Are there any reasons to have an abstract class with every method in the class defined?

Question

It seems that an abstract class means the definition of the class is not complete and hence cannot be instantiated.

And I saw some simple Java code which has an abstract

Answer 1

You can have an abstract class that implements several interfaces. You need not implement these methods in an abstract class, but you do need to implement them in a subclass of your abstract class.

E.g.

public interface MyInterface{
    void hello();
}

public abstract class Clazzy implements MyInterface {
//I need not have the interface method.
}

public class MySubclass extends Clazzy {

    @Override
    public void hello() {
        // I need to be here
    }

}