Why is String different than Int,Boolean,Byte... in scala?
scala
Solution
First, 'well its not even java.lang.String' statement is not quite correct. Plain `String` name comes from type alias defined in `Predef` object:
type String = java.lang.String
and insides of `Predef` are imported in every Scala source, hence you use `String` instead of full `java.lang.String`, but in fact they are the same.
`java.lang.String` is very special class treated by JVM in special way. As @pagoda_5b said, it is declared as `final`, it is not possible to extend it (and this is good in fact), so Scala library provides a wrapper (`RichString`) with additional operations and an implicit conversion `String -> RichString` available by default.
However, there is slightly different situation with `Integer`, `Character`, `Boolean` etc. You see, even though `String` is treated specially by JVM, it still a plain class whose instances are plain objects. Semantically it is not different from, say, `List` class. There is another situation with primitive types. Java `int`, `char`, `boolean` types are not classes, and values of these types are not objects. But Scala is fully object-oriented language, there are no primitive types. It would be possible to use `java.lang.{Integer,Boolean,...}` everywhere where you need corresponding types, but this would be awfully inefficient because of boxing. Because of this Scala needed a way to present Java primitive types in object-oriented setting, and so `scala.{Int,Boolean,...}` classes were introduced. These types are treated specially via Scala compiler - scalac generates code working with primitives when it encounters one of these classes. They also extend `AnyVal` class, which prevents you from using `null` as a value for these types. This approach solves the problem with efficiency, leaves `java.lang.{Integer,Boolean,...}` classes available where you really need boxing, and also provides elegant way to use primitives of another host system (e.g. .NET runtime).
Problem
Because I know a little bit Java I was trying to use in every Scala Code some Java types like `java.lang.Integer`, `java.lang.Character`, `java.lang.Boolean` ... and so on. Now people told me "No! For everything in Scala there is an own type, the Java stuff will work - but you should always prefer the Scala types and objects". Ok now I see, there is everything in Scala that is in Java. Not sure why it is better to use for example Scala Boolean instead of Java Boolean, but fine. If I look at the types I see `scala.Boolean`, `scala.Int`, `scala.Byte` ... and then I look at String but its not `scala.String`, (well its not even `java.lang.String` confuse) its just a String. But I thought I should use everything that comes direct from scala. Maybe I do not understand scala correctly, could somebody explain it please?