Java Vs Scala

Reference:

• Why Scala
• Scala for the intrigued

Object Orientation

Java is not pure Object Oriented: It has Primitive Types and Reference Types. Eg. System.out.println(1.toString) would fail.

In Scala, everything is a Reference Type. So println(1.toString) works. Scala uses the correct type at compile time when generating bytecode i.e. in this case it either generates an Int object or a Java int in bytecode.

Final

In Java you have to declare specific variables that you do not want to change as final.

In Scala, by default variables defined using val or def are final. You can use var to define variables that can change.

Singletons and Static/Class variables

In Java you have to implement Singleton manually, also to keep track of certain things (eg. instance count, etc) you have to use static variables or methods.

In Scala, a singleton can be defined by just writing a regular class with the keyword object instead of class. Also if you have a class of which you want to keep track of certain things (eg. instance count, etc), then just declare an object with the same name as that of the class. In this case, the object becomes the "companion object" of the class. All definitions inside this object will be static by default i.e. these will be Class Variables.

class Car {
}
object Car {
    def someMethod = { ... }
    val someString = "Hello"
}
// usage:
def c1 = new Car
def c2 = new Car
println(Car.someString)

Classname Convention

Java requires classname and filename to be the same.

Scala does not have this requirement. Only requirement is a class and its companion object be defined in the same file.