Scala tutorial for Java programmers with examples

Control Structures#

Scala’s control structures are if, while, for, try, match, and function calls. In Scala, control structures return values like functions.

The if expression has the following syntax:

User-defined functions#

We can define functions in Scala. Take a look at this example, which takes two integers and returns their sum:

Note: You can choose not to use the curly brackets if the function’s body only consists of a single expression.

Objects and Classes in Scala#

Unlike Java, which distinguishes primitive and reference types, Scala treats everything as an object, since Scala is a pure OOP language. In Scala, numbers are also treated as objects, so they also have methods. Take the following arithmetic expression:

1 + 2 * 3 / x

This expression is made with method calls since it is the same as the following expression, so + and * are valid identifiers in Scala.

1.+(2.*(3)./(x))

Classes#

In Scala, classes are declared much like Java, but Scala classes can have parameters. Look at this basic class definition in Scala using the class keyword and var keyword to define our properties (called fields in Scala).

class Person{
  var name: String = "temp"
  var gender: String = "temp"
  var age: Int = 0
}

To define the methods of our class, we use this syntax:

class Person{
  var name: String = "temp"
  var gender: String = "temp"
  var age: Int = 0

  def walking = println(s"$name is walking")

  def talking = println(s"$name is talking")

}

And now we can create instances of our classes using val.

// Creating an object of the Person class
val firstPerson = new Person 

firstPerson.name = "Mary"
firstPerson.gender = "female"
firstPerson.age = 25


println(firstPerson.name)
println(firstPerson.gender)
println(firstPerson.age)

Calling functions within functions#

In Scala, functions are also treated as objects, so we can pass functions as arguments, store them in variables, or return them from other functions. This is one valuable feature of functional programming that Scala provides.

Take a look at this example below where we are calling the function square in the other function SquareSum.

Inheritance and Overriding#

There are several types of inheritance supported by Scala:

• Single-level Inheritance: One class inherits from a single other class
• Multilevel Inheritance: One class extends another which then extends another
• Multiple Inheritance: One class inherits from multiple base classes

In Scala, all classes inherit from a superclass, and when no superclass is declared, Scala uses scala.AnyRef. You can override methods that are inherited from a superclass, but you must explicitly specify this using the override modifier. For example:

class Complex(real: Double, imaginary: Double) {
  def re = real
  def im = imaginary
  override def toString() =
    "" + re + (if (im >= 0) "+" else "") + im + "i"
}

Traits with Scala#

Scala uses Traits, which are similar to Java interfaces. Much like inheritance with Scala like above, a class can also import code from one or more traits. When this happens, a class implements the given trait’s interface and all code in that trait.

Think of this as a way to implement reusable behavior in Scala code.

The basic properties of a Trait are:

• Traits specify the signature of the methods that a given supports.
• Traits are declared like classes with the trait keyword Take a look at this example:

trait Iterator[A] {
  def hasNext: Boolean
  def next(): A
}

In Scala, we can use the extends keyword to extend a trait. Then, we implement any abstract members with the override keyword:

Next steps for your Scala journey#

Congrats on making it to the end. You’re now well on your way to transitioning to being a Scala developer. As you can see, Scala empowers you to utilize your existing Java skills. There is still a lot to learn about Scala, and hands-on practice will be essential to mastering this language.

For next steps, we recommend the following concepts:

• Generics with Scala
• Higher-order functions
• Currying
• Scala’s Collection Library

To get started with these concepts and start building with Scala, check out Educative’s course Learn Scala from Scratch. This course will help you stay ahead of the curve, make awesome, scalable apps, and learn a highly coveted new programming language. By the end, you’ll be fully transitioned from Java to Scala!

Happy learning!

Continue learning about Scala and Java#

• Scala 101: a beginner’s guide to the scalable language
• What is functional programming? Explained in Python, JS, and Java
• The resurgence of Scala in 2020