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Scala Programming Language
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- intro
- hello world
- arithmetics
- functions
- strings
- array
- list
- set
- map
- tuple
- option
- iterator
- classes
- matching
- exceptions
- misc

-

-

Intro ------------------------------

Scala programs run on JVM (Java Virtual Machine),
but Scala syntax is much simpler than that of Java, and it is very consice - similar to Python.
Scala is object-oriented. Scala is functional. Statically typed. Runs on JVM and can execute Java code, but in Scala:

  • All types are objects.
  • Type inference.
  • Nested Functions.
  • Functions are objects.
  • Domain specific language (DSL) support.
  • Traits.
  • Closures.
  • Concurrency support inspired by Erlang.

Martin Odersky
Martin Odersky, creator of Scala

It was successfully used to develop Apache Spark - architecture for fast distributed data processing.


Hello, world ------------------------------

object MyApp extends App {
  var a = 0;
  for( a <- 1 to 10){  /* comment */
    println( "Value of a: " + a ); // comment
  }
}

Now you can compile and run:
scalac test.scala
scala MyApp

Note in the above example:

If you run scala without file name - it enters interactive mode:

> scala
Welcome to Scala version 2.11.0 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_65).
Type in expressions to have them evaluated.
Type :help for more information.
       
scala> var a=1
a: Int = 1
scala> for(a <- 1 to 3) println("help" + a)
help1
help2
help3
scala> :quit
--
In interactive mode scala has many convenient commands which start with ":", for example:
  :help [command]          print this summary or command-specific help  
  :history [num]           show the history (optional num is commands to show)
  :load <path>             interpret lines in a file
  :paste [-raw] [path]     enter paste mode or paste a file
  :power                   enable power user mode
  :quit                    exit the interpreter
  :save <path>             save replayable session to a file
  :sh <command line>       run a shell command (result is implicitly => List[String])
etc.
etc. - use :help to see the whole list

Note: In interactive mode you can use auto-expansion help by hitting <TAB> key
--
// Two ways to run a scala script in file test.scala: 
// file test.scala:
var word = "World"
println("Hello " + word)

// running from unix prompt:
> scala test.scala

// running from scala prompt
scala>:load test.scala

Similarly you can run scala from spark prompt.

You can also use an IDE with scala plugin, for example:

arithmetics ------------------------------

arithmetics

scala> print(1);print(2)
12
scala> println(1);println(2)
1
2

var ii=5 // type not specified, it will be inferredto be Int
var ii=5L // type will be inferred to be Long
var ff=1.0*ii // 5F , 5D (make it Float or Double explicitly, Double is the default) var ii2 = ff.toInt // toByte, toChar, toDouble, toFloat, toInt, toLong, toShort, toString // declaring a constant using "val":
val aa = 5 // aa is immutable constant, can not be changed (val = 'constant')

// declaring several variables at once:
var (a1: Int, a2: String, a3: Int) = Tuple3(40, "Foo", 50)
--
// removing decimals

ff = 5.9
ii = ff.toInt  // 5
ff = -5.9
ii = ff.toInt  // -5

// rounding

ff = 5.9
ii = ff.round        // 6, Long
ii = ff.round.toInt  // 6, Int 

// round, ceil, floor

// rounding to cents

ff = 12.34567
var ff2 = ((ff*100.0).round)/100.0  // 12.35
ff2 = ((ff*100.0).round)/100.0  // 12.35
      
--
// provide type while declaring the variable:
var ss : String = "ABCDE"

// string to number var ss = " 55.01 " ff = ss.toFloat // 55.0099983215332 ii = ss.toFloat.toInt // 55 ss = ff.toString + "-----" + ii.toString // "55.0099983215332-----55" ss = "" + ff + "-----" + ii // same // using format - similar to % in Python or sprintf in C ss = "%5.2f %10d" format(ff,ii) // "55.01 55" // use printf() as in C printf("%5.2f %10d", ff,ii)
--
// checking type
def getInteger(obj: Any) = obj match {
  case n: Number => n.longValue
  case b: Boolean => if(b) 1L else 0L
  case s: String if s.length != 0 && s != "null" => s.toLong
  case _ => null
}
// http://stackoverflow.com/questions/19386964/i-want-to-get-the-type-of-a-variable-at-runtime

