Scala - Quick Guide

Scala - Overview

Scala, short for Scalable Language, is a hybrid functional programming language. It was created by Martin Odersky. Scala smoothly integrates the features of object-oriented and functional languages. Scala is compiled to run on the Java Virtual Machine.
Many existing companies, who depend on Java for business critical applications, are turning to Scala to boost their development productivity, applications scalability and overall reliability.Many existing companies, who depend on Java for business critical applications, are turning to Scala to boost their development productivity, applications scalability and overall reliability.
Here we have presented a few points that makes Scala the first choice of application developers.

Scala is object-oriented

Scala is a pure object-oriented language in the sense that every value is an object. Types and behavior of objects are described by classes and traits which will be explained in subsequent chapters.
Classes are extended by subclassing and a flexible mixin-based composition mechanism as a clean replacement for multiple inheritance.

Scala is functional

Scala is also a functional language in the sense that every function is a value and every value is an object so ultimately every function is an object.
Scala provides a lightweight syntax for defining anonymous functions, it supports higher-order functions, it allows functions to be nested, and supports currying. These concepts will be explained in subsequent chapters.

Scala is statically typed

Scala, unlike some of the other statically typed languages (C, Pascal, Rust, etc.), does not expect you to provide redundant type information. You don't have to specify a type in most cases, and you certainly don't have to repeat it.

Scala runs on the JVM

Scala is compiled into Java Byte Code which is executed by the Java Virtual Machine (JVM). This means that Scala and Java have a common runtime platform. You can easily move from Java to Scala.
The Scala compiler compiles your Scala code into Java Byte Code, which can then be executed by the 'scala' command. The 'scala' command is similar to the java command, in that it executes your compiled Scala code.

Scala can Execute Java Code

Scala enables you to use all the classes of the Java SDK and also your own custom Java classes, or your favorite Java open source projects.

Scala can do Concurrent & Synchronize processing

Scala allows you to express general programming patterns in an effective way. It reduces the number of lines and helps the programmer to code in a type-safe way. It allows you to write codes in an immutable manner, which makes it easy to apply concurrency and parallelism (Synchronize).

Scala vs Java

Scala has a set of features that completely differ from Java. Some of these are −

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

Scala Web Frameworks

Scala is being used everywhere and importantly in enterprise web applications. You can check a few of the most popular Scala web frameworks −

• The Lift Framework
• The Play framework
• The Bowler framework

Scala - Environment Setup

Try it Option Online

We have set up the Scala Programming environment on-line, so that you can compile and execute all the available examples on line. It gives you confidence in what you are reading and enables you to verify the programs with different options. Feel free to modify any example and execute it on-line.
Try the following example using our on-line compiler available at CodingGround.

object HelloWorld {
   def main(args: Array[String]) {
      println("Hello, world!")
   }
}

For most of the examples given in this tutorial, you will find a Try it option in our website code sections at the top right corner that will take you to the online compiler. So just make use of it and enjoy your learning.

Scala can be installed on any UNIX flavored or Windows based system. Before you start installing Scala on your machine, you must have Java 1.8 or greater installed on your computer.
Follow the steps given below to install Scala.

Step 1: Verify Your Java Installation

First of all, you need to have Java Software Development Kit (SDK) installed on your system. To verify this, execute any of the following two commands depending on the platform you are working on.
If the Java installation has been done properly, then it will display the current version and specification of your Java installation. A sample output is given in the following table.

Platform	Command	Sample Output
Windows	Open Command Console and type − \>java –version	Java version "1.8.0_31" Java (TM) SE Run Time Environment (build 1.8.0_31-b31) Java Hotspot (TM) 64-bit Server VM (build 25.31-b07, mixed mode)
Linux	Open Command terminal and type − $java –version	Java version "1.8.0_31" Open JDK Runtime Environment (rhel-2.8.10.4.el6_4-x86_64) Open JDK 64-Bit Server VM (build 25.31-b07, mixed mode)

We assume that the readers of this tutorial have Java SDK version 1.8.0_31 installed on their system.
In case you do not have Java SDK, download its current version from http://www.oracle.com/technetwork/java/javase/downloads/index.html and install it.

