This question already has an answer here:
functional interface that takes nothing and returns nothing [duplicate]
(1 answer)
Closed 4 years ago.
I was looking for a functional interface provided by java.util package which do not take argument and returns void. There are number of Functional interfaces in java.util package like Consume and Supplier, but i am looking for a functional interface without argument and without return type. I know that i can create some interface like 'Operation' which will serve my purpose, but if it is already available in java.util, it would be good to use.
You're looking for java.lang.Runnable
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This question already has answers here:
"private[syntax]" in Scala [duplicate]
(1 answer)
Private scoping with square brackets (private[...]) in Scala
(2 answers)
Closed 2 years ago.
I am new to scala and don't know what does private[wikipedia]mean,could anyone please tell me?Is it a generic type?
package wikipedia
import scala.io.Source
object WikipediaData {
private[wikipedia] def lines: List[String] = ???
It's a way to scope the privacy of a given object. So private[wiki] means only code defined within wiki has access to lines.
See here: https://alvinalexander.com/scala/how-to-control-scala-method-scope-object-private-package/
private[packageX] means the following method/class/object/constructor is accessible only from within that package - in this case syntax is the package name, and this constructor is only accessible from other code inside syntax package.
This question already has answers here:
Understanding implicit in Scala
(7 answers)
Closed 3 years ago.
Every spark program has this line import spark.implicits._. When I looked online to understand the use of "implicits" in scala, I got this definition:
Scala "implicits" allow you to omit calling methods or referencing variables directly but instead rely on the compiler to make the connections for you
I understand the definition but it brings me the below doubts.
Isn't it the same with any other import statement ? Every import statement would bring the functions/options/methods we would like to use them in the code.
If implicits are different to regular import statement, what do they bring to the table and how are they different ?
Could anyone explain the real use case of implicits parameters & functions
in scala ?
Isn't it the same with any other import statement ?
It is. implicits in spark.implicits is just a name, and
import spark.implicits._
is only unusual because it imports members of an instance, which many other languages with something like import can't do (but Scala can).
If you look at docs for implicits you'll see its members are marked as implicit which is what actually makes them implicit.
This question already has answers here:
What's the difference between multiple parameters lists and multiple parameters per list in Scala?
(4 answers)
Closed 4 years ago.
What is the difference and advantage of using those two ways of writing a function (and how the first way of writing a function is called):
def do_something(a:String, b:String)(c:String) :Unit = {}
and
def do_something(a:String, b:String, c:String) :Unit = {}
It is called Currying, Hier you find a description:
scala-currying
The advantage is that you can partially apply such a function.
Here from the linked article:
One benefit is that Scala currying makes creating anonymous functions easier.
Scala Currying also makes it easier to pass around a function as a first-class
This question already has answers here:
How do I obtain ctor argument types via reflection in Scala 2.10.1
(3 answers)
Closed 8 years ago.
I have a Scala class as follows:
class Test(val one: String, val two: Int) {}
How can I find the names of the constructor parameters and the types of the parameters in code?
You can see how to use reflection in Scala (2.10 and above) in the docs. This explains how to instantiate reflected classes or get the types of the parameters.
About the parameter names, I don't think they are kept after the compilation.
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Scala equivalent of Java java.lang.Class<T> Object
Hi all,
I can not call a java classname.class method in scala, but scala guarantee that I can call any java method in scala, so why I can not call ClassName.class method
Jeff Zhang
T.class is actually not a method or a field but a special form that instructs the Java compiler that you are referring to the run-time representation of the class. The equivalent special form in Scala is classOf[T].
Your subject asks a different question, which is if you can call .getClass() for any object. The answer to that is yes, but that does something different --- for a given instance of a class T, it gives you T. So although in the end you still get the run-time representation T, the starting point is different --- an instance of T rather than a name/symbol representing T itself.
To put these ideas together, note that T.class.getClass() (or classOf[T].getClass in Scala) will always give you the runtime representation of java.lang.Class for any T. Amusingly, this is both the runtime representation of java.lang.Class, and also an instance of java.lang.Class itself since Java, unlike some languages, does not have metaclasses.
For a class A, just use classOf[A] instead to get the class object.