When you implement an interface method (by overriding the interface’s method header), remember that all of the methods whose headers are declared in the interface are implicitly declared public.

See the Java 101 Java interfaces tutorial for a more in-depth introduction to using interfaces in your Java programs, including where and where not to use default, static, and private methods.

That’s all you really need to know about the java.util.function.Function interface. It is a very simple component that simply requires the implementation of one method — named apply — that is passed ...

There is a reason why Java method modifiers exist. ... And an implementation public class CreateOrderServiceImpl implements ... You could potentially create an interface method with the same signature ...