// testing if two variables point to the same object (or equal for primitive types)

def refEquals(a: Any, b: Any) = a match {   
  case x: Boolean if b.isInstanceOf[Boolean] => x == b   
  case x: Byte    if b.isInstanceOf[Byte]    => x == b   
  case x: Short   if b.isInstanceOf[Short]   => x == b
  case x: Char    if b.isInstanceOf[Char]    => x == b 
  case x: Int     if b.isInstanceOf[Int]     => x == b   
  case x: Float   if b.isInstanceOf[Float]   => x == b   
  case x: Double  if b.isInstanceOf[Double]  => x == b   
  case x: Long    if b.isInstanceOf[Long]    => x == b   
  case _ => a.asInstanceOf[AnyRef] eq b.asInstanceOf[AnyRef] 
}

// http://stackoverflow.com/questions/8087066/method-to-check-reference-equality-for-any-type
// http://www.slideshare.net/knoldus/object-equality-inscala
// http://www.artima.com/pins1ed/object-equality.html - very good article discussing how to define custom
equals() method to avoid problems when placing objects into collections, subclassing, etc.

Scala doesn't have primitive types, all types are objects.
It has same data types as Java:
      Byte, Short, Int, Long, Float, Double, Char, String, Boolean

also:

// char,string, multiline-string:
'\n' - char
"\n" - string
""" multiline
    string"""

Access Modifiers - private, protected, public (default is public)

// if/else:
if( x == 10 ){
  println("10");
}else if( x == 20 ){
  println("Value of X is 20");
}else{
  println("This is else statement");
}
--
// loops: 
while (condition) { ... }
do { ... } while (condition) for (var x <- 1 to 10) { ... } // 1 ... 10 for (var x <- 1 until 10) { ... } // 1 ... 9 for( a <- 1 to 3; b <- 1 to 3) { ... }
val numList = List(1,2,3,4,5);
for( a <- numList ){ ... } for( a <- numList if a != 3; if a < 8 ){ println( "Value of a: " + a ); } // return values from a for() loop through a function using yield: var retVal = for{ var x <- List if condition ... } yield x // breaking out of a loop // http://stackoverflow.com/questions/2742719/how-do-i-break-out-of-a-loop-in-scala import scala.util.control._ val br1 = new Breaks; val br2 = new Breaks; br1.breakable { for(a <- myList1){ ... br2.breakable { for( b <- myList2){ ... if( ... ){ br2.break; } } // for } // br2.breakable } // for } // br1.breakable

functions ------------------------------

functions

// function definition (parameters, return_type, and return_expression are optional):

def myFunc ([parameters]) : [return_type] = {
   statements
   return [expr]
}

// function working with specific types
def addInt( a:Int, b:Int ) : Int = {
  var sum:Int = 0
  sum = a + b
  return sum
}

// if no return statement - the result of last executed statement is returned
def addInt( a:Int, b:Int ) : Int = {
  a + b
}

// function working with different types
// http://stackoverflow.com/questions/4056452/how-do-i-implement-a-generic-mathematical-function-in-scala
// http://stackoverflow.com/questions/485896/how-does-one-write-the-pythagoras-theorem-in-scala
def addAny[T](a:T, b:T)(implicit num: Numeric[T]): T = {
  import num._
  var sum: T = a
  sum = a + b
  return sum
}

// void function (type "Unit")
def printMe( ) : Unit = {
  println("Hello, Scala!")
}
--
// anonymous functions and closures:
var factor = 4
val myMult = (i:Int) => i * factor

println("myMult(2) value = " +  myMult(2)) // 8
println("myMult(3) value = " +  myMult(3)) // 12


      

