If you are writing new code in Kotlin, or converting a SAM interface which is used only at a few places, leverage the Kotlin function as a first-class citizen for both definition and consumption. One thing worth doing is to make sure the SAM is annotated with that IntelliJ can validate if the annotated target always satisfies the definition of a SAM. Less worry for you if you are not planning to convert SAM interface to Kotlin yet (say in an external dependency). The method body refers to the interface itself by this.The interface or abstract class is written in Kotlin.

SAM conversion is not fully supported in the following scenarios: In other words, Kotlin supports SAM conversion only if the interface with a single abstract method is defined in Java. Because the function is regarded as a first-class citizen, Kotlin does not need to support converting functions into implementations of Kotlin interfaces for SAM. This indicates that functions can be stored in variables and data structures, passed as arguments to and returned from other higher-order functions. When a lambda expression does nothing but calling an existing method, method reference can be used to make the code even more concise. Lambda expression simplifies Java code by more compactly allowing users to express instances of single-method classes. It can be combined with lambda expression and method reference in Java. Functional interface, also known as SAM ( Single Abstract Method), was introduced to Java 8.

Convert java code to kotlin