This document summarizes key similarities and differences between Scala and Java types, variables, methods, classes, collections, control structures, and other language features. Some of the main points covered include: - Type definitions, variables, and methods are defined similarly but with different syntax in Scala vs Java - Classes and traits in Scala are like classes and interfaces in Java - Scala avoids static methods and instead uses singleton objects - Control structures like if/else, for loops, and exceptions work similarly - Scala supports features like tuples, pattern matching, and expression-oriented programming that have no direct equivalent in Java

1. Scala basics

2. ;

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

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

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

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

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

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

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

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

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

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

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

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

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

16. (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 or y

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

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

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

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

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

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

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