Getting started with Scala

This post is not to teach scala but a small reference for what I am going to learn about Scala. I am referring to the book “Programming in Scala”.

Feel free to look at small code snippets I used to get started with JVM based OOP and functional programming language. I will start with Scala shell prompt.

1. val defines variables similar to final identifier in Java:

scala> val msg="Hello World"
msg: java.lang.String = Hello World
scala> println(msg)
Hello World
scala> msg="Hi"
<console>:5: error: reassignment to val 
msg="Hi" 
   ^ 
scala>

2. Print a value or variable using println():

scala> println("Hello Scala")
Hello Scala

scala> println(msg)
Hello World

3. Using variables:

scala> var msg="Hello Scala"
msg: java.lang.String = Hello Scala

scala> var msg2: java.lang.String = "Hello Scala with explicit data type"
msg2: java.lang.String = Hello Scala with explicit data type

4. Define Function:

scala> def max(x: Int, y: Int): Int = {
| if(x>y) x
| else y
| }
max: (Int,Int)Int
scala> max(5,8)
res13: Int = 8

def – keyword to define function
max – function name
x and y – Parameters to function max of type Int that maps to int(primitive data type) in Java
Int – Return type of the function

scala> def greet() = println("Hello, world!")
greet: ()Unit

scala> greet()
Hello, world!

scala> greet
Hello, world!

5. Scala Scripts

$ cat first_script.scala
println("Hello Scala from script")
$ scala first_script.scala
Hello Scala from script

Arguments to Scala script are made available in an array named args and elements are accessed using () as in older languages.

$ cat second_script.scala
// Comment in scala
println("Hello "+args(0))
$ scala second_script.scala Rasesh
Hello Rasesh
$ scala second_script.scala
java.lang.ArrayIndexOutOfBoundsException: 0
at Main$$anon$1.<init>((virtual file):6)
at Main$.main((virtual file):4)
at Main.main((virtual file))

6. Loops: while

$ cat 3_printargs.scala
var i=0
while(i<args.length){
println(args(i))
i+=1
}

$ scala 3_printargs.scala

$ scala 3_printargs.scala Hi Hello Scala
Hi
Hello
Scala

Note: i++ or ++i does not work in Scala as in Java

7. Loops: foreach and for

$ cat 4_foreach.scala
args.foreach(arg => println(arg))

$ scala 4_foreach.scala 1 2 3
1
2
3
$ cat 4_foreach.scala
args.foreach((arg:String) => println(arg))

$ scala 4_foreach.scala 1 2 3
1
2
3
$ cat 4_foreach.scala
args.foreach(println)

$ scala 4_foreach.scala 1 2 3
1
2
3

foreach accepts a function as an argument (functional programming aspect) and in each of 3 examples above, we passed a function to it and it executed it for each element in args array.

Imperative for:

$ cat 5_for.scala
for (arg <- args)
println(arg)

$ scala 5_for.scala 1 2 3
1
2
3

This was first glimpse of Scala and I will continue in other post as I try different things learning Scala.

This is helpful: http://docs.scala-lang.org/tutorials/scala-for-java-programmers.html

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