Lambda methods / default / quirk / bug erase type using ECJ?

Question

I came to this today and spent years trying to reproduce / find out what is happening. Can someone explain why this is happening, or is it a mistake with erase / default methods like / lambda's / polymorphism? Uncommenting the default method makes it work fine, but I expected this to work, as

Conclusion:

Works fine with an object Calling consume Hello Calling accept with context Hello Calling accept via consumer... Exception in thread "main" java.lang.AbstractMethodError: Method test/LambdaTest$$Lambda$1.accept(Ljava/lang/Object;)V is abstract at test.LambdaTest$$Lambda$1/834600351.accept(Unknown Source) at test.LambdaTest.main(LambdaTest.java:24) 

the code

 package test; import java.util.function.Consumer; public class LambdaTest { public static void main(String[] args) { Consumer<Context> contextIgnoringObject = new ContextUnawareObject(); contextIgnoringObject.accept(new Context()); ContextIgnorer contextIgnoringLambda = () -> { System.err.println("Hello"); }; System.err.println("Calling consume"); contextIgnoringLambda.consume(); System.err.println("Calling accept with context"); contextIgnoringLambda.accept(new Context()); Consumer<Context> consumer = contextIgnoringLambda; System.err.println("Calling accept via consumer..."); consumer.accept(new Context()); } @FunctionalInterface public interface ContextIgnorer extends Consumer<Context> { // default void accept(Object object) { // System.err.println("Manual bridge method"); // accept((Context)object); // } @Override default void accept(Context context) { consume(); } void consume(); } public static class ContextUnawareObject implements ContextIgnorer { @Override public void consume() { System.err.println("Works fine with an object"); } } public static class Context { } } 

Answer 1

The problem occurs with the old ECJ compiler (3.10.0):

 $ java -jar org.eclipse.jdt.core-3.10.0.v20140604-1726.jar -source 1.8 LambdaTest.java $ java LambdaTest Works fine with an object Calling consume Hello Calling accept with context Hello Calling accept via consumer... Exception in thread "main" java.lang.AbstractMethodError: Method LambdaTest$$Lambda$1.accept(Ljava/lang/Object;)V is abstract at LambdaTest$$Lambda$1/424058530.accept(Unknown Source) at LambdaTest.main(LambdaTest.java:24) 

Using org.eclipse.jdt.core_3.10.0.v20140902-0626.jar or newer solves the problem. The Oracle javac compiler does not have such a problem. So the solution would be to upgrade your ECJ compiler or go to javac.