Casting in lambdas, marked as redundant in IntelliJ

Question

I'm writing a small framework that needs to use instanceof to know which type of callback is being passed. I already know the disadvantages of instanceof, but it's used in a third-party library and I can't change that part.

When writing lambdas, and casting them, IntelliJ warns me that the casting is redundant, but actually it is needed (it affects the result), and it works if I explicitly declare the lambda. Do you know if this is a bug, maybe I'm missing something or there is a better way to do this?

Example:

public class Main {

    public interface Iface {
        String run();
    }

    public interface IfaceA extends Iface {
    }

    public interface IfaceB extends Iface {
    }

    public static void lambdaTest(Iface iface) {
        System.out.print(iface.run()+": ");
        if (iface instanceof IfaceA) {
            System.out.println("IfaceA");
        } else if (iface instanceof IfaceB) {
            System.out.println("IfaceB");

        } else {
            System.out.println("Iface");

        }
    }

    public static void main(String[] args) {
        lambdaTest((IfaceA)() -> "Casted to A");
        lambdaTest((IfaceB)() -> "Casted to B");
        lambdaTest(() -> "Not Casted");

        IfaceA lambda = () -> "Declared as A";
        lambdaTest(lambda);
    }
}

And the output is:

Casted to A: IfaceA 
Casted to B: IfaceB 
Not Casted: Iface 
Declared as A: IfaceA

But in IntelliJ I get the warning:

Also tested javac and I don't get any warning:

 % javac Main.java -Xlint                                                                                                                                                                          !2525

Answer 1

In Intellij 2016.1.1 (build 145.597 as of March 29th) no warning is shown. You are probably using older version of Idea and the issue was fixed since then.