inline fun <T, R : Any> Array<out T>.mapNotNull(
transform: (T) -> R?
): List<R>
My use case is a little different than this one
Is there any function that I can use in the place of mapNotNull in Java?
val strings: List<String> = listOf("12a", "45", "", "3")
val ints: List<Int> = strings.mapNotNull { it.toIntOrNull() }
println(ints) // [45, 3]
There are no direct solution, but the equivalent of the code in java, can be:
List<Integer> ints = strings.stream()
.filter(s -> s.matches("[0-9]+"))
.map(Integer::valueOf)
.collect(Collectors.toList());
Outputs
[45, 3]
From the documentation:
fun String.toIntOrNull(): Int?Parses the string as an Int number and returns the
resultornullif the string is not a valid representation of a number.
So if we want to create the exact code in java, then you can use:
.map(s -> s.matches("[0-9]+") ? Integer.valueOf(s) : null)
And then:
Returns a list containing only the non-null results of applying the given
Which lead you to use in java:
.filter(Objects::nonNull)
your final code should be:
List<Integer> ints = strings.stream()
.map(s -> s.matches("[0-9]+") ? Integer.valueOf(s) : null)
.filter(Objects::nonNull)
.collect(Collectors.toList());
But the first solution still the better one for your case.
Scanner is a nice way to check for the presence of integers:
List<String> strings = List.of("12a", "45", "", "3");
List<Integer> ints = strings.stream()
.filter(it -> new Scanner(it).hasNextInt())
.map(Integer::parseInt)
.collect(Collectors.toList());
System.out.println(ints); // [45, 3]