java - Error:incompatible types: DeviceCheckCallback is not a functional interface -


i have interface once functional. i'd have more abstract methods added them interface , changed implementations override methods. use retrolambda in project. when run app following error:

error:incompatible types: devicecheckcallback not functional interface multiple non-overriding abstract methods found in interface devicecheckcallback

why seeing this? don't want interface functional anymore?

the interface trying provide lambda has more 1 method. lambda's can used interfaces have single method (which call "functional interface")


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