Listing 10.6 should be

class LineElement(s: String) extends ArrayElement(Array(s)) {
  override val width = s.length
  override val height = 1
}

It uses def instead of val which gives the following compiler error:

LineElement.scala:2: error: overriding value width in class Element of
type Int;
 method width needs to be a stable, immutable value
  override def width = s.length
               ^
LineElement.scala:3: error: overriding value height in class Element of
type Int;
 method height needs to be a stable, immutable value
  override def height = 1

In the implementation of the class `UniformElement',
  private val line = ch.toString * width
should really be
  private def line = ch.toString * width

Otherwise, the code can compile, but will throw a
 java.lang.ExceptionInInitializerError
 Caused by: java.lang.NullPointerException

Tested at Debian Squeeze, with Scala version 2.7.7final

class UniformElement(
ch: Char,
override val width: Int,
override val height: Int
) extends Element {
private val line = ch.toString * width
def contents = Array.make(height, line)
}

Array does not have a make method (scala 2.10.0-RC2. I'm using ItelliJ
and this is syntax highlighted as unknown and I can't find it in the
documentation

2nd, 3rd line: Replace "We'll override demo in in ArrayElement..." by
"We'll override demo in ArrayElement...".

FIXED

class UniformElement(
ch: Char,
override val width: Int,
override val height: Int
) extends Element {
private val line = ch.toString * width
def contents = Array.make(height, line)
}

Array.make(height, line) can be replaced with
Array.fill(height)(Line)