strings ------------------------------

More about strings

// strings: 
var aa = "AA" var aa:String = "AA" aa.concat("BB") // "AABB" aa + "BB" // "AABB" aa.length() // 2 aa.toLowerCase() // "aa" etc. etc. scala String is same as java.lang.String, so it understands many java methods:
char charAt(int index)
Returns the character at the specified index.
2 int compareTo(Object o)
Compares this String to another Object.
3 int compareTo(String anotherString)
Compares two strings lexicographically.
4 int compareToIgnoreCase(String str)
Compares two strings lexicographically, ignoring case differences.
5 String concat(String str)
Concatenates the specified string to the end of this string.
6 boolean contentEquals(StringBuffer sb)
Returns true if and only if this String represents the same sequence of characters as the specified StringBuffer.
7 static String copyValueOf(char[] data)
Returns a String that represents the character sequence in the array specified.
8 static String copyValueOf(char[] data, int offset, int count)
Returns a String that represents the character sequence in the array specified.
9 boolean endsWith(String suffix)
Tests if this string ends with the specified suffix.
10 boolean equals(Object anObject)
Compares this string to the specified object.
11 boolean equalsIgnoreCase(String anotherString)
Compares this String to another String, ignoring case considerations.
12 byte getBytes()
Encodes this String into a sequence of bytes using the platform's default charset, storing the result into a new byte array.
13 byte[] getBytes(String charsetName
Encodes this String into a sequence of bytes using the named charset, storing the result into a new byte array.
14 void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
Copies characters from this string into the destination character array.
15 int hashCode()
Returns a hash code for this string.
16 int indexOf(int ch)
Returns the index within this string of the first occurrence of the specified character.
17 int indexOf(int ch, int fromIndex)
Returns the index within this string of the first occurrence of the specified character, starting the search at the specified index.
18 int indexOf(String str)
Returns the index within this string of the first occurrence of the specified substring.
19 int indexOf(String str, int fromIndex)
Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.
20 String intern()
Returns a canonical representation for the string object.
21 int lastIndexOf(int ch)
Returns the index within this string of the last occurrence of the specified character.
22 int lastIndexOf(int ch, int fromIndex)
Returns the index within this string of the last occurrence of the specified character, searching backward starting at the specified index.
23 int lastIndexOf(String str)
Returns the index within this string of the rightmost occurrence of the specified substring.
24 int lastIndexOf(String str, int fromIndex)
Returns the index within this string of the last occurrence of the specified substring, searching backward starting at the specified index.
25 int length()
Returns the length of this string.
26 boolean matches(String regex)
Tells whether or not this string matches the given regular expression.
27 boolean regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len)
Tests if two string regions are equal.
28 boolean regionMatches(int toffset, String other, int ooffset, int len)
Tests if two string regions are equal.
29 String replace(char oldChar, char newChar)
Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.
30 String replaceAll(String regex, String replacement
Replaces each substring of this string that matches the given regular expression with the given replacement.
31 String replaceFirst(String regex, String replacement)
Replaces the first substring of this string that matches the given regular expression with the given replacement.
32 String[] split(String regex)
Splits this string around matches of the given regular expression.
33 String[] split(String regex, int limit)
Splits this string around matches of the given regular expression.
34 boolean startsWith(String prefix)
Tests if this string starts with the specified prefix.
35 boolean startsWith(String prefix, int toffset)
Tests if this string starts with the specified prefix beginning a specified index.
36 CharSequence subSequence(int beginIndex, int endIndex)
Returns a new character sequence that is a subsequence of this sequence.
37 String substring(int beginIndex)
Returns a new string that is a substring of this string.
38 String substring(int beginIndex, int endIndex)
Returns a new string that is a substring of this string.
39 char[] toCharArray()
Converts this string to a new character array.
40 String toLowerCase()
Converts all of the characters in this String to lower case using the rules of the default locale.
41 String toLowerCase(Locale locale)
Converts all of the characters in this String to lower case using the rules of the given Locale.
42 String toString()
This object (which is already a string!) is itself returned.
43 String toUpperCase()
Converts all of the characters in this String to upper case using the rules of the default locale.
44 String toUpperCase(Locale locale)
Converts all of the characters in this String to upper case using the rules of the given Locale.
45 String trim()
Returns a copy of the string, with leading and trailing whitespace omitted.
46 static String valueOf(primitive data type x)
Returns the string representation of the passed data type argument.
--

Array ------------------------------

Array - fixed nubmer of elements (variables) of the same type.

