The following code will produce the red squiggly under the implementing class name ONLY AFTER A PROJECT -> CLEAN (which is another problem). Even with the red line, if you go to Source -> Override/Implement Methods the methods that are abstract in the abstract class are not shown.

import org.aopalliance.intercept.MethodInterceptor

class MethodInterceptorImp extends MethodInterceptor{

}

Source -> Override/Implement Methods produces

Select methods to override or implement:

Object
clone()
equals(Object)
finalize()
hasCode()
toString()

In this particular case the abstract method, Object invoke(MethodInvocation invocation) throws Throwable;, is missing in the options.

While this code specifically implements a Java abstract class I can duplicate the problem with Scala traits.