scala 叠加在一起的特质 举例

1、编写Logged.scala：

trait Logged{
def log(msg:String){}
}
class BankAccount(initialBalance:Double){
//var balance=initialBalance
private var balance=initialBalance
def deposit(amount:Double)={balance+=amount;balance}
def withdraw(amount:Double)={balance-=amount;balance}
def query()=balance
}
class SavingsAccount(initialBalance:Double) extends BankAccount(initialBalance){
private var num:Int=_
def earnMonthlyInterest()={//每月执行一次
num=3 //每月有三次免手续费（1元）
super.deposit(1) //月利息1元
}
override def deposit(amount:Double)={
if(num>0){num-=1;super.deposit(amount)}
else super.deposit(amount-1)
}
override def withdraw(amount:Double)={
if(num>0){num-=1;super.withdraw(amount)}
else super.withdraw(amount+1)
}
}
class SavingsAccount2(initialBalance:Double) extends SavingsAccount(initialBalance) with Logged{
override def withdraw(amount:Double)={
//if(amount>balance){log("Insufficient funds");-1} //withdraw返回一个Double型值，操作失败时，返回-1。
//这里可以找到balance，是因为，基类里是没有private属性。但是这样做是不安全的。
if(amount>query){log("Insufficient funds");-1} //withdraw返回一个Double型值，操作失败时，返回-1。
else {log("withdraw success");super.withdraw(amount)}
}
}
trait ConsoleLogger extends Logged{
override def log(msg:String){println(msg)}
}
trait TimestampLogger extends Logged{
override def log(msg:String){
super.log(new java.util.Date()+" "+msg)
}
}
trait ShortLogger extends Logged{
val maxLength=15
override def log(msg:String){
super.log(
if(msg.length<=maxLength) msg
else msg.substring(0,maxLength-3)+"..."
)
}
}2、编译：scalac Logged.scala
3、在scala的REPL里：

scala> val test=new SavingsAccount2(100) with ConsoleLogger with TimestampLogger

test: SavingsAccount2 with ConsoleLogger with TimestampLogger = $anon$1@1b75756

scala> test.withdraw(10)
Sun Jul 03 14:00:51 CST 2016 withdraw success
res18: Double = 89.0

scala> val test2=new SavingsAccount2(100) with ConsoleLogger with TimestampLogge
r with ShortLogger
test2: SavingsAccount2 with ConsoleLogger with TimestampLogger with ShortLogger
= $anon$1@9b0a6f

scala> test2.withdraw(10)
Sun Jul 03 14:01:59 CST 2016 withdraw suc...
res19: Double = 89.0

scala> val test3=new SavingsAccount2(100) with ConsoleLogger with ShortLogger wi
th TimestampLogger
test3: SavingsAccount2 with ConsoleLogger with ShortLogger with TimestampLogger
= $anon$1@81065e

scala> test3.withdraw(10)
Sun Jul 03 1...
res20: Double = 89.0