8.4. Scala basic syntax

8.4.1. The first Scala program #

$ scala Welcome to Scala version 2.11.7 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_31). Type in expressions to have them evaluated. Type :help for more information. scala> 1 + 1 res0: Int = 2 scala> println("Hello World!") Hello World! scala> 

8.4.2. Script form #

We can also create a HelloWorld.scala to execute the code HelloWorld.scala the code is as follows:

object HelloWorld { /* This is my first Scala program * The following program will output 'Hello World!' */ def main(args: Array[String]) { println("Hello, world!") // output Hello World } } 

Next, we use the scalac command to compile it:

$ scalac HelloWorld.scala $ ls HelloWorld$.class HelloWorld.scala HelloWorld.class 

After compiling, we can see the generation in the directory. HelloWorld.class file, which can be run on Java Virtual Machine (JVM).

After compilation, we can use the following command to execute the program:

$ scala HelloWorld Hello, world! 

8.4.3. Basic grammar #

The basic syntax of Scala should pay attention to the following points:

• Case sensitive-Scala is case sensitive, which means that identifying Hello and hello have different meanings in Scala.

• Class name-capitalize the first letter of all class names.

  If you need to use several words to form the name of a class, the first letter of each word should be capitalized.

  Example: class MyFirstScalaClass
• Method name-the first letter of all method names is lowercase.

  If several words are used to form the name of a method, the first letter of each word should be capitalized.

  Example: def myMethodName()
• Program file name-the name of the program file should exactly match the object name (the new version is not needed, but it is recommended to keep this habit).

  When you save a file, you should save the name of the object it uses (remember that Scala is case sensitive) and append “.scala” to the file extension. (if the file name and object name do not match, the program will not compile.)

  Example: suppose “HelloWorld” is the name of the object. Then the file should be saved as’ HelloWorld.scala’

• def main(args: Array[String]) -Scala program from main() method, which is the mandatory entry part of each Scala program.

8.4.4. Identifier #

Scala can use two forms of markers, characters, numbers and symbols.

Character numbers begin with letters or underscores, followed by letters or numbers, and the symbol “$” is also regarded as a letter in Scala. However, identifiers starting with “$” are used as reserved markers generated by the Scala compiler, and applications should avoid using identifiers that start with “$” to avoid conflicts.

The naming convention of Scala is similar to that of Java, with the first character in lowercase, such as toString . The first character of the class name is still capitalized. You should also avoid using flags that end with an underscore to avoid conflicts. Symbol markers contain one or more symbols, such as +,:,? Wait, for example:

+ ++ ::: < ?> :-> 

Escaped markers are used when implemented internally in Scala, such as :-> use $colon$minus$greater to represent this symbol. So if you need to access the:-> method in your Java code, you need to use the internalname of Scala $colon$minus$greater .

A mixed character consists of a character numeric marker followed by one or more symbols, such as unary_+ is the name of the internal implementation of the + method by Scala. The literal marker is a string defined with “, such as x yield .

You can use any valid Scala marker between `" , which Scala interprets as a Scala marker, a typical use of Thread of yield method, you cannot use it in Scala Thread.yield() It’s because yield for keywords in Scala, you must use the Thread.`yield`() to use this method.

8.4.5. Scala keyword #

The following table lists scala keep the keyword, we cannot use the following keyword as variable:

Object HelloWorld{ /*This is a Scala program *This is a line of comments *This demonstrates multi line comments */ Def main (args: Array [String]){ //Output Hello World //This is a single line comment Println ("Hello, world!") } } 

val s = "Novice Tutorial"; println(s) 

package com.runoob class HelloWorld 

package com.runoob { class HelloWorld } 

Import java. awt. Color//Import Color Import java. awt. _// Introduce all members within the package Def handler (evt: event. ActionEvent) {//java. awt. event. ActionEvent ...//Because of the introduction of java. awt, the previous section can be omitted } 

import java.awt.{Color, Font} // Rename Members import java.util.{HashMap => JavaHashMap} // Hide Members import java.util.{HashMap => _, _} // All members of the util package were introduced, but HashMap was hidden