function.kt

// FILE: 1.kt
package p3

class A {
    fun<T> inTransaction(block: (tran: String) -> T): T {
        println("Function 1")
        return block("")
    }

    fun inTransaction(block: (tran: String) -> Unit) {
        println("Function 2")
    }
}

// FILE: B.java
package p3;

import kotlin.Unit;
import kotlin.jvm.functions.Function1;

public class B {
    public static void main(String[] args) {
        A a = new A();
        Function1<String, Integer> fInt = x -> 4;
        a.inTransaction(fInt);

        Function1<String, Unit> fString = x -> Unit.INSTANCE;
        a.inTransaction(fString);
    }
}