[英]Scala list print issue — IntelliJ IDEA
I have the following code 我有以下代码
object DispatchLibrary
{
private var nodes = Map.empty[java.util.UUID, List[BigInt]]
def addNode(uuid: java.util.UUID) = if(nodes contains uuid) nodes else (nodes += (uuid -> Nil))
def addValue(uuid: java.util.UUID, value: BigInt) = nodes + (uuid -> (value :: (nodes get uuid getOrElse Nil)))
//def getValue(uuid: java.util.UUID) : List[BigInt] = ???
//def getValues() : List[BigInt] = ???
def calculated(): Boolean = !nodes.exists(_._1 eq null)
def main(args: Array[String]) : Unit =
{
val uuid = java.util.UUID.randomUUID()
addNode(uuid)
addValue(uuid, BigInt(999))
addValue(uuid, BigInt(9999))
nodes foreach {case (key, value) => println (key + "->" + value)}
}
}
Running the above code in IntelliJ IDEA gives something similar to the following output 在IntelliJ IDEA中运行上面的代码给出了类似于以下输出的内容
8b2b4a7b-3e65-4de0-9035-8ee1d2910983->List()
I am not sure why the List is not being printed. 我不确定为什么列表没有打印。
Running a similar code from the REPL gives the expected output 从REPL运行类似的代码可以得到预期的输出
scala> var nodes = Map.empty[Int, List[BigInt]]
nodes: scala.collection.immutable.Map[Int,List[BigInt]] = Map()
scala> nodes += (1->Nil)
scala> nodes += (1 -> (BigInt(999) :: (nodes get 1 getOrElse Nil)))
scala> nodes += (1 -> (BigInt(9999) :: (nodes get 1 getOrElse Nil)))
scala> nodes foreach {case (key, value) => println (key + "-->" + value )}
1-->List(9999, 999)
I would appreciate also if you could help me in writing the commented methods. 如果你能帮我写评论方法,我将不胜感激。
In your addValue
method you write nodes + (uuid -> (value :: (nodes get uuid getOrElse Nil)))
which does not change the list in nodes
, but only creates a new copy with the value added. 在你的
addValue
方法中你编写nodes + (uuid -> (value :: (nodes get uuid getOrElse Nil)))
这不会改变nodes
的列表,但只创建一个添加了值的新副本。 Since Map
is immutable by default you'll have to store it like you do with the =
-sign in the addNode
method. 由于默认情况下
Map
是不可变的,因此您必须像在addNode
方法中使用=
-sign一样存储它。
The reason it prints anything at all is because the first entry consists of a UUID (String) and Nil (empty List). 它打印任何东西的原因是因为第一个条目包含UUID(String)和Nil(空List)。 The "8b2b4a7b-3e65-4de0-9035-8ee1d2910983" makes sense then because it's the UUID.
“8b2b4a7b-3e65-4de0-9035-8ee1d2910983”之所以有意义,是因为它是UUID。 The "List()" is a result of printing Nil (since it is an empty List).
“List()”是打印Nil的结果(因为它是一个空列表)。
And there you have it. 你有它。 Try writing
node += ...
in the addValue
in stead. 尝试在
addValue
中编写node += ...
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