println vs System.out.println in Scala

I always thought that Predef.println was merely a shortcut for System.out.println, but apparently I am mistaken, since it doesn't seem to use System.out at all. Why is that so? And how can I do the "redirecting" of System.out be开发者_StackOverflow中文版low in Scala?

scala> val baos = new java.io.ByteArrayOutputStream
baos: java.io.ByteArrayOutputStream = 

scala> val ps = new java.io.PrintStream(baos)
ps: java.io.PrintStream = java.io.PrintStream@6c5ac4

scala> System.setOut(ps)

scala> println("hello")
hello

scala> new String(baos.toByteArray)
res2: java.lang.String = ""

scala> System.out.println("hello")

scala> new String(baos.toByteArray)
res7: java.lang.String = 
"hello
"

Predef.println is shortcut for Console.println and you can use Console.setOut or Console.withOut for redirecting.

Also, Console.setOut only affects the current thread while System.setOut affects the whole JVM. Additionally Scala 2.9 repl evaluates each line in its own thread, so Console.setOut is not usable there.

scala> val baos = new java.io.ByteArrayOutputStream
baos: java.io.ByteArrayOutputStream = 

scala> Console.withOut(baos)(print("hello"))

scala> println(baos)
hello