Why does a lambda change overloads when it throws a runtime exception?

Question

Bear with me, the introduction is a bit long-winded but this is an interesting puzzle.

I have this code:

public class Testcase {
    public static void m         


        

Answer 1

It appears that when throwing an Exception, the compiler chooses the interface which returns a reference.

interface Calls {
    void add(Runnable run);

    void add(IntSupplier supplier);
}

// Ambiguous call
calls.add(() -> {
        System.out.println("hi");
        throw new IllegalArgumentException();
    });

However

interface Calls {
    void add(Runnable run);

    void add(IntSupplier supplier);

    void add(Supplier supplier);
}

complains

Error:(24, 14) java: reference to add is ambiguous both method add(java.util.function.IntSupplier) in Main.Calls and method add(java.util.function.Supplier) in Main.Calls match

Lastly

interface Calls {
    void add(Runnable run);

    void add(Supplier supplier);
}

compiles fine.

So weirdly;

• void vs int is ambiguous
• int vs Integer is ambiguous
• void vs Integer is NOT ambiguous.

So I figure something is broken here.

I have sent a bug report to oracle.