Data Types

In the previous lesson, you learned how to assign a variable. Well, what you didn't know is that when you assigned those variables they were implicitly assigned types as well. If your variable was a string (using quotation marks), then it had the type String. If it was a number, then it probably had the type Int, or Double if the number contained a decimal. Or maybe Long if it was a really big number. There are a lot of number types. Anyways, here is a list of the most basic types in Kotlin.

  • String - Used to store text. We already learned about this one!

  • Char - A character, like 'a' or 'b'. Create one using single quotes '...'.

  • Int - An integer. Used to store numbers of reasonable size.

  • Long - A big integer. No surprises here, a Long is... long. Used to store very large

    numbers.

  • Float - A floating point number. Used to store numbers with decimals that do not need

    much accuracy. To create one, write a number followed by an 'F', like this: 1.5F

  • Double - A more precise floating point number. Used more often than Float because it is, well, double the precision. Create one by adding a decimal after a number, like this: 18. or 8928.0 or 2.82376437

  • Boolean - Possibly the most essential data type there is, a Boolean is either true or

    false. Note that like numbers, true and false do not need quotation marks.

That should be enough to keep us busy, right? So lets look at how we can apply these types to our programs. Here is an example of setting a variable, but rather than letting Kotlin imply the type, we tell it exactly what type we want it to be.

val sertIsAwesome: Boolean = true

There's some new syntax here that we need to cover. Notice that after the variable's name, we have a colon : followed by the type of the variable, Boolean. After that, we have the = and then the value like usual. Here are some more examples:

val firstLetterOfSert: Char = 'S'
val pi: Float = 3.14F
val sertIsNotCool: Boolean = false

Note that in any of these examples, we could have just as easily declared the variable without a type because Kotlin is smart enough to interpret the type for us if we don't specify one. The purpose of types is to make sure certain values can only be used for certain things. For instance, it would not make much sense to try to add 3 to false

Your Turn

  1. Open src/main/kotlin/part1/DataTypes.kt.

  2. Explicitly make the variable name a String, and assign it to your name.

  3. Use println(...) to print it's value to the console. Run the program.

  4. After the name variable inside println(...), type is String. What do you think will

    happen? Run the program.

  5. This time, put is Boolean after the variable, and run it again. What was the result?

Wasn't that neat? The console should have printed true for name is String and false for name is Boolean. The is keyword, as we just observed, can be used to check whether or not a variable is a certain type. The result of using an is statement is true or false, making it a... Boolean! Every time something has a value in Kotlin, it has a data type. Remember, a data type is just a way for the language to know what a variable can and cannot be used for, so try not to think about it too much.

PreviousVariablesNextOperators

Last updated