在Scala的溪流

Scala | 流 (Scala | Streams)

Stream in Scala is a type of lazy val. It is a lazy val whose elements are evaluated only when they are used in the program. Lazy initialization is a feature of Scala that increases the performance of the program.

Scala中的Stream是一种惰性val 。这是一个懒惰的val，其元素仅在程序中使用时才被评估。延迟初始化是Scala的一项功能，可以提高程序的性能。

Syntax:

句法：

    val str = 1 #:: 2 #:: 3 #:: Stream.empty

Elements of a stream are created using #:: operator using Stream.empty at the end of initialization.

在初始化结束时，使用＃::运算符使用Stream.empty创建流的元素。

Program to show the creation of a stream

显示流创建的程序

object myObject 
{ 
def main(args:Array[String]) 
{ 
val myStream =  2 #:: 4 #:: 6 #:: Stream.empty; 
println("New Stream created...")
println(myStream)
} 
}

Output

输出量

New Stream created...
Stream(2, <not computed>)

Creating stream using stream.cons

使用stream.cons创建流

You can create a stream using stream.cons. It will create an immutable stream and needs an import statement Scala.collection.immutable.Stream.cons.

您可以使用stream.cons创建流。它将创建一个不可变的流，并且需要一个导入语句Scala.collection.immutable.Stream.cons 。

import scala.collection.immutable.Stream.cons 
object myObject 
{ 
def main(args:Array[String]) 
{ 
val myStream: Stream[Int] = cons(2, cons(4, cons(6, Stream.empty)))
println("New Stream created...")
println(myStream)
} 
}

Output

输出量

New Stream created...
Stream(2, <not computed>)

Accessing elements of the stream

访问流中的元素

In streams, take method is used to take/access elements.

在流中， take方法用于获取/访问元素。

Program to access elements using take method

程序使用take方法访问元素

import scala.collection.immutable.Stream.cons
object myObject 
{ 
def main(args:Array[String]) 
{ 
val myStream: Stream[Int] = cons(2, cons(4, cons(6, cons(9, Stream.empty))))
print("Accessing Stream : ")
print(myStream) 
print("\nTake first 2 elements of stream : ") 
myStream.take(2).print
print("\nTake all elements from stream : ") 
myStream.take(5).print
} 
}

Output

输出量

Accessing Stream : Stream(2, <not computed>)
Take first 2 elements of stream : 2, 4
Take all elements from stream : 2, 4, 6, 9

Creating an empty Stream

创建一个空流

You can create an empty stream in Scala using Stream.empty.

您可以使用Stream.empty在Scala中创建一个空流。

object myObject 
{ 
def main(args:Array[String]) 
{ 
val myStream: Stream[Int] = Stream.empty[Int] 
print("This is an empty Stream : ") 
println(myStream)
} 
}

Output

输出量