Kotlin - not able to find kotin equivalent of java.util.function.Function<T, R>

I am trying to convert one of the java function which takes java.util.function.Function<T, R> to Kotlin using IDEA 2019.3 Kotlin multiplatform library.

But t I could not find a way to do an equivalent function in kotlin. I can see here that there is Function1 to do a java interoperability but I am not able to do any import from import kotlin.jvm.functions.*

I am trying Kotlin for the first time. Could someone please tell what am I doing wrong.

Update- Please see my java code

import java.util.function.Function;

public class A {
	Function<String, String> function;

	public A(Function<String, String> function) {
		super();
		this.function = function;
	}
	
public String convert(String input) {
	return function.apply(input);
	
}
}

Not clear about your question, but assuming you are trying to duplicate functionality from Java:

In Kotlin, you do not use Function interfaces directly because functions are first-class. The Function1, Function2, etc. classes are only used to make functions available to Java code and the JVM.

If you want to create the equivalent of a Java Function<T, R>, you would define a function using either Kotlin's fun or lambda syntax.

fun getStringLength(x: String): Int {
    return x.length
}

//...
val functionReference = ::getStringLength
// Java code will treat this as a Function1<String, Int>

or

val function = fun (x: String): Int {
    return x.length
}
// Java code will treat this as a Function1<String, Int>

or

val functionReference = { x: String -> x.length }
// Java code will treat this as a Function1<String, Int>

To declare that a function takes a function as a parameter, you use (input) -> output syntax as the variable type:

fun <T, R> doSomething(functionalReference: (T) -> R) {
    //
}

You can call a function using its referenced name:

fun <T, R> doSomething(input: T, functionalReference: (T) -> R): R {
    return functionalReference(input)
}

Sounds like you want to convert a Java function that accepts a Function to an equivalent Kotlin function.

Example:

Java

public class JavaFunctions {
   public static <T,R> void runAFunction(Function<T, R> userFunction){
      userFunction.apply(null);
   }
}

Kotlin (These two functions are equivalent)

class KotlinFunctions{
   companion object{
      @JvmStatic
      fun <T,R> runAFunction(userFunction:(T?) -> R?){
         userFunction.invoke(null);
      }

      @JvmStatic
      fun <T,R> runAFunction2(userFunction: Function1<T?, R?> ){
         userFunction.invoke(null);
      }
   }
}