Introduction to Scala

1 .Introduction to Scala https://gitter.im/ScalaTaiwan/ScalaTaiwan Speaker - Jimin Hsieh - https://tw.linkedin.com/in/jiminhsieh 
 TA - Pishen Tsai - https://github.com/pishen TA - Vito Jeng - vito@is-land.com.tw TA - Mark Yang - youngce0918@gmail.com Hackpad - https://goo.gl/SIfDk7 

2 . Agenda ❖ Why Scala? ❖ Scala concept ❖ Program with Scala ❖ Imperative ❖ Object-Oriented ❖ Functional ❖ Collections ❖ Summary of Scala ❖ Further Reading & Reference ❖ Special Thanks 

3 .Why Scala? 

4 . Why Scala? “I can honestly say if someone had shown me the Programming in Scala book by Martin Odersky, Lex Spoon & Bill Venners back in 2003 I'd probably have never created Groovy.” James Strachan, creator of Groovy Introduction to Scala, Aleksandar Prokopec 

5 . Scala concept ❖ Everything is an object. ❖ Not everything is an object in Java. ❖ There is primitive type in Java. ❖ int, float, boolean, char…etc ❖ Scala is an object-oriented language in pure form: every value is an object and every operation is a method call. ❖ Numeric types and Function are object too. ❖ “+”, “-”, “*”, “/” are methods too. 

6 .Scala Class Hierarchy 

7 . Scala concept ❖ Everything is expression. ❖ Expression - an instruction to execute something that will return a value. from Wiki ❖ You can also say that an expression evaluates to a result or results in a value. ❖ You will hear evaluation from some of Scala geeks, it means the same thing. 

8 . Scala concept ❖ Advanced type system ❖ static ❖ strong ❖ inferred ❖ structural 

9 . Scala concept ❖ Avoid to use null. ❖ Less error prone. ❖ NullPointerException ❖ You don’t need to use Null Object pattern. 

10 . Program with Scala(Main) object Demo1 {
 val todayEvent = "JCConf"
 val workshop = "Introduction to Scala"
 lazy val fun = (0 to 4).map(x => "fun").mkString(" ")
 
 def main(args: Array[String]): Unit = {
 Object with main method. println("Hello everybody!")
 print("Welcome to " + todayEvent + "!\n")
 println("I hope you can enjoy this workshop - "
 + workshop + ". :P")
 print("Scala is so much " + fun + "!")
 }
 } Demo1 

11 . Program with Scala(App) Object with App trait. object Demo2 extends App {
 val todayEvent = "JCConf"
 val workshop = "Introduction to Scala"
 lazy val fun =
 (0 to 4).map(x => "fun").mkString(" ")
 
 println("Hello everybody!")
 print("Welcome to " + todayEvent + "!\n")
 println("I hope you can enjoy this workshop - "
 + workshop + ". :P")
 print("Scala is so much " + fun + "!")
 } Demo2 

12 . Program with Scala(REPL) ❖ REPL - Read-Evaluate-Print Loop 

13 . Program with Scala(REPL) ❖ $ scala -Dscala.color 

14 . Program with Scala(Worksheet) ❖ Work with worksheet. ❖ IntelliJ ❖ https://www.jetbrains.com/help/idea/2016.2/ working-with-scala-worksheet.html ❖ Scala IDE or Eclipse with Scala plugin ❖ https://www.youtube.com/watch?v=Forl4hpg7kA 

15 . Imperative ❖ var, val, semicolons ❖ If expressions ❖ def ❖ Block expressions ❖ While-Loop ❖ For-Loop ❖ Nested Function ❖ Recursion vs Tail-recursion ❖ Concept of Pattern Matching ❖ Pattern Matching v1 

16 . var vs. val ❖ var - variable ❖ val - value ❖ Something that able or ❖ A value is an expression likely to change or be which cannot be changed. Not always evaluated any further. the same. Merriam- Wiki Webster ❖ Opposite to var, val cannot be changed. ❖ It’s similar to final in Java. 

17 . Expression with semicolon? val x = 5566
 val y = 87
 val java = "Java"; val scala = "scala" If you have multiple expressions in one line,
 you will need semicolon(;).
 Otherwise you don’t need it. Demo01 

18 . If expressions ❖ If has return value.(expression) ❖ Scala have no ternary operator(?:). // Java version
 final int value = -1;
 final boolean negative = value < 0 ? true : false; // Scala version
 val value = 0
 val negative = if (value < 0) true else false Everything is an expression. Demo02 

19 . def “def” starts a function definition result type of function function name parameter equals sign def max(x: Int, y: Int): Int = {
 if (x > y)
 x
 else
 function body in curly braces y
 } Programming in Scala, 3ed by Martin Odersky, Lex Spoon, and Bill Venners Demo03 

20 . def def max(x: Int, y: Int): Int = {
 if (x > y)
 return x
 else
 return y
 } Demo04 

21 . def def max(x: Int, y: Int) = {
 if (x > y)
 x
 No function’s result type else
 y
 } Demo05 

22 . def def max(x: Int, y: Int) =
 if (x > y)
 x
 else
 No curly brackets y Demo06 

23 . Summary of def ❖ You don’t need return. ❖ Last expression of block will be the return value. ❖ You don’t need return type in method definition. ❖ Scalac will know your return type in most case. ❖ It’s a good habit to have return type, when your API is a public interface. ❖ You don’t need curly bracket. ❖ If you have multiple lines of code, using curly bracket({}) is a good habit. 

24 . Block expressions(curly brackets) val n = 5
 val factorial = {
 var result = 1
 for (i <- 1 to n)
 result = result * i
 result
 } Last expression(result) in block will be the return value, then it will assign to factorial. Demo07 

25 . While-Loop var n = 10
 var sum = 0
 
 while (n > 0) {
 sum = sum + 1
 n = n - 1
 } Demo08 

26 . For-Loop var sum = 0
 for (i <- 1 to 10) {
 sum += 1
 }
 println(sum) Demo09 

27 . For-Loop for (i <- 0 until 10) {
 println(i)
 } Demo10 

28 . For-Loop val n = 5
 for {i <- 0 to n
 j <- 0 to n} {
 print("*")
 With curly bracket - “{}”, 
 you can use newlines without semicolon - “;”. if (j == n)
 println("")
 } Demo11 

29 . Exercise of For-Loop ❖ Print out something like below.