http://scala-programming-language.1934581.n4.nabble.com/java-lang-Class-isArray-performance-hit-td3043990.html#a3043990

ArrayTest.scala

object ArrayTest {
    def time(thunkName: String, iter: Int, thunk: => Boolean) = {
        // warm up...
        for(i <- 1 to iter) thunk
        // timed...
        val start = System.currentTimeMillis()
        for(i <- 1 to iter) thunk
        val timing = System.currentTimeMillis() - start
        println(String.format("Ran %d iterations of [%s] in %d ms.", iter.asInstanceOf[AnyRef], thunkName, timing.asInstanceOf[AnyRef]))
    }

    def main(args: Array[String]) = {
        val array = Array("An", "array", "of", "test", "string")
        def isArrayTest = array.getClass.isArray
        def charAtTest = array.getClass.getName.charAt(0) == '['
        val iter = 100000000;
        time("isArrayTest", iter, isArrayTest)
        time("charAtTest", iter, charAtTest)
    }
}