Scala number, date, and formatting examples

This blog post contains a collection of Scala number and date examples. I created most of these in the process of writing the Scala Cookbook. Unlike the Cookbook, I don’t describe the examples here much at all, I just show the examples, mostly as a reference for myself (and anyone else that can benefit from them).

 

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Scala numeric types

Scala has these numeric types:

Byte
Char
Double
Float
Int
Long
Short

Their maximum values are shown here:

Byte.MaxValue     // Byte = 127
Char.MaxValue     // (output omitted)
Double.MaxValue   // Double = 1.7976931348623157E308
Float.MaxValue    // Float = 3.4028235E38
Int.MaxValue      // Int = 2147483647
Long.MaxValue     // Long = 9223372036854775807
Short.MaxValue    // Short = 32767
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Numeric conversions

You can convert string to each of the numeric types:

"1".toByte       // Byte = 1
"100".toDouble   // Double = 100.0
"100".toFloat    // Float = 100.0
"100".toInt      // Int = 100
"1".toLong       // Long = 1
"1".toShort      // Short = 1

// exceptions
"foo".toInt      // java.lang.NumberFormatException: For input string: "foo"
"19.45".toInt    // java.lang.NumberFormatException: For input string: "19.45"

More data conversions:

19.toByte       // Byte = 19
19.toDouble     // Double = 19.0
19.toFloat      // Float = 19.0
19.45.toInt     // Int = 19
19.toLong       // Long = 19
19.toShort      // Short = 19
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Setting numeric values implicitly and explicitly

Scala normally determines data types implicitly, but you can also set them explicitly:

// implicit
val a = 0          // Int = 0
val b = 1.0        // Double = 1.0

// explicit
val a: Byte = 0    // Byte = 0
val a: Double = 0  // Double = 0.0
val a: Float = 0   // Float = 0.0
val a: Int = 0     // Int = 0
val a: Long = 0    // Long = 0
val a: Short = 0   // Short = 0

// this works
val a = 1d         // Double = 1.0
val a = 1f         // Float = 1.0

// octal (preceding '0')
val a = 040        // Int = 32

// hex (leading 0x or 0X)
val a = 0x20       // Int = 32

// hex to Long
val a = 0x20L      // Long = 32

There is no ++ and --:

// use += and -=
var a = 1
a += 1      // 2
a -= 1      // 1

// multiplication and division
a *= 2      // 2
a *= 2      // 4
a /= 2      // 2
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Scala BigInt and BigDecimal

Scala includes BigInt and BigDecimal support:

var b = BigInt(1234567890)       // scala.math.BigInt = 1234567890
var b = BigDecimal(123456.789)   // scala.math.BigDecimal = 123456.789

// support numeric operators
b+b              // scala.math.BigInt = 2469135780
b*b              // scala.math.BigInt = 1524157875019052100
b += 1           // 1234567891

// convert to other numeric types
b.toInt          // Int = 1234567891
b.toLong         // Long = 1234567891
b.toFloat        // Float = 1.23456794E9
b.toDouble       // Double = 1.234567891E9

// test them
b.isValidByte    // Boolean = false
b.isValidChar    // Boolean = false
b.isValidInt     // Boolean = true
b.isValidShort   // Boolean = false
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Random numbers

You can do all the usual random number things:

var r = scala.util.Random
r.nextInt         // Int = -1323477914
r.nextInt(100)    // Int = 58

// between 0.0 and 1.0, no args req'd
r.nextFloat       // Float = 0.50317204

// between 0.0 and 1.0, no args req'd
r.nextDouble      // Double = 0.6946000981900997

// seed
r.setSeed(1945)

// random characters
r.nextPrintableChar    // Char = H
r.nextPrintableChar    // Char = r
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Number formatting

There are a wide variety of ways to format numeric output:

"%1.5f".format(pi)                   // String = 3.14159
"%1.3f".format(pi)                   // String = 3.142

// zero-filled
"%06.2f".format(scala.math.Pi)       // String = 003.14

// currency
"$%.2f".format(123.456789)           // String = $123.46
"$%.2f".format(1234.56789)           // String = $1234.57
"$%.2f".format(12345.6789)           // String = $12345.68

val format = java.text.NumberFormat.getCurrencyInstance
println(format.format(123.456789))   // $123.46
println(format.format(1234.56789))   // $1,234.57
println(format.format(12345.6789))   // $12,345.68
println(format.format(123456.789))   // $123,456.79

// locale
import java.util.Locale
import java.util.Currency
val de = Currency.getInstance(new Locale("de", "DE"))
format.setCurrency(de)
println(format.format(123456.789))   // EUR123,456.79

You’ll find math functions under scala.math:

import scala.math._
sqrt(4)           // Double = 2.0
pow(2,1)          // Double = 2.0
abs(-1)           // Int = 1
pow(2,2)          // Double = 4.0
pow(2,3)          // Double = 8.0
round(19.49)      // Long = 19
ceil(19.1)        // Double = 20.0
floor(19.1)       // Double = 19.0

// Pi and E
scala.math.Pi     // Double = 3.141592653589793
scala.math.E      // Double = 2.718281828459045
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Scala date and time examples

You can use Java classes for date and time handling:

import java.text.SimpleDateFormat
import java.util.Calendar

val today = Calendar.getInstance.getTime
     
// create the date/time formatters
val minuteFormat = new SimpleDateFormat("mm")
val hourFormat = new SimpleDateFormat("hh")
val amPmFormat = new SimpleDateFormat("a")
 
val currentHour = hourFormat.format(today)      // 12
val currentMinute = minuteFormat.format(today)  // 29
val amOrPm = amPmFormat.format(today)           // PM

You can also use the nscala-time library and Joda time:

import com.github.nscala_time.time.Imports._
import org.joda.time.Days
 
// from <a href="http://alvinalexander.com" title="http://alvinalexander.com">http://alvinalexander.com</a>
object DaysUntilChristmas extends App {
 
    // 1: get the current date and time
    val now = DateTime.now
   
    // 2: get a date to represent Christmas
    val xmas = (new DateTime).withYear(2013)
                            .withMonthOfYear(12)
                            .withDayOfMonth(25)
   
    // 3: determine the number of days from now until xmas
    val daysToXmas = Days.daysBetween(now, xmas).getDays
   
    // 4: print the result
    println(s"daysToXmas = $daysToXmas")
 
    // bonus: what day is 200 days from now?
    val nowPlus200 = now + 200.days
    println(s"nowPlus200 = $nowPlus200")
 
}
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Summary

In summary, I hope these Scala number/numeric examples have been helpful. I’ll keep updating this blog post as I come up with more examples.

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