Kotlin is a language that is designed to maintain interoperability with Java code. The following example shows a nuance that we should take into account when we invoke Kotlin code from Java code. Let's create a simple Kotlin function that throws an exception:

fun testMethod() {
    throw IOException()
}

This function can be called from Java code like this:

public class Example5 {
    public static void main(String[] args) {
        Example5Kt.testMethod();
    }
}

And this code can be compiled. This behavior can be unexpected for a Java developer who is used to dealing with checked exceptions. See what happens if we write something like this:

public static void testMethod() {
    throw new IOException();
}

The compiler will show the following error:

Error:(11, 9) java: unreported exception java.io.IOException; must be caught or declared to be thrown

To fix this error, we have to add the @Throws annotation, as follows:

@Throws(IOException::class)
fun testMethod() {
    throw IOException()
}

public static void main(String[] args) {
    try {
        Example5Kt.testMethod();
    } catch (IOException e) {
        e.printStackTrace();
    }
}