Problem

Passing a lambda expression or method reference for AnnoyingRunnable or AnnoyingRunner to shh has an issue with the following error.

Ambiguos method call. Both shh(AnnoyingRunnable) in AnnoyingFuns and shh(AnnoyingRunner) in AnnoyingFuns match.

Both AnnoyingRunnable and AnnoyingRunner have SAM with exactly the same method signature so the compiler can't figure out the given lambda expression to method reference is for which FunctionalInterface type.

from j8plus.

Solution

The problem described above has been solved by using Liskov substitution principle.

Before

• Runner wasn't a sub-type of Runnable
• AnnoyingRunner wasn't a sub-type of AnnoyingRunnable
• There is a shh method taking AnnoyingRunnable and then returns Runnable.
• There is a shh method taking AnnoyingRunner and then returns Runner.

After

• Runner is a sub-type of Runnable.
• AnnoyingRunner is a sub-type of AnnoyingRunnable.
• There is only one shh method which takes AnnoyingRunnable then returns Runner.

from j8plus.