Базовые концепции Scala
0. ФП и ООП
trait RestClient {
val serviceHost: String
}
class RestClientImpl extends RestClient {
override val serviceHost: String = "192.168.1.1"
}
responseResult.map(result => println(result))
def getResponse(sortFromString: String => ColumnSorting[sortType])
I. Выражения (expressions)
25 + 15
println(25) // 25
println(25 + 15) // 40
println("Hello!") // Hello!
println("Hello," + " world!") // Hello, world!
val x = 1 + 1
println(x) // 2
x = 3 // не компилируется
val y: Int = 41 - 1
var x = 1 + 1
x = 3 // компилируется
II. Функции (functions) и методы (methods)
(x: Int) => x + 1 // анонимная функция
val add = (x: Int, y: Int) => x + y
println(add(1, 2)) // 3
val getTheAnswer = () => 42
println(getTheAnswer()) // 42
def doubleSum(x: Int, y: Int): Int = {
val z = x + y
z * 2
}
println(doubleSum(1, 2)) // 6
def sum(x: Int, y: Int = 11): Int = x + y
println(sum(4)) // out: 15
println(sum(2, 3)) // out: 5
def fourWords(w0: String = "zero",
w1: String = "one",
w2: String = "two",
w3: String = "three"): Unit =
println(s"$w0 $w1 $w2 $w3")
fourWords(w3 = "3", w1 = "1") // out: zero 1 two 3
III. Условное выражение (if expression)
if (a == b) doSomething()
if (trueOrFalse) {
doSomething()
} else if (a != b) {
doSomethingElse()
} else {
doAnotherThing()
}
val minValue = if (a < b) a else b
IV. Циклы (for loops)
val strings = Seq("A", "B")
val numbers = Seq(1, 2, 3)
for (str <- strings) print(s"$str; ") // out: A; B;
for (num <- numbers) print(s"$num; ") // out: 1; 2; 3;
val cars = Seq("Mercedes", "BMW", "Cadillac")
cars.foreach(println) // out: Mercedes BMW Cadillac
// car => println(car)
for (i <- 1 to 5) print(s"$i; ") // out: 1; 2; 3; 4; 5;
for (i <- 1 until 5) print(s"$i; ") // out: 1; 2; 3; 4;
val ingredients = Map(
"sugar" -> 30,
"salt" -> 5,
"pepper" -> 10
)
for ((title, amount) <- ingredients)
println(s"ing $title: ${amount}g") // out: ing sugar: 30g ing salt: 5g ing pepper: 10g
for { i <- 1 to 5
if (i % 2 == 0)
} print(s"i; ") // out: 2; 4;
for { i <- 1 to 5
if (i % 2 == 0)
if (i > 2)
} print(s"$i; ") // out: 4;
// for (enumerators) yield e
val strings = List("A", "B")
val res =
for { i <- 1 to 5
if (i % 2) == 0
str <- strings
} yield s"$str$i; "
res.foreach(print) // out: A2; B2; A4; B4;
V. Циклы (while/do-while)
var i = 0
while (i < 5) {
print(s"$i; ")
i += 1
} // out: 0; 1; 2; 3; 4;
var j = 2
do {
print(s"$j; ")
j -= 1
} while (j > 0) // out: 2; 1;
val res =
while (i < 5) {
someFunction(i)
i += 1
}
print(res) // out: ()
VI. Функции и методы - продолжение
def getNumbers(): Seq[Int] = Seq(11, 22)
def oddOrEven(generator: () => Seq[Int], index: Int): String => String = {
def sayOdd(str: String) = s"$str is odd"
def sayEven(str: String) = s"$str is even"
val numbers = generator()
val num = numbers(index)
if (num % 2 == 0) sayEven else sayOdd
}
println(oddOrEven(getNumbers, 0)("That number")) // out: That number is odd
println(oddOrEven(getNumbers, 1)("And that")) // out: And that is even
def addThenMultiply(x: Int, y: Int)(multiplier: Int): Int = {
val sum = x + y
sum * multiplier
}
println(addThenMultiply(1, 2)(3)) // 9
def updateOrder(newOrder: Order)(implicit ctx: Context): Unit
def callByValue(i: Int): Unit = {
println(s"i => $i")
