Description Lukas Eder 2021-11-25 07:02:12 EST

The following code snippet implements an enum lookup by some enum property:

// -----------------------------------------------------------------------
package p;

import static java.util.function.Function.identity;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Lookup {

    private static final Map<Class<?>, Map<String, I>> LOOKUP = new ConcurrentHashMap<>();

    @SuppressWarnings("unchecked")
    static <E extends Enum<E> & I> E lookupLiteral(Class<E> enumType, String literal) {
        return (E) LOOKUP.computeIfAbsent(enumType, t ->
            Stream.of(enumType.getEnumConstants()).collect(Collectors.<E, String, I>toMap(E::getLiteral, identity()))
        ).get(literal);
    }

    public static void main(String[] args) {
        System.out.println(Lookup.lookupLiteral(X.class, "a"));
    }

    interface I {
        String getLiteral();
    }

    enum X implements I {
        A("a");

        final String literal;

        X(String literal) {
            this.literal = literal;
        }

        @Override
        public String getLiteral() {
            return literal;
        }
    }
}
// -----------------------------------------------------------------------

It runs fine on JDK 17:

// -----------------------------------------------------------------------
$ java -version
openjdk version "17" 2021-09-14
OpenJDK Runtime Environment (build 17+35-2724)
OpenJDK 64-Bit Server VM (build 17+35-2724, mixed mode, sharing)

$ java p/Lookup.java
A
// -----------------------------------------------------------------------

However, when I'm using Eclipse to compile this code, I'm getting the following error at runtime:

// -----------------------------------------------------------------------
Exception in thread "main" java.lang.BootstrapMethodError: bootstrap method initialization exception
	at java.base/java.lang.invoke.BootstrapMethodInvoker.invoke(BootstrapMethodInvoker.java:188)
	at java.base/java.lang.invoke.CallSite.makeSite(CallSite.java:315)
	at java.base/java.lang.invoke.MethodHandleNatives.linkCallSiteImpl(MethodHandleNatives.java:281)
	at java.base/java.lang.invoke.MethodHandleNatives.linkCallSite(MethodHandleNatives.java:271)
	at x/p.Lookup.lambda$0(Lookup.java:17)
	at java.base/java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1708)
	at x/p.Lookup.lookupLiteral(Lookup.java:16)
	at x/p.Lookup.main(Lookup.java:22)
Caused by: java.lang.invoke.LambdaConversionException: Invalid receiver type class java.lang.Enum; not a subtype of implementation type interface p.Lookup$I
	at java.base/java.lang.invoke.AbstractValidatingLambdaMetafactory.validateMetafactoryArgs(AbstractValidatingLambdaMetafactory.java:271)
	at java.base/java.lang.invoke.LambdaMetafactory.metafactory(LambdaMetafactory.java:340)
	at java.base/java.lang.invoke.BootstrapMethodInvoker.invoke(BootstrapMethodInvoker.java:134)
	... 7 more
// -----------------------------------------------------------------------

There used to be a similar bug in javac, which seems to have been fixed by now:
https://bugs.openjdk.java.net/browse/JDK-8141508