Java and Scala are both modern, powerful languages that offer a range of features for developers, and while they differ in their paradigms (Java being primarily object-oriented and Scala being a hybrid of object-oriented and functional programming), they do share some similarities, especially as both languages have evolved. As an experienced Java developer (from Java 7 to the latest) and also experienced Scala developer I will try to compare the two languages.<\/p>\n\n\n\n
Immutability in Java refers to the design of objects whose state cannot be modified after they are created. Once an immutable object is instantiated, its fields cannot be changed, which provides several advantages, including thread safety, simplicity, and easier debugging. The most well-known immutable class in Java is Java 17<\/strong><\/p>\n\n\n\n Records automatically generate:<\/p>\n\n\n\n However, records provide shallow immutability<\/strong>.<\/p>\n\n\n\n The reference cannot change, but the list can.<\/p>\n\n\n\n Scala 2.13<\/strong><\/p>\n\n\n\n Case classes are immutable by convention.<\/p>\n\n\n\n Fields are Scala 3<\/strong><\/p>\n\n\n\n Same concept, with additional compiler improvements.<\/p>\n\n\n\n Sealed types restrict who may extend a hierarchy.<\/p>\n\n\n\n Java 17<\/strong><\/p>\n\n\n\n Useful for exhaustive pattern matching.<\/p>\n\n\n\n Scala 2.13<\/strong><\/p>\n\n\n\n All subclasses must be in the same source file.<\/p>\n\n\n\n Exactly the same idea.<\/p>\n\n\n\n Scala 3 enums automatically create sealed hierarchies.<\/p>\n\n\n\n Pattern matching allows branching based on structure, not just type.<\/p>\n\n\n\n Switch pattern matching was still a preview feature.<\/p>\n\n\n\n Scala 2.13<\/strong><\/p>\n\n\n\n Can match:<\/p>\n\n\n\n Scala’s pattern matching is far more expressive.<\/p>\n\n\n\n Type inference lets the compiler determine types automatically.<\/p>\n\n\n\n Only local variables.<\/p>\n\n\n\n Inference works for<\/p>\n\n\n\n Scala 3 further improves inference.<\/p>\n\n\n\n Lambdas represent anonymous functions.<\/p>\n\n\n\n Requires functional interfaces.<\/p>\n\n\n\n Functions are true objects.<\/p>\n\n\n\n Collections are central to functional programming.<\/p>\n\n\n\n Uses<\/p>\n\n\n\n Streams are separate from collections.<\/p>\n\n\n\n Everything supports<\/p>\n\n\n\n without converting to streams.<\/p>\n\n\n\n Functional programming emphasizes pure functions, immutable data, and function composition.<\/p>\n\n\n\n Java supports FP, but Scala is designed around it.<\/p>\n\n\n\n Scala libraries:<\/p>\n\n\n\n make purely functional programming practical.<\/p>\n\n\n\n Both represent optional values.<\/p>\n\n\n\n Designed mainly for return types.<\/p>\n\n\n\n Scala<\/strong><\/p>\n\n\n\n Behaves like a collection.<\/p>\n\n\n\n Null references are a common source of runtime errors.<\/p>\n\n\n\n Perfectly legal.<\/p>\n\n\n\n Prefer<\/p>\n\n\n\n instead of null.<\/p>\n\n\n\n With Explicit Nulls<\/p>\n\n\n\n and<\/p>\n\n\n\n are different types.<\/p>\n\n\n\n Much safer.<\/p>\n\n\n\n Exception handling reports errors during execution.<\/p>\n\n\n\n Compiler forces checked exceptions.<\/p>\n\n\n\n Only unchecked exceptions.<\/p>\n\n\n\n Functional libraries usually avoid exceptions entirely by using:<\/p>\n\n\n\n ADTs model complex domains by combining product types (AND) and sum types (OR).<\/p>\n\n\n\n Java<\/strong><\/p>\n\n\n\n Scala<\/strong><\/p>\n\n\n\n Scala 3<\/strong><\/p>\n\n\n\n Scala offers much more concise ADT support.<\/p>\n\n\n\n Higher-order functions either accept functions as parameters or return functions.<\/p>\n\n\n\n Java:<\/p>\n\n\n\n Scala:<\/p>\n\n\n\n Higher-order functions are fundamental in Scala.<\/p>\n\n\n\n Implicits allow values or conversions to be supplied automatically by the compiler.<\/p>\n\n\n\n Scala 2:<\/strong><\/p>\n\n\n\n Scala 3<\/strong> replaces this with clearer syntax:<\/p>\n\n\n\n Java<\/strong> has no comparable language feature.<\/p>\n\n\n\n Extension methods add behavior to existing types without inheritance.<\/p>\n\n\n\n Java uses utility classes:<\/p>\n\n\n\n Scala 2<\/p>\n\n\n\n Scala 3<\/p>\n\n\n\n This is now a first-class language feature.<\/p>\n\n\n\n Value classes wrap existing types without (in many cases) introducing runtime allocation.<\/p>\n\n\n\n Scala 2:<\/p>\n\n\n\n Scala 3 favors opaque types:<\/p>\n\n\n\n These provide type safety with effectively zero runtime overhead.<\/p>\n\n\n\n Java has no direct equivalent in Java 17 (Project Valhalla aims to introduce value objects in a future release).