I saw this in java code.
"anObject?.property" and
"anObject?.getProperty()".
I have tried look for it online. But could not find any.
What does "?." mean here in Java?
This does not exists is Java
You may find this in Kotlin and this is called null safety
val a = "Kotlin"
val b: String? = null
println(b?.length)
println(a?.length)
Related
I have tried to get all the solution files(*.sln) in a given path and print it individually by split the string(each solution file path) using comma delimiter. Programming script language am using is Jenkins Groovy. Am getting the below specified error when build the Jenkins job. Any one please look into this and guide me to proceed in a right way.
def finder = new FileNameFinder()
def files = finder.getFileNames 'D:\jobs', '**/*.sln'
def resultList = files.tokenize(",")
for(i=0; i<resultList.size();i++)
{
println resultList[i]
}
Error Details:
hudson.remoting.ProxyException: groovy.lang.MissingMethodException: No signature of method: java.util.ArrayList.tokenize() is applicable for argument types: (java.lang.String) values: [,]
Possible solutions: toUnique(), toUnique(), toUnique(java.util.Comparator), takeWhile(groovy.lang.Closure), toUnique(groovy.lang.Closure), toUnique(java.util.Comparator)
Thanks in advance!!
Myself itself found an answer for my above problem. Please find below the modified working code.
def finder = new FileNameFinder()
def files = finder.getFileNames 'D:\jobs', '**/*.sln'
assert files instanceof List
println files.size()+" solution files found in the given path. Below are the found solution files details. \n"
for(i=0;i<files.size();i++)
{
println files[i];
}
Thanks
This seems like a simple question, but it's very challenging to search for, so I'm asking a new question. My apologies if it's already been asked.
Due to the compiler bug described here Scala 2.11.5 compiler crash with type aliases and manifests (also here https://issues.scala-lang.org/browse/SI-9155), I need to use scala TypeTags and friends for discovery of type parameters to methods. However, I then need to use that type information in a Java library that uses java.lang.Class and java.lang.reflect.Type.
How can I convert a scala.reflect.runtime.universe Type into a java.lang.reflect.Type or java.lang.Class?
Put concretely, how would I fill out the body of this method:
def typeFor[T](implicit tag: TypeTag[T]): java.lang.reflect.Type = ...
or, if that's not possible:
def typeFor[T](implicit tag: TypeTag[T]): java.lang.Class[T] = ...
And note, due to the bug posted above, I cannot use scala.reflect.Manifest.
The short answer is no, but you can try to do something similar to this SO question. However there is an open ticket....
This may have some limitations I'm not aware of, but you could drop down to Java reflection and try something like:
import scala.util.control.Exception._
def typeMe[T](implicit t: TypeTag[T]) = {
catching(classOf[Exception]) opt Class.forName(t.tpe.typeSymbol.asClass.fullName)
}
println(typeMe[String])
println(typeMe[ClassTag[_]])
Results in:
Some(class java.lang.String)
Some(interface scala.reflect.ClassTag)
The way I solved it with manifests, was:
private def typeFromManifest(m: Manifest[_]): Type = {
if (m.typeArguments.isEmpty) { m.runtimeClass }
else new ParameterizedType {
def getRawType = m.runtimeClass
def getActualTypeArguments = m.typeArguments.map(typeFromManifest).toArray
def getOwnerType = null
}
}
Right now I'm trying to solve this using something other than Manifest which should be removed from scala runtime.
I've been stuck on this particular problem for about a week now, and I figure I'm going to write this up as a question on here to clear out my thoughts and get some guidance.
So I have this case class that has a java.sql.Timestamp field:
case class Request(id: Option[Int], requestDate: Timestamp)
and I want to convert this to a JsObject
val q = Query(Requests).list // This is Slick, a database access lib for Scala
printList(q)
Ok(Json.toJson(q)) // and this is where I run into trouble
"No Json deserializer found for type List[models.Request]. Try to implement an implicit Writes or Format for this type." Okay, that makes sense.
