1.2 Scala Basics

Type definitions Scala s: String i: Int Java String s int i / Integer i

Variables Scala: val s = “Hello World” var i = 1 private var j = 3 Java: public final String s = “Hello World”; public int i = 1; private int j = 3;

Methods Scala: def add(x: Int, y: Int): Int = { x + y } def add(x: Int, y: Int) = x + y def doSomething(text: String) { } Java: public int add(int x, int y) { return x + y; } public void doSometing(String text) { }

Methods (2) Scala: myObject.myMethod(1) myObject myMethod(1) myObject myMethod 1 myObject.myOtherMethod(1, 2) myObject myOtherMethod(1, 2) myObject.myMutatingMethod() myObject.myMutatingMethod myObject myMutatingMethod Java: myObject.myMethod(1); myObject.myOtherMethod(1, 2); myObject.myMutatingMethod()

Methods (3) Scala: override def toString = ... Java: @Override public String toString() {...}

Classes and constructors Scala: class Person(val name: String) Java: public class Person { private final String name; public Person(String name) { this.name = name; } public String getName() { return name; } }

Traits (= Interface + Mixin) Scala: trait Shape { def area: Double } class Circle extends Object with Shape Java: interface Shape { public double area(); } public class Circle extends Object implements Shape

No “static” in Scala Scala: object PersonUtil { val AgeLimit = 18 def countPersons(persons: List[Person]) = ... } Java: public class PersonUtil { public static final int AGE_LIMIT = 18; public static int countPersons(List<Person> persons) { ... } }

if-then-else Scala: if (foo) { ... } else if (bar) { ... } else { ... } Java: if (foo) { ... } else if (bar) { ... } else { ... }

For-loops Scala: for (i <- 0 to 3) { ... } for (s <- args) println(s) Java: for (int i = 0; i < 4; i++) { ... } for (String s : args) { System.out.println(s); }

While-loops Scala: while (true) { ... } Java: while (true) { ... }

Exceptions Scala: throw new Exception(“...”) try { } catch { case e: IOException => ... } finally { } Java: throw new Exception(“...”) try { } catch (IOException e) { ... } finally { }

Varargs def foo(values: String*){ } foo("bar", "baz") val arr = Array("bar", "baz") foo(arr: _*) public void foo(String... values){ } foo("bar", "baz"); String[] arr = new String[]{"bar", "baz"} foo(arr);

(Almost) everything is an expression val res = if (foo) x else y val res = for (i <- 1 to 10) yield i // List(1, ..., 10) val res = try { x } catch { ...; y } finally { } // x eller y

Collections – List Scala: val numbers = List(1, 2, 3) val numbers = 1 :: 2 :: 3 :: Nil numbers(0) => 1 Java: List<Integer> numbers = new ArrayList<Integer>(); numbers.add(1); numbers.add(2); numbers.add(3); numbers.get(0); => 1

Collections – Map Scala: var m = Map(1 -> “apple”) m += 2 -> “orange” m(1) => “apple” Java: Map<Int, String> m = new HashMap<Int, String>(); m.put(1, “apple”); m.put(2, “orange”); m.get(1); => apple

Generics Scala: List[String] Java: List<String>

Tuples Scala: val tuple: Tuple2[Int, String] = (1, “apple”) val quadruple = (2, “orange”, 0.5d, false) Java: Pair<Integer, String> tuple = new Pair<Integer, String>(1, “apple”) ... yeah right... ;-)

Packages Scala: package mypackage ... Java: package mypackage; ...

Imports Scala: import java.util.{List, ArrayList} import java.io._ import java.sql.{Date => SDate} Java: import java.util.List import java.util.ArrayList import java.io.* ???

Nice to know Scala: Console.println(“Hello”) println(“Hello”) val line = Console.readLine() val line = readLine() error(“Bad”) 1 + 1 1 .+(1) 1 == new Object 1 eq new Object """A\sregex""".r Java: System.out.println(“Hello”); BufferedReader r = new BufferedReader(new InputStreamRead(System.in) String line = r.readLine(); throw new RuntimException(“Bad”) new Integer(1).toInt() + new Integer(1).toInt(); new Integer(1).equals(new Object()); new Integer(1) == new Object(); java.util.regex.Pattern.compile(“A\\sregex”);

1.2 Scala Basics

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1.2 Scala Basics