<\/p>\n\n\n\n A language’s type system determines how expressive and safe programs can be.<\/p>\n\n\n\n Java offers:<\/p>\n\n\n\n Scala additionally supports:<\/p>\n\n\n\n Scala’s type system is among the most expressive of mainstream programming languages.<\/p>\n\n\n\n Compilation speed affects developer productivity, especially in large codebases.<\/p>\n\n\n\n The learning curve reflects how quickly developers become productive.<\/p>\n\n\n\n Introduction Java and Scala are both modern, powerful languages that offer a range of features for developers, and while they differ in their paradigms (Java being primarily object-oriented and Scala being a hybrid of object-oriented and functional programming), they do share some similarities, especially as both languages have evolved. As an experienced Java developer (from … Continue reading Java 17 LTS through the eyes of Scala developer<\/span> String<\/code>, but developers can create their own immutable classes.<\/p>\n\n\n\npublic record Person(String name, int age) {}<\/pre>\n\n\n\n\n
record Team(List<String> members) {}<\/pre>\n\n\n\ncase class Person(name: String, age: Int)<\/pre>\n\n\n\n
val p = Person(\"John\", 30)<\/pre>\n\n\n\n
val<\/code> unless explicitly declared var<\/code>.<\/p>\n\n\n\n2. Sealed Types<\/h2>\n\n\n\n
sealed interface Shape\n permits Circle, Rectangle {}<\/pre>\n\n\n\nsealed trait Shape\ncase class Circle(r: Double) extends Shape\ncase class Rectangle(w: Double,h: Double) extends Shape<\/pre>\n\n\n\n
Scala 3<\/h3>\n\n\n\n
3. Pattern Matching<\/h2>\n\n\n\n
Java 17<\/h3>\n\n\n\n
if (obj instanceof String s) {\n System.out.println(s.length());\n}<\/pre>\n\n\n\nshape match {\n case Circle(r) => ...\n case Rectangle(w,h) => ...\n}<\/pre>\n\n\n\n\n
4. Type Inference<\/h2>\n\n\n\n
Java<\/h3>\n\n\n\n
var list = List.of(1,2,3);<\/pre>\n\n\n\n
Scala<\/h3>\n\n\n\n
val list = List(1,2,3)<\/pre>\n\n\n\n
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5. Lambdas<\/h2>\n\n\n\n
Java<\/h3>\n\n\n\n
list.stream()\n .map(x -> x * 2)<\/pre>\n\n\n\n
Scala<\/h3>\n\n\n\n
list.map(_ * 2)<\/pre>\n\n\n\n
6. Collections<\/h2>\n\n\n\n
Java<\/h3>\n\n\n\n
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Scala<\/h3>\n\n\n\n
map\nflatMap\nfilter\ncollect\ngroupBy\npartition\nfold\nreduce\nscan<\/pre>\n\n\n\n
7. Functional Programming<\/h2>\n\n\n\n
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8. Optional vs Option<\/h2>\n\n\n\n
Java<\/h3>\n\n\n\n
Optional<String><\/pre>\n\n\n\n
Option[String]<\/pre>\n\n\n\n
option.map(...)\noption.flatMap(...)\noption.filter(...)<\/pre>\n\n\n\n
9. Null Safety<\/h2>\n\n\n\n
Java<\/h3>\n\n\n\n
String s = null;<\/pre>\n\n\n\n
Scala 2<\/h3>\n\n\n\n
Option[String]<\/pre>\n\n\n\n
Scala 3<\/h3>\n\n\n\n
String<\/pre>\n\n\n\n
String | Null<\/pre>\n\n\n\n
10. Exceptions<\/h2>\n\n\n\n
Java<\/h3>\n\n\n\n
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Scala<\/h3>\n\n\n\n
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Try<\/code><\/li>\n\n\n\nEither<\/code><\/li>\n\n\n\nIO<\/code><\/li>\n\n\n\nZIO<\/code><\/li>\n<\/ul>\n\n\n\n11. Algebraic Data Types (ADT)<\/h2>\n\n\n\n
sealed interface Expr {}\n\nrecord Num(int value) implements Expr {}\nrecord Add(Expr l, Expr r) implements Expr {}<\/pre>\n\n\n\nsealed trait Expr\n\ncase class Num(v:Int) extends Expr\ncase class Add(l:Expr,r:Expr) extends Expr<\/pre>\n\n\n\n
enum Expr:\n case Num(v:Int)\n case Add(l:Expr,r:Expr)<\/pre>\n\n\n\n
12. Higher-Order Functions<\/h2>\n\n\n\n
list.forEach(System.out::println);<\/pre>\n\n\n\n
list.foreach(println)<\/pre>\n\n\n\n
13. Implicits<\/h2>\n\n\n\n
implicit val ec = ExecutionContext.global<\/pre>\n\n\n\n
given ExecutionContext = ExecutionContext.global\n\ndef run(using ExecutionContext)<\/pre>\n\n\n\n
14. Extension Methods<\/h2>\n\n\n\n
Collections.sort(list);<\/pre>\n\n\n\n
implicit class RichString(s: String)<\/pre>\n\n\n\n
extension (s: String)\n def hello = ...<\/pre>\n\n\n\n
15. Value Classes<\/h2>\n\n\n\n
class UserId(val value: Long) extends AnyVal<\/pre>\n\n\n\n
opaque type UserId = Long<\/pre>\n\n\n\n
16. Type System<\/h2>\n\n\n\n
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17. Compilation Speed<\/h2>\n\n\n\n
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18. Learning Curve<\/h2>\n\n\n\n
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given<\/code>\/using<\/code> mechanism, extension methods, enums, and improved error messages reduce much of the accidental complexity while preserving Scala’s expressive power.<\/li>\n<\/ul>\n\n\n\nOverall comparison<\/h2>\n\n\n\n
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