Question

When I rename a .scala file via Eclipse the class name itself is not renamed.

Is this expected behaviour? It does not seem to break anything.

I expect it to be renamed, coming from a Java background the filename/class name must equal each other.

Answer 1

correspondence between class name and file name is not required in scala.
You can (and usually do) define multiple types in each scala file.
The compiler will attempt to create a different .class file for each public type with the file name corresponding to the type name, for interoperability with java (for complex or nested types that don’t have a direct correspondence in java, scalac will produce .class files with strange/mangled names…)

A few notes on why this correspondence is not enforced (probably not a complete list, but just to give you an idea):

1. it would be wasteful, given scala’s terseness. case class Foo(foo:String) corresponds to a complete and somewhat sophisticated java class, but having it in its own file seems wasteful…
2. it would decrease code readability. Sometimes you define a hierarchy of case classes that correspond (for instance) to various messages you send to an actor. Having them together underlines their intent.
3. often it would be pointless. A relatively simple definition in scala, like trait Fooer {def foo="foo"} may be translated to various java-like types, that implement the “interface with a default implementation” nature of a trait. This gets worse for nested object/classes/types allowed by scala’s syntax and used in some common scala patterns.
4. there are Scala semantics (sealed traits in particular) that actually require having multiple classes defined in a single file (credit to @DaveGriffith ‘s comment below)