什么是Kotlin函数类型的java等效项？

Question

I have code in Kotlin and test code in Java . Since Kotlin and Mockito aren't best friends, I haven't migrated test code to Kotlin .

In Kotlin I have methods with block types. For example:

open fun getProductInfo(resultListener: (List<Deal>)->Unit, errorListener: (Throwable)->Unit)
{
    ...
}

Now I want to stub this method in Java tests. What's the java equivalent of the types? In other words, what should I write in place of ???s below:

doAnswer(invocation -> {
    ??? resultListener = (???) invocation.getArguments()[0];
    // call back resultListener
    return null;
}).when(api).getProductInfo(any(), any());

Answer 1

From the Kotlin in Action book:

The Kotlin standard library defines a series of interfaces, corresponding to different numbers of function arguments: Function0<R> (this function takes no arguments), Function1<P1, R> (this function takes one argument), and so on. Each interface defines a single invoke method, and calling it will execute the function.

In this case, these two functions are both Function1 instances, since they are functions that take one parameter:

Mockito.doAnswer(invocation -> {
    Function1<List<Deal>, Unit> resultListener =
            (Function1<List<Deal>, Unit>) invocation.getArguments()[0];
    Function1<Throwable, Unit> errorListener =
            (Function1<Throwable, Unit>) invocation.getArguments()[1];

    resultListener.invoke(new ArrayList<>());

    return null;
}).when(api).getProductInfo(any(), any());

---

On another note, you could try mockito-kotlin and the inline version of Mockito to write your tests in Kotlin as well.

Answer 2

Why not to try in Android Studio or IntelliJ, to get Java code from Kotlin:

• Menu -> Tools -> Kotlin -> Show Kotlin Bytecode
• Click on the -> Decompile Button
• Copy the Java code

This way you can continue your work with Mockito, unfortunately you will get redundant lines of code (not much) because Kotlin deal with bytecode.