So following the Play documentation here, I attempt to write a Format...
implicit val requestFormat = Json.format[Request] // need Timestamp deserializer
implicit val timestampFormat = (
(__ \ "time").format[Long] // error 1
)(Timestamp.apply, unlift(Timestamp.unapply)) // error 2
Error 1
Description Resource Path Location Type overloaded method value format with alternatives:
(w: play.api.libs.json.Writes[Long])(implicit r: play.api.libs.json.Reads[Long])play.api.libs.json.OFormat[Long]
<and>
(r: play.api.libs.json.Reads[Long])(implicit w: play.api.libs.json.Writes[Long])play.api.libs.json.OFormat[Long]
<and>
(implicit f: play.api.libs.json.Format[Long])play.api.libs.json.OFormat[Long]
cannot be applied to (<error>, <error>)
Apparently importing like so (see the documentation "ctrl+F import") is getting me into trouble:
import play.api.libs.json._ // so I change this to import only Format and fine
import play.api.libs.functional.syntax._
import play.api.libs.json.Json
import play.api.libs.json.Json._
Now that the overloading error went away, I reach more trubbles: not found: value __ I imported .../functional.syntax._ already just like it says in the documentation! This guy ran into the same issue but the import fixed it for him! So why?! I thought this might just be Eclipse's problem and tried to play run anyway ... nothing changed. Fine. The compiler is always right.
Imported play.api.lib.json.JsPath, changed __ to JsPath, and wallah:
Error 2
value apply is not a member of object java.sql.Timestamp
value unapply is not a member of object java.sql.Timestamp
I also try changing tacks and writing a Write for this instead of Format, without the fancy new combinator (__) feature by following the original blog post the official docs are based on/copy-pasted from:
// I change the imports above to use Writes instead of Format
implicit val timestampFormat = new Writes[Timestamp]( // ERROR 3
def writes(t: Timestamp): JsValue = { // ERROR 4 def is underlined
Json.obj(
/* Returns the number of milliseconds since
January 1, 1970, 00:00:00 GMT represented by this Timestamp object. */
"time" -> t.getTime()
)
}
)
ERROR 3: trait Writes is abstract, cannot be instantiated
ERROR 4: illegal start of simple expression
At this point I'm about at my wits' end here, so I'm just going back to the rest of my mental stack and report from my first piece of code
My utter gratefulness to anybody who can put me out of my coding misery
It's not necessarily apply or unapply functions you need. It's a) a function that constructs whatever the type you need given some parameters, and b) a function that turns an instance of that type into a tuple of values (usually matching the input parameters.)
The apply and unapply functions you get for free with a Scala case class just happen to do this, so it's convenient to use them. But you can always write your own.
Normally you could do this with anonymous functions like so:
import java.sql.Timestamp
import play.api.libs.functional.syntax._
import play.api.libs.json._
implicit val timestampFormat: Format[Timestamp] = (
(__ \ "time").format[Long]
)((long: Long) => new Timestamp(long), (ts: Timestamp) => (ts.getTime))
However! In this case you fall foul of a limitation with the API that prevents you from writing formats like this, with only one value. This limitation is explained here, as per this answer.
For you, a way that works would be this more complex-looking hack:
import java.sql.Timestamp
import play.api.libs.functional.syntax._
import play.api.libs.json._
implicit val rds: Reads[Timestamp] = (__ \ "time").read[Long].map{ long => new Timestamp(long) }
implicit val wrs: Writes[Timestamp] = (__ \ "time").write[Long].contramap{ (a: Timestamp) => a.getTime }
implicit val fmt: Format[Timestamp] = Format(rds, wrs)
// Test it...
val testTime = Json.obj("time" -> 123456789)
assert(testTime.as[Timestamp] == new Timestamp(123456789))
The following code throws an error "Class not found: org.apache.ws.security.WSConstants"
<cfset variables.WSConstantsObj = CreateObject("Java","org.apache.ws.security.WSConstants")>
I'm not sure if this should just work out of the box or whether there is something else I need to do to instantiate this java object.
Can anyone help?
I appear to have figured it out.
Needed a couple of other jar files loaded first, in my particular instance.
variables.paths = arrayNew(1);
variables.paths[1] = getDirectoryFromPath(getCurrentTemplatePath()) & "lib\wss4j-1.5.8.jar";
variables.paths[2] = getDirectoryFromPath(getCurrentTemplatePath()) & "lib\xmlsec-1.4.2.jar";
variables.loader = createObject("component","lib.javaloader.JavaLoader").init(loadPaths=variables.paths,loadColdFusionClassPath=true);
variables.WSConstantsObj = loader.create("org.apache.ws.security.WSConstants");
In cpp file I have std::round(double)
Please can I know the equivalent code in Java
Edit: I am already using java.lang.Math.round(double) and getting match in 99% cases. But in some places iam getting mismatch. For example:
std::round(4816.5058) = 4816 and Math.round(4816.5058) = 4817
std::round(4466.49996) = 4467 and Math.round(4466.49997) = 4466
java.lang.Math.round(double)