CODEWITHSUNDEEP
kotlinjava-stream
hades
hades

Reputation: 4696

Kotlin add custom method to stream chaining

I need to add a custom method (which is a Consumer) to the dot chaining in stream api, i not sure how to do it, following is my code.

If that is not possible, is there anyway to do it with other operation? Maybe like with .map or something else?

fun main(args: Array<String>) {
    var countries: List<String> = listOf("India", "Germany", "Japan")

    var firstCountry = countries.stream()
                                .filter{it == "Germany"}
                                .performOperation{}    //not sure what to do here
                                .findFirst()

    println(firstCountry)

}


fun performOperation(country: String) {
    if(country.length > 3) {
        throw InvalidLengthException("Error")
    }
    
   //do some operation, won't return any value
   doCustomOperation(country)
}

Upvotes: 1

Views: 428

Answers (2)

DownloadPizza
DownloadPizza

Reputation: 3466

There is two ways to do what you want.

    var firstCountry = countries.stream()
                                .filter{it == "Germany"}
                                .also(::performOperation)
                                .findFirst()

The :: is a function reference and is basically the same as .also { performOperation(it)}

The second one would be to make your own extension method on list. I wouldn't recommend it until you understand kotlin lambdas and extension methods

fun Stream<String>.performOperation(): Stream<String> {
  for(country in this) {
    if(country.length > 3) {
        throw InvalidLengthException("Error")
      }
    
   doCustomOperation(country)
   } 
  return this
}

You would just call that one like .performOperation() where you have the .performOperation{}

Upvotes: 1

mightyWOZ
mightyWOZ

Reputation: 8315

You may already be aware that when it comes to steams there are two types of operations, one is your map, filter etc. known as intermediate opeartion and others are terminal operations such as forEach. You said your custom operation wont return any value, hence making it a terminal operation. moreover it seems to me that you want to perform same operation for all the elements, basically a forEach. for this you can define an extension function on Stream as

fun <T> Stream<T>.someOperation(operation: (T) -> Unit){
    this.forEach { operation(it) }
}

Upvotes: 1

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