Why the code in an object expression can access variables from the scope that contains it in kotlin?

Question

In Kotlin,the code in an object expression can access variables from the scope that contains it, just like the following code:

fun countClicks(window: JCompo         


        

Answer 1

The concept you're referring to is called "capturing".

There's a trick that can be applied in Java: Wrap the mutable value into a final wrapper such as AtomicReference and the compiler will stop complaining:

AtomicReference max = new AtomicReference<>(10);
if (System.currentTimeMillis() % 2 == 0) {
    max.set(11)
}
Predicate pred = i -> i * 2 > max.get();

That's basically what's happening in Kotlin as well: If a final variable (val) is being captured, it simply gets copied into the lambda. But if, on the other hand, a mutable variable (var) is being captured, its value is wrapped in an instance of Ref:

class Ref(var value: T)

The Ref variable is final and therefore can be captured without a problem. As a result, the mutable variable can be changed from within the lambda.