Conclusion: The biggest difference between abstract and non abstract method is that abstract methods can either be hidden or overridden, but non abstract methods can only be hidden. And that abstract methods don't have an implementation, not even an empty pair of curly braces.

What are abstract methods?

An abstract method is a method that is declared without an implementation (without braces, and followed by a semicolon), like this: abstract void moveTo(double deltaX, double deltaY);

What is abstract and non abstract methods in Java?

An abstract class can extend only one class or one abstract class at a time. Declaring a class as abstract with no abstract methods means that we don't allow it to be instantiated on its own. An abstract class used in Java signifies that we can't create an object of the class directly.