class Greeter(prefix: String, suffix: String) {
def greet(name: String): Unit =
println(prefix + name + suffix)
}
类里面我们定义了一个方法greet,它的返回值是Unit,可以看成是java中的void。
你可以使用new关键词来创建类的实例:
val greeter = new Greeter("Hello, ", "!")
greeter.greet("Scala developer") // Hello, Scala developer!
case类
scala中有一种专门用来做比较的类叫做case class:
case class Point(x: Int, y: Int)
case class可以不用new来实例化:
val point = Point(1, 2)
val anotherPoint = Point(1, 2)
val yetAnotherPoint = Point(2, 2)
他们的值可以做比较:
if (point == anotherPoint) {
println(point + " and " + anotherPoint + " are the same.")
} else {
println(point + " and " + anotherPoint + " are different.")
} // Point(1,2) and Point(1,2) are the same.
if (point == yetAnotherPoint) {
println(point + " and " + yetAnotherPoint + " are the same.")
} else {
println(point + " and " + yetAnotherPoint + " are different.")
} // Point(1,2) and Point(2,2) are different.
对象
对象使用object来定义的,对象可以看成是它自己类的单例。
object IdFactory {
private var counter = 0
def create(): Int = {
counter += 1
counter
}
}
你可以通过引用它的名字来访问一个对象。
val newId: Int = IdFactory.create()
println(newId) // 1
val newerId: Int = IdFactory.create()
println(newerId) // 2
trait
trait是包含某些字段和方法的类型。使用trait关键字来定义,它和java的接口很类似:
trait Greeter {
def greet(name: String): Unit
}
trait可以有默认的实现:
trait Greeter {
def greet(name: String): Unit =
println("Hello, " + name + "!")
}
trait可以使用extends来继承,并使用override来覆盖默认的实现:
class DefaultGreeter extends Greeter
class CustomizableGreeter(prefix: String, postfix: String) extends Greeter {
override def greet(name: String): Unit = {
println(prefix + name + postfix)
}
}
val greeter = new DefaultGreeter()
greeter.greet("Scala developer") // Hello, Scala developer!
val customGreeter = new CustomizableGreeter("How are you, ", "?")
customGreeter.greet("Scala developer") // How are you, Scala developer?
main方法
和java一样,scala的main方法也是程序运行的入口。Scala 中的 main 方法是 def main(args: Array[String]),而且必须定义在 object 中。如下所示:
object Main {
def main(args: Array[String]): Unit =
println("Hello, World!")
}