Step 2: Set Your Java Environment

Set the environment variable JAVA_HOME to point to the base directory location where Java is installed on your machine. For example,

Sr.No	Platform & Description
1	Windows Set JAVA_HOME to C:\ProgramFiles\java\jdk1.7.0_60
2	Linux Export JAVA_HOME=/usr/local/java-current

Append the full path of Java compiler location to the System Path.

Sr.No	Platform & Description
1	Windows Append the String "C:\Program Files\Java\jdk1.7.0_60\bin" to the end of the system variable PATH.
2	Linux Export PATH=$PATH:$JAVA_HOME/bin/

Execute the command java -version from the command prompt as explained above.

Step 3: Install Scala

You can download Scala from http://www.scala-lang.org/downloads. At the time of writing this tutorial, I downloaded ‘scala-2.11.5-installer.jar’. Make sure you have admin privilege to proceed. Now, execute the following command at the command prompt −

Platform	Command & Output	Description
Windows	\>java –jar scala-2.11.5-installer.jar\>	This command will display an installation wizard, which will guide you to install Scala on your windows machine. During installation, it will ask for license agreement, simply accept it and further it will ask a path where Scala will be installed. I selected default given path “C:\Program Files\Scala”, you can select a suitable path as per your convenience.
Linux	Command − $java –jar scala-2.9.0.1-installer.jar Output − Welcome to the installation of Scala 2.9.0.1! The homepage is at − http://Scala-lang.org/ press 1 to continue, 2 to quit, 3 to redisplay 1................................................ [ Starting to unpack ] [ Processing package: Software Package Installation (1/1) ] [ Unpacking finished ] [ Console installation done ]	During installation, it will ask for license agreement, to accept it type 1 and it will ask a path where Scala will be installed. I entered /usr/local/share, you can select a suitable path as per your convenience.

Finally, open a new command prompt and type Scala -version and press Enter. You should see the following −

Platform	Command	Output
Windows	\>scala -version	Scala code runner version 2.11.5 -- Copyright 2002-2013, LAMP/EPFL
Linux	$scala -version	Scala code runner version 2.9.0.1 – Copyright 2002-2013, LAMP/EPFL

Scala - Basic Syntax

If you have a good understanding on Java, then it will be very easy for you to learn Scala. The biggest syntactic difference between Scala and Java is that the ';' line end character is optional.
When we consider a Scala program, it can be defined as a collection of objects that communicate via invoking each other’s methods. Let us now briefly look into what do class, object, methods and instance variables mean.

• Object − Objects have states and behaviors. An object is an instance of a class. Example − A dog has states - color, name, breed as well as behaviors - wagging, barking, and eating.
• Class − A class can be defined as a template/blueprint that describes the behaviors/states that are related to the class.
• Methods − A method is basically a behavior. A class can contain many methods. It is in methods where the logics are written, data is manipulated and all the actions are executed.
• Fields − Each object has its unique set of instance variables, which are called fields. An object's state is created by the values assigned to these fields.
• Closure − A closure is a function, whose return value depends on the value of one or more variables declared outside this function.
• Traits − A trait encapsulates method and field definitions, which can then be reused by mixing them into classes. Traits are used to define object types by specifying the signature of the supported methods.

First Scala Program

We can execute a Scala program in two modes: one is interactive mode and another is script mode.

Interactive Mode

Open the command prompt and use the following command to open Scala.

\>scala

If Scala is installed in your system, the following output will be displayed −

Welcome to Scala version 2.9.0.1
Type in expressions to have them evaluated.
Type :help for more information.

Type the following text to the right of the Scala prompt and press the Enter key −

scala> println("Hello, Scala!");

It will produce the following result −

Hello, Scala!