I'm trying to read a list of string from a file, which is structured as a list:
ElemA
ElemB
ElemC
I need to save into this variable, which is defined as:
private var history: Array<out String>?
I made this method, but it doesn't works because it requires an Array? as output, but it founds an Array<(out) Any!>!
private fun loadHistory(): Array<out String>? {
val list = ArrayList<String>()
File("history").forEachLine { list.add(it) }
return list.toArray()
}
How can I solve?
As suggested by #jsamol in the comments.
You should use toTypedArray() instead of toArray() to get an array of the specific type.(ref)
toArray() returns new array of type Array<Any?>. (ref)
private fun loadHistory(): Array<out String>? {
val list = ArrayList<String>()
File("history").forEachLine { list.add(it) }
return list.toTypedArray()
}
Related
Hello actually I'm developing an app with the use of USB, I need return the UsbConfiguration from this map structure but the compiler error is:
Type checking has run into a recursive problem. Easiest workaround: specify types of your declarations explicitly
This is the call from the method:
#RequiresApi(Build.VERSION_CODES.LOLLIPOP)
private fun getConfiguration(index:Int?):
Map<String, Any> {
val device = usbDevice
val configuration: UsbConfiguration = device!!.getConfiguration(index!!)
val map = configuration.toMap() + ("index" to index)
return map
}
And this is the part with the problem specific in getInterface(it).toMap():
fun UsbConfiguration.toMap() = mapOf(
"id" to id,
"interfaces" to List(interfaceCount) {
getInterface(it).toMap() }
)
The code from library to the method getInterface(int index)
#NonNull
public UsbInterface getInterface(int index) {
throw new RuntimeException("Stub!");
}
I have two different pieces of code. In one i need to use object and in the second i'm not.
Can someone explain me the difference between the situation:
first Code:
private val onInitWebResponseHandler: VolleyHandler.WebResponseHandler = VolleyHandler.WebResponseHandler()
{
Thread(ParseJsonStringOnInit(WeakReference(this),
weakRefIOnAllScoresDataFirstFetched, it)).start()
}
Second Code:
val competitionOrderLevelComparator : Comparator<CompetitionObj> = object : Comparator<CompetitionObj> {
override fun compare(object1: CompetitionObj, object2: CompetitionObj): Int
{
return object1.orderLevel - object2.orderLevel
}
}
fun interface WebResponseHandler
{
fun onWebResponseFinished(jsonString:String?)
}
In addition how the first code, we can have () brackets if interface doesn't have a constructor?
Looking for solution how to match objects from list with data from map with condition if object field starts with map values and save to another map with Groovy
i have map with some data
Map<String, String> dataMap = new HashMap()
dataMap.put("d1", "DATA1")
dataMap.put("d2", "DATA2")
dataMap.put("d3", "DATA3")
and list of DataElement objects
List<DataElement> elements = new ArrayList()
elements.add(new DataElement("TEXT1"))
elements.add(new DataElement("TEXT2"))
elements.add(new DataElement("DATA1_text1"))
elements.add(new DataElement("DATA2_text2"))
class DataElement {
public field;
public DataElement(String text){
this.field = text
}
public getField(){
return this.field
}
And i'am trying to get new Map where keys are values from first map and values are objects(field) from List with condition if object field starts with map value: Result should be:
[d1=DATA1_text1, d2=DATA2_text2]
My code is working but may be there is more elegant variant with using collectEntries:
list = new HashMap()
mapping = dataMap.each { key, v ->
elements.each { el ->
if (el.getField().startsWith(v)) {
list.put(key, el)
}
}
}
dataMap.collectEntries{k,v->
[k,elements.find{e-> e.getField().startsWith(v)} ]
}.findAll{k,v-> v} //to keep only non empty values
I am trying to figure out if I can work with Kotlin and Spark,
and use the former's data classes instead of Scala's case classes.
I have the following data class:
data class Transaction(var context: String = "", var epoch: Long = -1L, var items: HashSet<String> = HashSet()) :
Serializable {
companion object {
#JvmStatic
private val serialVersionUID = 1L
}
}
And the relevant part of the main routine looks like this:
val transactionEncoder = Encoders.bean(Transaction::class.java)
val transactions = inputDataset
.groupByKey(KeyExtractor(), KeyExtractor.getKeyEncoder())
.mapGroups(TransactionCreator(), transactionEncoder)
.collectAsList()
transactions.forEach { println("collected Transaction=$it") }
With TransactionCreator defined as:
class TransactionCreator : MapGroupsFunction<Tuple2<String, Timestamp>, Row, Transaction> {
companion object {
#JvmStatic
private val serialVersionUID = 1L
}
override fun call(key: Tuple2<String, Timestamp>, values: MutableIterator<Row>): Transaction {
val seq = generateSequence { if (values.hasNext()) values.next().getString(2) else null }
val items = seq.toCollection(HashSet())
return Transaction(key._1, key._2.time, items).also { println("inside call Transaction=$it") }
}
}
However, I think I'm running into some sort of serialization problem,
because the set ends up empty after collection.
I see the following output:
inside call Transaction=Transaction(context=context1, epoch=1000, items=[c])
inside call Transaction=Transaction(context=context1, epoch=0, items=[a, b])
collected Transaction=Transaction(context=context1, epoch=0, items=[])
collected Transaction=Transaction(context=context1, epoch=1000, items=[])
I've tried a custom KryoRegistrator to see if it was a problem with Kotlin's HashSet:
class MyRegistrator : KryoRegistrator {
override fun registerClasses(kryo: Kryo) {
kryo.register(HashSet::class.java, JavaSerializer()) // kotlin's HashSet
}
}
But it doesn't seem to help.
Any other ideas?
Full code here.
It does seem to be a serialization issue.
The documentation of Encoders.bean states (Spark v2.4.0):
collection types: only array and java.util.List currently, map support is in progress
Porting the Transaction data class to Java and changing items to a java.util.List seems to help.
Given:
public struct Id
{
readonly int m_id;
public Id(int id)
{ m_id = id; }
public static implicit operator int(Id id)
{ return id.m_id; }
public static implicit operator Id(int id)
{ return new Id(id); }
}
Can you implicitly convert an
IEnumerable<int>
to
IEnumerable<Id>
and vice versa. In some way. Note that
var ids = new int[]{ 1, 2 };
ids.Cast<Id>();
does not appear to work and covariance does not appear to be working in this case, either. Of course, doing a select will work i.e.:
ids.Select(id => new Id(id));
But I am looking for something that would make this work implicitly, so writing:
IEnumerable<Id> ids = new int[]{ 1, 2 };
And yes, I know this can be written as:
IEnumerable<Id> ids = new Id[]{ 1, 2 };
But the issue is in cases where the enumerable of ints comes from a different source, such as a file for example.
I am sorry if there already is an answer for this, but I could not find it.
According to this answer what you want is not possible. But you can get close by not implicitly casting your id but your collection. Like this :
public class Ids : List<int>
{
public static implicit operator Ids(int[] intArray)
{
var result = new Ids();
result.AddRange(intArray);
return result;
}
}
then this is possible :
Ids t = new [] { 3,4 };
What's wrong with:
IEnumerable<int> data = GetDataFromSource();
IEnumerable<Id> ids = data.select(id => new Id(id));