If you use the java keyword abstract you cannot provide an implementation.
Sometimes this idea comes from having a background in C++ and mistaking the virtual keyword in C++ as being "almost the same" as the abstract keyword in Java.
In C++ virtual indicates that a method can be overridden and polymorphism will follow, but abstract in Java is not the same thing. In Java abstract is more like a pure virtual method, or one where the implementation must be provided by a subclass. Since Java supports polymorphism without the need to declare it, all methods are virtual from a C++ point of view. So if you want to provide a method that might be overridden, just write it as a "normal" method.
Now to protect a method from being overridden, Java uses the keyword final in coordination with the method declaration to indicate that subclasses cannot override the method.