I have the following code and javac is not able to select version of the overloaded get() method to use. Why not?
public class x {
static <T> T get(Key<T> key, T defaultValue)
{throw new UnsupportedOperationException();}
static <T> T get(Key<T> key,
java.util.function.Supplier<T> defaultValueSupplier)
{throw new UnsupportedOperationException();}
static void test(){
Key<String> k = new Key<>();
String s = get(k, () -> "test");
}
private static class Key<T>{}
}
When I compile:
% javac -version
javac 1.8.0_202
% javac x.java
x.java:11: error: reference to get is ambiguous
String s = get(k, () -> "test");
^
both method <T#1>get(Key<T#1>,T#1) in x and method <T#2>get(Key<T#2>,Supplier<T#2>) in x match
where T#1,T#2 are type-variables:
T#1 extends Object declared in method <T#1>get(Key<T#1>,T#1)
T#2 extends Object declared in method <T#2>get(Key<T#2>,Supplier<T#2>)
x.java:11: error: incompatible types: cannot infer type-variable(s) T
String s = get(k, () -> "test");
^
(argument mismatch; String is not a functional interface)
where T is a type-variable:
T extends Object declared in method <T>get(Key<T>,T)
2 errors
The error is the same in Java versions 9-12.
My argument is that this line from the error is wrong:
both method <T#1>get(Key<T#1>,T#1) in x and method <T#2>get(Key<T#2>,Supplier<T#2>) in x match
The code does not match method <T#1>get(Key<T#1>,T#1) as k is of type Key<String> and the lambda is certainly not of type String.
If I change the code to:
Key<String> k = new Key<>();
Supplier<String> l = () -> "test";
String s = get(k, l);
then it works. What is causing javac to match the code against both methods?
