Scala is a powerful and expressive programming language that combines object-oriented and functional programming features. Since you already know Java, learning Scala should be relatively smooth, as Scala runs on the Java Virtual Machine (JVM) and can seamlessly interoperate with Java.

Here's a brief introduction to Scala:

1. Hello World:

Let's start with a simple "Hello, World!" program. Create a file named HelloWorld.scala and add the following code:

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

2. Variables and Data Types:

Scala has a concise syntax for variable declaration and supports various data types:

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val x: Int = 10 // Immutable variable (similar to final in Java)
var y: String = "Scala" // Mutable variable

// Type inference can also be used
val z = 3.14 // Scala infers the type as Double

3. Functions:

Functions are fundamental in Scala, and you can define them using the def keyword:

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def add(x: Int, y: Int): Int = {
  x + y
}

val result = add(3, 5)
println(result)

4. Classes and Objects:

Scala supports both classes and objects. Objects are single instances of a class and are similar to Java's static methods.

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class Person(name: String, age: Int) {
  def display(): Unit = {
    println(s"Name: $name, Age: $age")
  }
}

val person = new Person("John", 25)
person.display()

5. Traits:

Traits are similar to interfaces in Java but can also include method implementations.

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trait Speaker {
  def speak(): Unit
}

class Dog extends Speaker {
  def speak(): Unit = {
    println("Woof!")
  }
}

val dog = new Dog()
dog.speak()

6. Pattern Matching:

Pattern matching is a powerful feature in Scala that allows concise and expressive code.

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def matchExample(x: Any): String = x match {
  case 1 => "One"
  case "hello" => "Greeting"
  case _: Double => "A Double value"
  case _ => "Unknown"
}

val result = matchExample("hello")
println(result)

7. Collections:

Scala has a rich set of collection classes. Here's an example of using a List:

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val numbers = List(1, 2, 3, 4, 5)
val doubled = numbers.map(_ * 2)
println(doubled)

8. Functional Programming:

Scala supports functional programming concepts like immutability, higher-order functions, and lambdas.

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val numbers = List(1, 2, 3, 4, 5)
val sum = numbers.reduce(_ + _)
println(sum)

9. Concurrency with Akka:

Akka is a popular actor-based concurrency framework in Scala. It helps build scalable and resilient systems.

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import akka.actor.{Actor, ActorSystem, Props}

class MyActor extends Actor {
  def receive: Receive = {
    case message: String => println(s"Received: $message")
  }
}

val system = ActorSystem("MySystem")
val myActor = system.actorOf(Props[MyActor], "myActor")

myActor ! "Hello, Akka!"

10. Type Parameterization:

Scala supports generics, allowing you to write generic classes and functions.

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class Box[A](value: A) {
  def getValue: A = value
}

val intBox = new Box(42)
val strBox = new Box("Scala")

println(intBox.getValue)
println(strBox.getValue)

These are just the basics, and Scala has many more features and concepts to explore. I recommend using the official Scala documentation and experimenting with code to deepen your understanding. Additionally, you can leverage your existing Java knowledge when working with Scala, as they can be easily integrated.