Objects: Singletons, Part 2

A second way to use objects in Scala is to put a collection of related functions inside the object. I refer to this as a utility object, although I don't know if there's any formal name in standard for this approach. Several examples of this approach are:

StringUtils
FileUtils
NetworkUtils

If you’re familiar with Java, the end result is similar to using static members in Java classes.

Example:

object StringUtils:

    // return true if the string is null or empty
    def isNullOrEmpty(s: String): Boolean = 
        if s==null || s.trim.equals("") then true else false

    // convert "big belly burger" to "Big Belly Burger"
    def capitalizeAllWords(s: String): String = 
        s.split(" ")
         .map(_.capitalize)
         .mkString(" ")

Usage examples:

StringUtils.isNullOrEmpty("")
    // result: true

StringUtils.capitalizeAllWords("big belly burger")
    // result: Big Belly Burger

Importing members from an object

When you were using methods from a utility object like this, another approach is to import them as shown in this example, and then you can just use the function names directly:

import StringUtils.*

isNullOrEmpty("")
capitalizeAllWords("big belly burger")

If you keep building on this concept, you can create collections of utility classes for all sorts of things:

object StringUtils:
    def isNullOrEmpty(s: String): Boolean = ???
    def capitalizeAllWords(s: String): String = ???

object FileUtils:
    def readFile(filename: String): Try[Seq[String]] = ???
    def writeFile(filename: String, contents: String): Try[Boolean] = ???

object NetworkUtils:
    def getUrlContent(url: String): String = ???

object StockUtils:
    def buildUrl(stockSymbol: String): String = ???
    def getPrice(stockSymbol: String, html: String): String = ???
    def getVolume(stockSymbol: String, html: String): String = ???
    def getHigh(stockSymbol: String, html: String): String = ???
    def getLow(stockSymbol: String, html: String): String = ???

object DateUtils:
    def currentDate: String = ???
    def currentTime: String = ???

Importing members from an object

books by alvin