Abstract classes and interfaces in Java serve fundamentally different purposes ... so it depends on an implementation to serve its purpose. An interface can never have a state, so it cannot ...

The release of Java SE 15 ... page for a sealed class.) A hierarchy like Shape gives its clients a choice: they can deal with shapes entirely through their abstract interface, but they also ...

To further confuse matters, every Java collection class that implements the List interface does have a size() method. Classes including Vector, Stack and ArrayList all have a size method. So to get ...