What is the primary difference between an abstract class

Solution

o Abstract classes are still classes; they can have constructors, instance variables (fields), and both abstract and concrete methods. They can also contain state. o Interfaces are contracts that define a set of methods that a class must implement. Before Java 8, interfaces could only have abstract methods (and public static final fields). Since Java 8, they can have default and static methods, and since Java 9, private methods. However, interfaces cannot have constructors or instance variables (non-static fields).