Programming Kotlin Applications. Бретт Мак-Лахлин

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      NOTE If you're wondering how Kotlin actually knows what type is allowed for a variable, keep reading. Much more on that shortly.

KOTLIN HAS A LARGE NUMBER OF TYPES

      Like any programming language, Kotlin supports lots of basic data types. You can define integers ( Int), sequences of letters ( String), decimal numbers ( Float), and a lot more. Let's take a blazing-fast run through the basic types and then start putting them to use.

      Numbers in Kotlin

Kotlin gives you four options for integers, largely varying based on range. These are shown in Table 2.1.

TABLE 2.1: Kotlin Types for Integers (Nondecimal Numbers)

TYPE	SIZE (BITS)	MINIMUM VALUE	MAXIMUM VALUE
Byte	8	–128	127
Short	16	–32,678	32,767
Int	32	–2,147,483,648 (–231)	2,147,483,647 (231 – 1)
Long	64	–9,223,372,036,854,775,808 (–263)	9,223,372,036,854,775,807 (263 – 1)

      Kotlin will largely take care of figuring out which type to use when you don't declare that type explicitly. In that case, it's going to look at the value you're assigning the variable, and make some assumptions. This is a pretty important concept called type inference, and it's something we're going to talk about in a lot more detail in Chapter 6.

      If you create a variable and assign it a number that fits into Int, then Int will be used. If the number is outside the range of Int, the variable will be created as a Long :

      val someInt = 20 val tooBig = 4532145678

      So here, someInt will be an Int. tooBig is too big to fit into an Int so it will be a Long. You can also force a variable to be a Long by adding a capital L to the value:

      val makeItLong = 42L

Kotlin gives you a couple of options for decimals, as well: two, again, based on precision and size. Those are listed in Table 2.2.

TABLE 2.2: Kotlin Types for Decimal Numbers

TYPE	SIZE (BITS)	SIGNIFICANT BITS	EXPONENT BITS	DECIMAL DIGITS
Float	32	24	8	6–7
Double	64	53	11	15–16

      Assignment here works a bit unexpectedly. Decimal variables will be Double unless you tell Kotlin to use Float by using the f or F suffix:

      val g = 9.8 val theyAllFloat = 9.8F

      Letters and Things

      If you want to represent a single character—including special characters like backslash or a carriage return—you use the Char type:

      val joker = 'j'

      A character should be enclosed in a set of single quotes. You can also enclose special characters in quotes and precede the character code with a backslash. For instance, tab is \t, a line feed is \n, and a backslash is itself \\ :

      val special = '\n'

      NOTE Backslash is weird because it is itself an escape character. To get an actual backslash, you use the escape character ( \ ) and then another backslash ( \ ), which gets you \\ .

For sequences of characters, you likely want a String. You can create a string with text enclosed in double quotes:

      val letters = "abcde"

      Simple enough! But note that a single letter in double quotes is a String, while a single letter in single quotes is a Char :

      val letter = "a" val notStringy = 'a'

      Truth or Fiction

      For true or false values, you can use a Boolean. You can assign to a Boolean either true or false:

      val truthful = true val notTrue = false

      However, you cannot use 0 or 1 as you can in some languages. A 0 is an Int (or a Long, or even a Float):

      val notBoolean = 0 val zeroInt = 0 val zeroLong = 0L val zeroFloat = 0F

      A 0 is never a Boolean, though.

      Types Aren't Interchangeable (Part 1)

      Most of these types are likely unsurprising. They're typical for most languages. What will surprise you a bit is how far Kotlin will go to ensure you don't get your types wrong. Remember, Kotlin is strongly typed, and the language takes that pretty seriously.

To see this in action, let's add some basic information to the Person class. Listing СКАЧАТЬ