Values are Objects

In Scala all values are objects. An object is a grouping of data and operations on that data. For example, 2 is an object. The data is the integer 2, and the operations on that data are familiar operations like +, -, and so on. We call operations of an object the object's methods.

Method Calls

We interact with objects by calling or invoking methods. For example, we can get the uppercase version of a String by calling its toUpperCase method.

"Titan!".toUpperCase
// res0: String = "TITAN!"

Some methods accept parameters or arguments, which control how the method works. The take method, for example, takes characters from a String. We must pass a parameter to take to specify how many characters we want.

"Gilgamesh went abroad in the world".take(3)
// res1: String = "Gil"
"Gilgamesh went abroad in the world".take(9)
// res2: String = "Gilgamesh"

A method call is an expression, and thus evaluates to an object. This means we can chain method calls together to make more complex programs:

"Titan!".toUpperCase.toLowerCase
// res3: String = "titan!"

anExpression.methodName(param1, ...)

anExpression.methodName

Operators

We have said that all values are objects, and we call methods with the syntax object.methodName(parameter). How then do we explain expressions like 1 + 2?

In Scala, and expression written a.b(c) can be written a b c. So these are equivalent:

1 + 2
// res4: Int = 3
1.+(2)
// res5: Int = 3

This first way of calling a method is known as operator style.