println(s"ii => $i")
}
var someInt = 2
callByValue ({
someInt += 1
val x = someInt * someInt
x
}) // out: i => 9 ii => 9
def callByName(i: => Int) = {
println(s"i => $i")
println(s"ii => $i")
}
var someInt = 2
callByName ({
someInt += 1
val x = someInt * someInt
x
}) // out: i => 9 ii => 16
VII. Операторы
+ - * / % // арифметические операторы
== != > < >= // операторы сравнения
&& || ! // логические операторы
& | ^ ~ << >> >>> // битовые операторы
= += -= *= /= %= <<= >>= &= ^= |= // операторы присвоения
() [] , ; // прочие
val sum = 1 + 2.+(3)
print(sum) // out: 6
val mult = 3.*(2) * 2
print(mult) // out: 12
case class Vector2D(x: Double, y: Double) {
def * (vec2D: Vector2D) = x * vec2D.x + y * vec2D.y // скалярное произведение
}
val v = Vector2D(1.0, 1.0)
val mult = Vector2D(-2.0, 3.0) * v
println(mult) // out: 1.0
VIII. Базовые типы
val s1: Short = 127
val s2: Short = 255
println(s1.toByte) // out: 127
println(s2.toByte) // out: -1
val hex = 0x7f // hex integer
val l = 1000L // l: Long
val f = 3.14F // f: Float
val ch = 'A' // ch: Char
val str = "true" // str: String
IX. Коллекции (введение)
val tup0 = Tuple2(0, "Zero")
val tup1 = Tuple3(1.0F, 1, "One")
val tup = (2.0F, 2, "Two", tup0, tup1) // tup: Tuple5(...)
println(tup._2) // out: 2
val (num, str) = tup0
println(num) // out: 0
println(str) // out: Zero
val users = List(("Mike", 19), ("Joe", 21))
for ((name, age) <- users) {
println(s"$name is $age years old")
}
users.foreach {
case ("Mike", age) => println(s"Mike is $age years old")
case _ => println("unknown user")
}
val listInt = List(1, 2, 3)
val listStr: List[String] = List("One", "Two", "Three")
val listInt2 = 0 +: listInt // элемент в начало (prepend)
val listInt3 = listInt :+ 4 // элемент в конец (append)
val list4 = listInt2 ++ listInt3 // объединение
for (el <- listStr) print(s"$el; ") // out: One; Two; Three;
for (i <- 1 to 2) print(s"${listInt(i)}; ") // out: 2; 3;
listInt(3) // java.lang.IndexOutOfBoundsException
val diameters = Map(
"Mercury" -> 4878,
("Mars", 6779),
"Earth" -> 12742
)
val moreDiameters = Map("Pluto" -> 2302) ++ diameters
for (d <- diameters) print(s"$d; ") // out: (Mercury,4878); (Mars,6779); (Earth,12742);
println(diameters("Mars") // out: 6779
diameters("Sun") // java.util.NoSuchElementException
val listInt = List(1, 2, 3)
val listDoubleInt = listInt.map(x => x * 2) // List(2, 4, 6)
val filteredInt = listDoubleInt.filter(x => x > 5) // List(6)
val listStr: List[String] = List("One", "Two", "Three")
listStr.foreach(println) // out: One Two Three
listStr.reduce((x, y) => s"$x AND $y") // "One AND Two AND Three"
val diameters = Map(
"Mercury" -> 4878,
"Mars" -> 6779,
"Earth" -> 12742
)
diameters.toSeq // Seq[(String, Int)]((Mercury,4878), (Mars,6779), (Earth,12742))
import scala.collection.mutable.ListBuffer
val mutableList = ListBuffer.empty[Int]
mutableList += 1
mutableList ++= List(2, 3)
mutableList.foreach(println) // out: 1 2 3
import scala.collection.mutable.Map
val diameters = Map(
"Mars" -> 6779,
"Earth" -> 12742
)
diameters += "Uranus" -> 51118
diameters("Mars") = -100
diameters ++= Map("A-C" -> diameters("Earth"))
diameters -= "Earth"
println(diameters) // out: Map(A-C -> 12742, Uranus -> 51118, Mars -> -100)