'this' is a reference to the current object instance, while 'super' is a reference to the parent class. They serve different purposes in inheritance hierarchy.

The 'final' keyword when applied to a variable makes it a constant. When applied to a class, it cannot be extended. When applied to a method, it cannot be overridden.

Java supports only single class inheritance to avoid the diamond problem. However, multiple interface implementation is allowed.

This demonstrates runtime polymorphism. Although the reference is of type Parent, the actual object is Child. The overridden show() method in Child class is executed.

Java achieves runtime polymorphism through method overriding using inheritance. Unlike C++, Java doesn't use the 'virtual' keyword; it's implicit for all non-final methods.

Interfaces cannot be instantiated directly. You must create a concrete class that implements the interface or use an anonymous inner class.

The default (package-private) access modifier allows access to members from any class within the same package, but not from classes in other packages.

Encapsulation is the bundling of data (variables) and methods into a single unit (class) while hiding the internal implementation details from the outside world. It is achieved using access modifiers.

Method overloading is compile-time (static) polymorphism with same method name but different parameters in the same class. Method overriding is runtime (dynamic) polymorphism where a child class provides a specific implementation of a parent method.

Dog inherits the concrete method sleep() from Animal and provides implementation for the abstract method sound(). Therefore, Dog objects can call both methods.