There's more...

It's important to keep in mind that, although we can define a default function implementation in the interface, we are not able to instantiate default values for interface properties. Unlike the class properties, properties of an interface are abstract. They don't have backing fields that could hold a current value (state). If we declare a property inside an interface, we need to implement it in the class or object that implements this interface. This is the main difference between interfaces and abstract classes. Abstract classes can have constructors and can store properties along with their implementations.

As with Java, we can't extend multiple classes; however, we can implement multiple interfaces. When we have a class implementing multiple interfaces containing default implementations, we are at risk of dealing with conflicts caused by functions having the same signatures:

interface A {
    fun foo() {
        // some operations 
    }
}

interface B {
    fun foo() {
        // other operations
    }
}

In this case, we need to override the foo() function explicitly to resolve the conflict:

class MyClass: A, B {
    override fun foo() {
        print("I'm the first one here!")
    }
}

Otherwise, we would get the following error:

Class 'MyClass' must override public open fun foo(): Unit because it inherits multiple interface methods of it.