// Array:
var aa = Array(11,22,33)                // Array[String]
var aa = Array("mama", "papa123", null) // Array[String]
var aa = new Array[String](3)           // Array[String] = Array(null, null, null)
aa(0) = "mama"
aa(1) = "papa123"
aa(2) = "dada4"
for (ii <- 0 to (aa.length - 1))  println(aa(ii))

// concatenate arrays
var aa = Array(1,2,3)
var bb = Array(4,5)
var cc = concat(aa,bb)  // Array(1, 2, 3, 4, 5)

// multi-dimensional array = array of arrays
import Array._
var mm = ofDim[Int](3,3)
for (ii <- 0 to 2) {
  for ( jj <- 0 to 2) {
    mm(ii)(jj) = ii + jj;
  }
}

// using range() function
import Array._
var aa = range(0,5)    // Array[Int] = Array(0, 1, 2, 3, 4)
var aa = range(0,5,2)  // Array[Int] = Array(0, 2, 4)
var aa = range(5,0,-1) // Array[Int] = Array(5, 4, 3, 2, 1)

// creating array of objects using apply():
import Array._
var aa = apply(1,2,3)

// copy elements from src into dest array:
// copy(src, srcPos, dest, destPos, length)
import Array._
var aa = range(0,3)   // Array(0, 1, 2)
var bb = range(10,15) // Array(10, 11, 12, 13, 14)
copy(aa, 1, bb, 2, 2) // Array(10, 11, 1, 2, 14)

// create an empty array of a given type
var aa = Array.empty[Float]  // Array[Float] = Array()

// apply a function repeatedly - return Array of progressive results
// Array.iterate(start_val, num_steps)(func) 
Array.iterate(10, 3)(_ + 2)      // Array(10, 12, 14)
Array.iterate(1, 5)(2 * _)       // Array(1, 2, 4, 8, 16)
Array.iterate(1, 5)(n => 2 * n)  // Array(1, 2, 4, 8, 16)

// fill array with some computed values
Array.fill(3){ "%.3f" format (math.random) } // Array[String] = Array(0.722, 0.079, 0.421)


// Note - you can use Array.fill(M,N)(func) to fill in 2-dimensional array

// fill Array applying simple function to indexes
Array.tabulate(3)(_ + 3.1)   // Array(3.1, 4.1, 5.1)
Array.tabulate(4)(_*2)       // Array(0, 2, 4, 6)
Array.tabulate(2,3)(_ + 3*_) // Array(Array(0, 3, 6), Array(1, 4, 7))
    
--

collections - List ------------------------------

Collections - List

// List
List(1,2,3,4) // immutable linked list
List()  // empty list
Nil // empty list
val zeros = List.fill(10)(0.0)  // create list of 10 elements - and fill with 0.0
val squares = List.tabulate(6)(n => n * n) // List(0, 1, 4, 9, 16, 25)
List("AA", "BB", "CC")
var aa = "AA" :: "BB" :: "CC" :: Nil  // List("AA", "BB", "CC")
aa(2)  // third element of the list

var bb = List("a", "b")
var cc = List("c", "d")
bb ++ cc   // concatenate two lists together
bb ::: cc  // same
Lisc.concat(bb,cc)  // same

// count elements whic satisfy a criterium
var aa = List("a","bc","def") aa.count(s => s.length >= 2) // 2 aa.drop(2) // return list without firt 2 elements aa.dropRight(2) // return list without last 2 elements aa.exists(s => s == "bc") aa.filter(s => s.length == 2) aa.forall(s => s.endsWith("c")) aa.foreach(s => println(s)) for (s <- aa) println(s) aa.foreach(println) aa.head // first element aa.tail // all list except 1st element aa.last // last element aa.init // all list except last element aa.isEmpty aa.length aa.map(s => s + " mama") aa.mkString(", ") / join elements aa.remove(s => s.length == 4) aa.reverse aa.sort((s, t) => s.charAt(0).toLower < t.charAt(0).toLower) // remove duplicates var aa=List(1,1,2,2) var bb=aa.distinct // List(1,2) // check if the list is sorted incrementally if(myList.sliding(2).forall(x=>x(1) >= x(0))) println("sorted") else println("not")

collections - Set ------------------------------

Collections - Set

// Set - elements of the same type, no duplicates, no guaranteed order
var nums1 = Set(2,3,4,5) // immutable Set (no duplicates)
import scala.collection.mutable.Set  // switch to mutable sets
var nums2 = Set(2,3,4,5)  // mutable set

nums1.head  // get one (first) element
nums1.tail  // get a Set of all other elements
nums1.last  // last element
nums1.init  // get a Set of all elements except last

