Object-Oriented Programming

Polymorphism allows one interface to represent a general class of actions, where specific implementations can vary while the interface remains consistent. This is a core OOP principle enabling flexible, reusable code.

Method overloading occurs when a class has multiple methods with the same name but different parameter lists (different number, type, or order of parameters). This allows the same method name to perform different actions based on input.

The this() keyword is used to call another constructor in the same class, enabling constructor chaining. It must be the first statement in a constructor and helps avoid code duplication when multiple constructors share common initialization logic.

Classes defined within other classes, including nested classes or local classes inside methods, are collectively referred to as inner classes. Subclasses inherit from parent classes, and private classes refer to access visibility.

The Cloneable interface is a marker interface that contains NO methods. It indicates that a class permits cloning - the actual clone() method is inherited from Object class. Marker interfaces exist for type-safety and compiler checks only.

Wrapper classes in Java (Integer, Double, Character, Boolean, etc.) encapsulate primitive data types within objects. This allows primitives to be used in contexts requiring objects, such as collections. Super classes and sub classes refer to inheritance relationships, not primitive wrapping.

The Integer wrapper class extends the abstract Number class, which is part of Java's type hierarchy for numeric types. Void does not extend Class (Void is final). Float extends Number, not Double. System does not extend Runtime. Only the Integer-Number relationship is correct.

Constructors are special methods in Java used to initialize the instance variables of an object when it is created. Destructors or garbage collection handle destroying variables, so option b is incorrect.

A valid applet declaration must be a public class that extends java.applet.Applet (or javax.swing.JApplet for Swing). Option B correctly declares 'Public class MyApplet extends java.applet.Applet' (assuming 'Public' is a typo for 'public'). Option A incorrectly uses 'abstract', option C incorrectly uses 'implements', and option D incorrectly combines 'extends applet' (should be 'extends java.applet.Applet') with 'implements Runnable'.

An abstract method declares a method signature without implementation. It ends with a semicolon and has no body (no braces). Option C shows the correct syntax with semicolon and no braces.

A final method cannot be overridden in subclasses. This enforces that the implementation remains unchanged throughout the inheritance hierarchy. However, final methods can still be inherited and called by subclasses.

In Caché ObjectScript, %SerialObject is the base class for serial objects - objects that can be serialized but don't have independent storage. This is the correct inheritance for creating a serial class.

In Caché ObjectScript, %classes refer to system classes - classes starting with % are provided by the system. User-defined classes don't use the % prefix. The claimed answer A (System) is correct.