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SAM stands for Single Abstract Method interface and it’s called also Functional interface. Functional interface is an interface with only one non-default method and any number of default methods. In Kotlin you can use Java or Kotlin Functional interfaces as a Lambda expression for example. The same syntax will work on Kotlin also if your functional interface is written in Java like OnClickListener. The syntax is not an extension but SAM conversion, but what does SAM stand for? You can use the same syntax to call your custom listener like setOnClick listener.