// Empty set of integer type
var ss : Set[Int] = Set()
ss.isEmpty  // true

// combining two sets:
s1 ++ s2
s1.++(s2)
s1 | s2

// find max or min:
s1.max
s1.min

// find intersection of two sets
s1 & s2
s1.&(s2)
s1.intersect(s2)

// find differenece between sets
s2 &~ s1  // same as s2 diff s1
s1 &~ s2  // same as s1 diff s2

// check is one set is a subset of another
s2 subsetOf s1

// add or remove an element (creates a new set)
s1 + 55
s1 - 2

// check if element is in the Set:
s1.contains(2)
s1.apply(1)
s1.exists(_ > 0)

// length of the set
s1.size

// count number of elements satisfying some criteria
s1.count(_>=1)

// copy elements to array
s1.copyToArray(arr, arr_start, len)

// check if two sets are the same
var s1 = Set(1,2,3)
var s2 = Set(3,2,1)
s1 == s2 // true (actually compares values)
s1 eq s2 // false (compares if ref. point to the same object)

// more methods
drop
dropRight
dropWhile
filter(_ > 0)
find(_ > 0)  // returns first element which satisfies
forall(_ > 0) // tests for all elements
foreach()
iterator
map
mkString // all elements as a string
mkString("|")
toString
toSeq
toList
toMap
toBuffer
toArray
take(2) / get 2 elements
product // product of all elements
sum // sum of all elements
splitAt(5) // splits a set into 2 (5 and N-5 elements) 
take(5) // first 5 elements
takeRight(5) // last 5 elements
      

collections - Map ------------------------------

Collections - Map

// Map (dictionary, hash) - by default immutable (can add elements, but can not remove them)
import scala.collection.mutable.Map   // switch to mutable Maps
var xx = Map("k1" -> 1, "k2" -> 2, "k3" -> 3)
xx.keys
xx.values xx.keys.foreach{ kk => print("Key = " + kk) println(", Val = " + xx(kk)) } if (xx.contains("k1")) print("found the key") xx += ("k4" -> 44) // add a key/value pair xx.remove("k4") // remove key/value pair xx = Map() // empty the map // concatenating two maps: m1 ++ m2 m1.++(m2) // sorting - get a sorted list of keys var sorted_keys = xx.keysIterator.toList.sorted // List(k1, k2, k3) var sorted_values = xx.valuesIterator.toList.sorted // List(1, 2, 3) // sorting by keys using custom sorting function xx.toSeq.sortWith(_._1 < _._1) // ArrayBuffer((k1,1), (k2,2), (k3,3)) // sorting by values ... xx.toSeq.sortWith(_._2 < _._2) // ArrayBuffer((k1,1), (k2,2), (k3,3)) // or xx.toSeq.sortBy(_._1) xx.toSeq.sortBy(_._2) // or use TreeMap import scala.collection.immutable.TreeMap TreeMap(xx.toSeq:_*) // Map(k1 -> 1, k2 -> 2, k3 -> 3) // or use SortedMap import collection.immutable.SortedMap val sorted = SortedMap.empty[String, Int] ++ xx

collections - Tuple ------------------------------

Collections - Tuple

// Tuple - can hold objects of different types, but not more than 22 of them
val xx = (10, "Hello", 5.5)  // Tuple3[Int, String, Double]

// accessing elements of a tuple
xx._1
xx._2
etc.

// looping through a tuple:
xx.productIterator.foreach{ i =>println("Value = " + i )}
Value = 10
Value = Hello
Value = 5.5

// string representation
xx.toString  // "(10,Hello,5.5)"

collections - Option ------------------------------

Collections - Option

// Option - container for zero or one element of a given type
val x:Option[Int] = Some(5)
// An Option[T] can be either Some[T] or None object, which represents a missing value. 

// getOrElse or isEmpty methods:
a.getOrElse(0)   // will return 0 instead of None
isEmpty          // true or false

// option methods:
get // returns the value (or None)
isEmpty
exists(_ > 2)
filter(_ > 2)
filterNot(_ > 2)
flatMap
foreach
getOrElse
isDefined
iterator
map
orElse
orNull

Iterator ------------------------------

Iterator

// Iterator - not a collection, but rather a way to access the elements of a collection one by one
val it = Iterator("a", "number", "of", "words")
while (it.hasNext){
  println(it.next())
}

