val x: Long = 987654321
val y: Float = x // 9.8765434E8 (note that some precision is lost in this case)
val face: Char = '☺'
val number: Int = face // 9786
class Point(var x: Int, var y: Int) {
override def toString: String =
s"($x, $y)"
}
val point1 = new Point(2, 3)
point1.x // 2
println(point1) // prints (2, 3)
和其他的编程语言不同的是，Scala的类构造器定义在类的签名中：(var x: Int, var y: Int)。 这里我们还重写了AnyRef里面的toString方法。
构造器也可以拥有默认值：
class Point(var x: Int = 0, var y: Int = 0)
val origin = new Point // x and y are both set to 0
val point1 = new Point(1)
println(point1.x) // prints 1
主构造方法中带有val和var的参数是公有的。然而由于val是不可变的，所以不能像下面这样去使用。
class Point(val x: Int, val y: Int)
val point = new Point(1, 2)
point.x = 3 // <-- does not compile
不带val或var的参数是私有的，仅在类中可见。
class Point(x: Int, y: Int)
val point = new Point(1, 2)
point.x // <-- does not compile
class Point {
private var _x = 0
private var _y = 0
private val bound = 100
def x = _x
def x_= (newValue: Int): Unit = {
if (newValue < bound) _x = newValue else printWarning
}
def y = _y
def y_= (newValue: Int): Unit = {
if (newValue < bound) _y = newValue else printWarning
}
private def printWarning = println("WARNING: Out of bounds")
}
object Point {
def main(args: Array[String]): Unit = {
val point1 = new Point
point1.x = 99
point1.y = 101 // prints the warning
}
}
trait Iterator[A] {
def hasNext: Boolean
def next(): A
}
class IntIterator(to: Int) extends Iterator[Int] {
private var current = 0
override def hasNext: Boolean = current < to
override def next(): Int = {
if (hasNext) {
val t = current
current += 1
t
} else 0
}
}
val iterator = new IntIterator(10)
iterator.next() // returns 0
iterator.next() // returns 1
子类型
和java一样，所有需要用到Traits的地方都可以用他的子类型代替。
import scala.collection.mutable.ArrayBuffer
trait Pet {
val name: String
}
class Cat(val name: String) extends Pet
class Dog(val name: String) extends Pet
val dog = new Dog("Harry")
val cat = new Cat("Sally")
val animals = ArrayBuffer.empty[Pet]
animals.append(dog)
animals.append(cat)
animals.foreach(pet => println(pet.name)) // Prints Harry Sally
