How to know if two classes implement a common interface?

Question

Is there an easy way to check if two classes implement a common interface? I am using IntelliJ, and calling a Java library (Elastic Java High Level REST Client) from some Kotlin code.

SearchHit and GetResponse classes both have getId() and getSourceAsString() methods. How can I know if they implement a common interface, so that I can mutualize my functions that take these objects as parameters ?

This is my code :

    fun JsonAdapter<Descriptor>.fromHit(hit: SearchHit): Descriptor {
        val descriptor = this.fromJson(hit.sourceAsString)
        if (descriptor == null) {
            throw BadFormatException("Json descriptorDeserializer returned a null value")
        }

        descriptor.descriptorId = hit.id
        return descriptor
    }

    fun JsonAdapter<Descriptor>.fromResponse(response: GetResponse): Descriptor {
        val descriptor = this.fromJson(response.sourceAsString)
        if (descriptor == null) {
            throw BadFormatException("Json descriptorDeserializer returned a null value")
        }

        descriptor.descriptorId = response.id
        return descriptor
    }

Answer 1

Run Time

You can try the is keyword in Kotlin to check if an object is an instance of some interfaces :

if (obj is MyInterface) {...}

Which is the Kotlin equivalent of the Java :

if (obj instanceof MyInterface) {
    //...
}

During Development

During development with Intellij Idea , we can quickly check classes declaration by pressing Ctrl + B when the cursor is on the class name.

Answer 2

If you don't know which interface is implemented by your classes you can use the following code to get a list of these interfaces. You'll get a list of classes that you can compare do see if your objects share a common interface.

val obj = MyClass()   
var interfaces = obj.javaClass.interfaces