// methods
it.max
it.min
it.size
it.length
it1.++(it2)
addString(sb)
addString(sb,"|")
buffered
contains
copyToArray(arr, arr_start, len)
count(_ > 2)
drop(5)
dropWhile(_ > 2)
duplicate
exists
filter
filterNot
find
flatMap
forall
foreach
hasDefiniteSize
indexOf
indexWhere
isEmpty
isTraversableAgain
length
map
max
min
mkString
mkString("|")
nonEmpty
padTo
patch
product
sameElements
seq
size
slice
sum
take
toArray
toBuffer
toIterable
toIterator
toList
toMap
toSeq
toString()
zip
--

Classes ------------------------------

Classes

// classes and objects: 
      
import java.io._

class Point(val xc: Int, val yc: Int) {
   var x: Int = xc
   var y: Int = yc
   def move(dx: Int, dy: Int) {
      x = x + dx
      y = y + dy
      println ("Point x location : " + x);
      println ("Point y location : " + y);
   }
}

class Location(override val xc: Int, override val yc: Int,
   val zc :Int) extends Point(xc, yc){
   var z: Int = zc

   def move(dx: Int, dy: Int, dz: Int) {
      x = x + dx
      y = y + dy
      z = z + dz
      println ("Point x location : " + x);
      println ("Point y location : " + y);
      println ("Point z location : " + z);
   }
}


object Test {
   def main(args: Array[String]) {
      val pt = new Location(10, 20, 30); // created an object
      pt.move(10, 11, 12);               // invoke a method
   }
}      



      
--
// Singleton objects:
// In Scala we cannot have static members.
// Instead, Scala has singleton objects. 
// Just put the constructor code in the body of the object definition:

object MyObject {
  println("Hello") // This will print hello the first time
                   // the Foo object is accessed (and only
                   // that once).
}
--
// A trait is similar to interface in Java.
// A trait may contain method and field definitions
// A class can extend multiple traits
// A trait definition looks like class definition (but using word "trait" instead of "class", 
// and a trait can not have constructor parameters)
// note - if you expect inheriting from it in Java code, 
// or expect outside groups to inherit from it, 
// or need performance - it is better to use classes than traits.

trait Equal {
  def isEqual(x: Any): Boolean
  def isNotEqual(x: Any): Boolean = !isEqual(x)
}

class Point(xc: Int, yc: Int) extends Equal {
  var x: Int = xc
  var y: Int = yc
  def isEqual(obj: Any) =
    obj.isInstanceOf[Point] &&
    obj.asInstanceOf[Point].x == x
}

--

Matching ------------------------------

xxxxxxx

// match:
def matchTest(x: Any): String = {
  var aa = x match {
    case 1      => "one"
    case "two"  => "two2"
    case y: Int => "scala.Int"  // testing type
    case _      => "many"       // default
  }
  return " " + x + " " + aa
}

// match using "case" Classes:

val p1 = new Person("name1", 25)
val p2 = new Person("name2", 35) 
for (person <- List(p1,p2)) {
  person match {
    case Person("name1", 25) => println("p1")
    case Person(name, age) =>
      println("Age: " + age + " year, name: " + name + "?")
  }
}

// prepending the "case" before a class name does the following:
// compiler automatically converts the constructor arguments
// into immutable fields, it automatically implements equals,
// hashCode, and toString methods to the class.
--
// regex matching:
// when defining regex, use raw strings (""")
val ss = """\.+((xyz)|(abc))""" // String = \.+((xyz)|(abc))

// adding .r at the end of the script creates a Regex object
import scala.util.matching.Regex
val ss = """\.+((xyz)|(abc))""".r  // scala.util.matching.Regex = \.+((xyz)|(abc))

// use Regex constructor explicitly
import scala.util.matching._
val Name = new Regex("""(\w+)\s+(\w+)""")  // scala.util.matching.Regex = (\w+)\s+(\w+)

// use .matches() method
"mama papa dada".matches("(?i).*\\sPAPA\\s.*")   // true

// ways to match / replace:

// regex findFirstIn  mystr
// regex replaceFirstIn(mystr, "mama")
// regex findAllIn    mystr  - returns an iterator over the matches.  
// regex replaceAllIn(mystr, "mama")
// Example:
"l|he".r findAllIn "hello xyz" foreach {println _}
he
l
l


