It’s just the syntax differences between the two languages for how to write a lambda.

Java lambdas were unfortunately added long after the original language was already designed, so for backward compatibility it’s a bit harder to read.

But maybe you’re just asking if you can put the lambda inside the function parentheses? You can still do that in Kotlin, but the compiler will give you a warning because it’s less readable.

val postalCode: LiveData<String> = Transformations.switchMap(addressInput, {
                address -> repository.getPostCode(address) })

Also, your first piece of code is not a function declaration…it’s a property assignment. Your Kotlin property assigns it one time at class initialization, whereas your Java method creates a new instance each time it’s called.

This is a Kotlin function declaration

 val postalCode: LiveData<String> = Transformations.switchMap(addressInput) {
                    address -> repository.getPostCode(address) }

This is a Java function declaration

public final LiveData<String> postalCode(){
        Transformations.switchMap(addressInput, (address) -> {
            return repository.getPostCode(address);
         })};

1 – Why is not possible to declare in Kotlin something like this :

... .(addressInput, (address) -> {
            return repository.getPostCode(address);
         })

,pleae show how is posible to make a delaration like Java.