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2.9. Formatting Numbers and Currency
Problem
You want to format numbers or currency to control decimal places and commas, typically for printed output.
Solution
For basic number formatting, use the f string interpolator shown in Recipe 1.4:
scala> val pi = scala.math.Pipi: Double = 3.141592653589793

scala> println(f"$pi%1.5f")3.14159

A few more examples demonstrate the technique:
scala> f"$pi%1.5f"res0: String = 3.14159

scala> f"$pi%1.2f"res1: String = 3.14

scala> f"$pi%06.2f"res2: String = 003.14

If you’re using a version of Scala prior to 2.10, or prefer the explicit use of the formatmethod, you can write the code like this instead:
scala> "%06.2f".format(pi)res3: String = 003.14

A simple way to add commas is to use the getIntegerInstance method of thejava.text.NumberFormat class:
scala> val formatter = java.text.NumberFormat.getIntegerInstanceformatter: java.text.NumberFormat = java.text.DecimalFormat@674dc

scala> formatter.format(10000)res0: String = 10,000

scala> formatter.format(1000000)res1: String = 1,000,000

You can also set a locale with the getIntegerInstance method:
scala> val locale = new java.util.Locale("de", "DE")locale: java.util.Locale = de_DE

scala> val formatter = java.text.NumberFormat.getIntegerInstance(locale)formatter: java.text.NumberFormat = java.text.DecimalFormat@674dc

scala> formatter.format(1000000)res2: String = 1.000.000

You can handle floating-point values with a formatter returned by getInstance:
scala> val formatter = java.text.NumberFormat.getInstance ...