("(h)(e)|(l)".r findAllIn "hello xyz").matchData foreach { m => println(m.start, m.end, m.before, m.after, m.source)}
(0,2,,llo xyz,hello xyz)
(2,3,he,lo xyz,hello xyz)
(3,4,hel,o xyz,hello xyz)


val date = "11/01/2010"
val DateRegex = """(\d\d)/(\d\d)/(\d\d\d\d)""".r
Date: scala.util.matching.Regex = (\d\d)/(\d\d)/(\d\d\d\d)
val Date(day, month, year) = date          
println(day)   // 11
println(month) // 01
println(year)  // 2010

Some examples were taken from these posts:
// http://daily-scala.blogspot.com/2010/01/regular-expression-1-basics-and.html
// http://daily-scala.blogspot.com/2010/01/regular-expression-2-rest-regex-class.html
// http://daily-scala.blogspot.com/2010/01/regular-expression-3-regex-matching.html

exceptions ------------------------------

exceptions

// exceptions:
// try{}catch{}finaly{} blocks like in Java, 
// but the "catch" block uses matching to identify and handle the exceptions.
// You can also "throw" exceptions (like in java)

import java.io.FileReader
import java.io.FileNotFoundException
import java.io.IOException

object Test {
   def main(args: Array[String]) {
      try {
         val f = new FileReader("input.txt")
      } catch {
         case ex: FileNotFoundException => {
            println("Missing file exception")
         }
         case ex: IOException => {
            println("IO Exception")
         }
      } finally {
         println("Exiting finally...")
      }
   }
}

misc ------------------------------

misc

 

// exctractor: 
// extractor is an object with method unapply() to match 
// a value and take it apart.
--
// reading directory:
import java.io.File
var allFiles = new File(myDirectoryPath).listFiles
var textFiles = allFiles.filter(_.getName.endsWith(".txt"))
var text_fnames = textFiles.map(_.getName)
--
// reading lines from file:
import scala.io.Source
val lines = Source.fromFile(someFileName).getLines()
var mylines = lines.toList
--
// Currying: 
// http://www.ibm.com/developerworks/library/j-ft10/ """Currying is a feature of many functional languages.
Named after mathematician Haskell Curry
(for whom the Haskell programming language is also named),
currying transforms a multiargument function so that it can be called
as a chain of single-argument functions."""
--
// scala.concurrent
// Explore Scala concurrency 
// - http://www.ibm.com/developerworks/java/library/j-scala02049/index.html
// Dive deeper into Scala concurrency 
// - http://www.ibm.com/developerworks/java/library/j-scala04109/index.html
// (actor based message passing model)
--
// processing command line arguments:

object Lev1 {
def main(args: Array[String]) = {
args.foreach(arg => println("arg = " + arg))
}
} // or if running a scala script, you can do simply use array args: args.foreach(arg => println("arg = " + arg))
// http://alvinalexander.com/scala/scala-shell-script-command-line-arguments-args // http://alvinalexander.com/scala/scala-shell-script-example-exec-syntax // http://stackoverflow.com/questions/2315912/scala-best-way-to-parse-command-line-parameters-cli
-- --
// SBT (Simple Build Tool): 
- an open source build tool for Scala and Java projects.
- build descriptions written in Scala using a DSL
- integrated Scala interpreter for rapid debugging
--
// running system commands
import scala.sys.process._ var aa = "/usr/bin/true" .! // 0 var aa = "/usr/bin/false" .! // 1 "ls -alF" .! // prints output var dirContents = "ls -alF".!! // output in a variable // http://www.scala-lang.org/files/archive/nightly/docs/library/#scala.sys.process.package
--
// speed considerations - loops or recursion
// http://stackoverflow.com/questions/15138624/scala-recursion-vs-loop-performance-and-runtime-considerations
// while loops and tail recursion are the same speed and fast
// regular recursion and for-loops are slower.
// (Regular recursion may not be slower if the JVM optimization makes it equivalent)
--
// write to file:
import java.io._
val writer = new PrintWriter(new File("test.txt" ))
writer.write("Hello Scala")
writer.close()

// read from file
import scala.io.Source
Source.fromFile("test.txt" ).foreach{ print }

// receive line from console screen
print("Enter line : " )
val line = Console.readLine
println("You entered: " + line)
--
// xxxxx: 
xxxxxxx
--
// xxxxx: 
xxxxxxx