Scala类型边界和Java通用互操作

我正在尝试包装rxjava的timeout 方法,以使其可用于scala.

与我尝试过的许多其他方法类似:

def timeout[U >: T](timeout: Duration, other: Observable[U]): Observable[U] = {
  val otherJava: rx.Observable[_ <: U] = other.asJavaObservable
  val thisJava:  rx.Observable[_ <: U] = this.asJavaObservable
  toScalaObservable[U](thisJava.timeout(timeout.length, timeout.unit, otherJava))
}

但是我收到以下错误:

Observable.scala:1631: error: overloaded method value timeout with alternatives:
($1: Long,x$2: java.util.concurrent.TimeUnit,x$3: rx.Scheduler)rx.Observable[_$85] 
($1: Long,x$2: java.util.concurrent.TimeUnit,x$3: rx.Observable[_ <: _$85])rx.Observable[_$85]
cannot be applied to (Long, scala.concurrent.duration.TimeUnit, rx.Observable[_$84])
  toScalaObservable[U](thisJava.timeout(timeout.length, timeout.unit, otherJava))

原始的java方法:

public Observable timeout(long timeout, TimeUnit timeUnit, Observable other) {
   return create(OperationTimeout.timeout(this, timeout, timeUnit, other));
}

我不是很熟悉,没有Java和斯卡拉(和所有类型的边界),但据我的理解:无论otherJava以及thisJava类型为rx.Observable[U],那么他们为什么不排队？