2018-08-25T13:14:53.814Z : balance is not enough
balance is not enough
1.创建Saving 实例时所混入的特质必须是ConsoleLogger的子类，否则会报错
2.程序执行时按照从右到左的顺序调用特质的方法
二.特质当做父接口使用
package com.jason.qianfeng
trait Logger3 {
def log(msg: String)
def info(msg: String) = log(s"INFO : $msg")
def warn(msg: String) = log(s"WARN : ${msg}")
def severe(msg: String) = log(s"SEVERE : $msg")
}
class Accout3 {
protected var balance = 0.0
}
class Saving3 extends Accout3 with Logger3 {
override def log(msg: String): Unit = println(msg)
def withDraw(ammount: Double) = {
if (ammount > balance) {
severe("insufficient funds")
} else {
balance -= ammount
info(s"withdraw funds ${ammount}")
}
}
}
object TraitTest3 {
def main(args: Array[String]): Unit = {
val sav = new Saving3()
sav.withDraw(100)
}
}在Logger3中定义了抽象方法log，Saving3中对log方法进行了实现，并且可以调用Logger3 的 其他方法