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Scala Tutorial Scala is a multi-paradigm programming language, designed to integrate various features of object-oriented programming and functional programming.

Scala is a multi-paradigm programming language, a programming language similar to Java, designed to implement a scalable language and integrate various features of object-oriented programming and functional programming.

The first Scala program

The following is a typical Hello World program written in Scala:

 object HelloWorld extends App {
   println("Hello, world!")
 }

or

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

Please note how it is similar to Java's Hello World application. One significant difference is that the Scala version of the Hello World program does not mark the main method as a static method through the static keyword, but uses the object keyword to create a singleton.

Assuming that the program is saved as a HelloWorld.scala file, it can then be compiled via the following command line:

> scalac HelloWorld.scala

To run:

> scala -classpath . HelloWorld

This is the same as compiling and running Java Isn’t the “Hello World” program very similar? In fact, Scala's compilation and execution model is equivalent to Java, so it is also compatible with Java's build tools, such as Ant.

You can also run the program directly using the Scala interpreter, using the option -i (load code from file) and option -e (to run additional code, you have to actually execute the method of the HelloWorld object):

> scala -i HelloWorld.scala -e 'HelloWorld.main(null)'

Tips: Our Scala tutorials will help you learn Scala from beginner to advanced level. If you have any questions, please go to the PHP Chinese website Scala Community to ask your questions, and enthusiastic netizens will answer them for you.

Scala Features

Supported Programming Paradigms

• Object-Oriented Features

Scala is A purely object-oriented language where every value is an object. The data type and behavior of an object are described by classes and traits. There are two ways to extend the class abstraction mechanism. One approach is subclass inheritance, and the other approach is a flexible mix-in mechanism. These two approaches can avoid the problems of multiple inheritance.

• Functional programming

Scala is also a functional language, and its functions can also be used as values. Scala provides a lightweight syntax for defining anonymous functions, supports higher-order functions, allows nesting of multiple levels of functions, and supports currying. Scala's case classes and their built-in pattern matching are equivalent to the algebraic types commonly used in functional programming languages.

Furthermore, programmers can use Scala's pattern matching to write code similar to regular expressions to process XML data. In these situations, list comprehension capabilities are useful for writing formulaic queries.

Since the JVM does not support tail recursion, Scala cannot fully support tail recursion optimization. However, the Scala compiler can optimize some simple tail recursions into loops.

The following code implements the quick sort algorithm in a functional style, which can be compared with the Erlang quick sort example:

def qsort(list: List[Int]): List[Int] = list match {
  case Nil => Nil
  case pivot :: tail =>
    val(smaller, rest) = tail.partition(_ < pivot)
    qsort(smaller) ::: pivot :: qsort(rest)
}

Static type

Scala has a type system, through Compilation time checks to ensure code security and consistency. The type system specifically supports the following features:

• Generic categories,

• Covariance and contravariance,

• Mark,

• Upper and lower bound constraints of type parameters,

• Treat categories and abstract types as object members,

• Composite type,

• Explicitly specify the type when referencing yourself,

• View,

• Polymorphic methods.

Extensibility

Scala is designed to adhere to the fact that in practice, domain-specific application development often requires language extensions specific to that domain. Scala provides many unique language mechanisms that make it easy and seamless to add new language constructs in the form of libraries:

• Any method can be used as a prefix or postfix operator,

• Closures can be automatically constructed based on the expected type.

Using the above two features in combination allows you to define new statements without extending the syntax or using metaprogramming features such as macros.

Concurrency

Scala uses Actor as its concurrency model. Actor is a thread-like entity that sends and receives messages through mailboxes. Actors can reuse threads, so millions of Actors can be used in the program, while threads can only create thousands. In versions after 2.10, Akka is used as its default Actor implementation. [20] The following code is an EchoServer implementation using Actor mode

val echoServer = actor(new Act {
  become {
    case msg => println("echo " + msg)
  }
})
echoServer ! "hi"

Actor mode can simplify concurrent programming and take advantage of the capabilities of multi-core CPUs.

Content covered by this Scala tutorial manual

This Scala tutorial covers all basic and advanced knowledge of Scala, including basic Scala syntax, Scala data types, Scala variables, Scala operators, Scala functions, Introduction to all basic and advanced knowledge of Scala such as Scala strings, Scala classes and objects, etc.

Tips: Each chapter of this tutorial contains many Scala examples. You can directly click the "Run Example" button to view the results online. These examples will help you better understand and use Scala.