Implicit type conversion of Java – lambda expressions

Consider the following courses:

public void method() {
    test(() -> { });
}

void test(Runnable a) {
    System.out.println("Test 1");
}

void test(A a) {
    System.out.println("Test 2");
}

interface A extends Runnable {

}

Calling method () will result in test 2 output This means that the lambda expression () – > {} is implicitly converted to A. why?

Solution

This is the same standard rule for all overloads Java will choose the most specific applicable method.

Both methods accept parameters of a function interface type lambda expressions

() -> { }

Can be converted to these two types A is a subclass of runnable, so it is more specific Therefore, select the method with parameter type A