The document discusses pattern matching in Scala, including using match expressions to check for different cases and extract values, using case classes that can be used in pattern matching, and using the Option type to handle potential null values instead of NullPointerExceptions. It also includes examples of using regular expressions in pattern matching and tasks for a code exercise on pattern matching.

1. Pattern matching

2. myObject match {
case 1 => println("First was hit")
case 2 => println("Second was Hit")
case _ => println("Unknown")
}

3. myObject match {
case i: Int => println("Found an int")
case s: String => println("Found a String")
case _ => println("Unknown")
}

4. myObject match {
case i: Int => println("Found an int")
case s: String => println("Found an String")
case other => println("Unknown " + other)
}

5. myObject match {
case i: Int if i == 1 => println("Found an int")
case s: String => println("Found a String")
case other => println("Unknown " + other)
}

6. val res = myObject match {
case i: Int if i == 1 => "Found an int"
case s: String => "Found a String"
case other => "Unknown " + other
}

7. val res = myObject match {
case (first, second) => second
case (first, second, third) => third
}

8. val mathedElement = list match {
case List(firstElement, lastElement) => firstElement
case List(firstElement, _ *) => firstElement
case _ => "failed"
}

9. def length(list: List[_]): Int =
list match {
case Nil => 0
case head :: tail => 1 + length(tail)
}

10. public static Integer getSecondOr0(List<Integer> list) {
if (list != null && list.size() >= 2) {
return list.get(1);
} else {
return 0;
}
}
def second_or_0(list:List[Int]) = list match {
case List(_, x, _*) => x
case _ => 0
}

11. Case classes
Class types that can be used in pattern matching
Generated into your class:
equals
hashCode
toString
getters (and optionally setters)
++

12. abstract class Person(name: String)
case class Man(name: String) extends Person(name)
case class Woman(name: String, children: List[Person])
extends Person(name)

13. p match {
case Man(name) => println("Man with name " + name)
case Woman(name, children) => println("Woman with name "
+ name + " and with " +
children.size + " children")
}

14. val regex = """(d+)(w+)""".r
val myString = ...
val res: String = myString match {
case regex(digits, word) => digits
case _ => "None"
}

15. val regex = """(d+)(w+)""".r
val myString = ...
val res: Option[String] = myString match {
case regex(digit, word) => Some(digit)
case _ => None
}

16. The Option type, never again
NullPointerException
Option has two possible values
Some(value)
None
val someOption: Option[String] = Some("value")
val noOption: Option[String] = None

17. def getValue(s: Any): Option[String]
getValue(object) match {
case Some(value) => println(value)
case None => println("Nothing")
}
val result = getValue(object).getOrElse("Nothing")

18. Tasks (30 min)
Open the 'pattern-matching' project
Tests in package scalaexamples.patternmatching
Add @Test to one and one method
Follow instructions in the code
Make the tests pass