1. Which is a correct insight about the relationship between reference variables and objects in Java polymorphism?

A. Reference variables can only refer to objects of their exact type, not subtypes B. The reference type decides which methods are callable at compile time C. Objects can change their class at runtime based on the reference type D. Reference variables declared final can be reassigned multiple times

2. When an overridden method exists in a child class, which version is invoked during runtime if the reference variable type is the parent class?

A. Parent class version always B. Child class version always C. Depends on the declared reference type at compile time D. Overridden method is not invoked automatically

3. What keyword is used in a child class to call the overridden method of its parent class?

A. this B. super C. parent D. base

4. Which statement is TRUE about Java objects and the IS-A test in polymorphism?

A. Only child classes pass more than one IS-A test B. All Java objects are polymorphic because they pass the IS-A test for Object class C. An object can pass the IS-A test only for its own type D. IS-A test is irrelevant in Java polymorphism

5. Which of the following declarations is illegal given `Deer d = new Deer();`?

A. Animal a = d; B. Vegetarian v = d; C. Object o = d; D. String s = d;

6. Can the type of a reference variable in Java be changed once declared?

A. Yes, at runtime through casting B. No, it cannot be changed C. Yes, but only for final variables D. Yes, by reassigning to a new object

7. What does it mean to say "a Deer IS-A Object" in the context of polymorphism?

A. Deer is a subclass of Object B. Deer can be referenced only as Object C. Deer inherits methods only from Object D. Object is a subtype of Deer

8. What happens if a subclass does not override a method of its parent class?

A. A compile-time error occurs B. The parent class method is used when called on subclass objects C. Method invocation fails at runtime D. The subclass inherits a static copy of the method

9. How does the Java compiler behave when invoking a method on a reference variable?

A. It always resolves the method to the child class methods B. It verifies the method’s existence in the declared type at compile time C. It ignores the declared type and resolves at runtime only D. It disallows calling methods not present in the actual object’s class

10. What kind of methods are overridden methods in Java considered?

A. Static methods B. Final methods C. Virtual methods D. Native methods

11. In Java polymorphism, what is the significance of the IS-A relationship?

A. It determines the visibility of fields B. It defines whether a class can have multiple constructors C. It checks if an object is considered polymorphic by associating it with parent type(s) D. It allows assignment of primitive types to objects

12. If `Object o = d;` where `d` is a `Deer` object, what methods can be invoked on `o` without casting?

A. Only methods declared in Deer B. Only methods declared in Object C. Methods declared in Animal and Vegetarian D. All methods in Deer, Animal, and Vegetarian

13. Which of the following is NOT true for polymorphism in Java?

A. All Java objects are polymorphic since they inherit from Object B. A reference variable can invoke any method defined in the actual object at runtime C. A reference variable has access only to methods defined by its declared type D. Polymorphism allows objects to be treated as instances of their parent classes

14. In Java polymorphism, what does it mean when a parent class reference is used to refer to a child class object?

A. The parent class object can access child class methods only B. The child class inherits all methods from the parent class C. The reference variable can refer to an object of its declared type or any subtype D. The reference type can be changed dynamically at runtime

15. Which of these statements about polymorphism in Java is FALSE?

A. An object passing multiple IS-A tests signifies polymorphism B. Polymorphism only exists for classes, not interfaces C. A reference variable can be of an interface type and refer to implementing objects D. All Java objects inherit from the Object class

16. What does polymorphism in Java refer to?

A. The ability of a class to inherit from multiple classes B. The ability of an object to take on many forms C. The ability to change the data type of reference variables at run time D. The ability to overload methods within the same class

17. What is the output order for the constructors when creating a new Salary object?

A. Salary constructor then Employee constructor B. Employee constructor then Salary constructor C. Only Salary constructor is called D. Only Employee constructor is called

18. How does Java handle method overriding at run time?

A. It invokes the method defined in the reference variable’s declared class B. It invokes the method defined in the actual object's class C. It throws a compile-time error D. It ignores method overriding and calls parent method always

19. Which concept explains that methods are invoked according to the actual object type, not the reference type?

A. Method overloading B. Virtual method invocation C. Static binding D. Early binding

20. What is a key limitation of a reference variable in Java?

A. It can point to objects of any type whenever needed B. Its data type can be changed after declaration C. It can invoke only those methods defined in its declared type or its supertypes D. It cannot be reassigned if not declared final

21. Given the classes:

A. A Deer IS-A Animal B. A Deer IS-A Vegetarian C. A Deer IS-A Object D. An Animal IS-A Deer

22. If we have: Animal a = new Deer(); Which methods can be invoked on 'a' without casting?

A. Only methods declared in Deer B. Only methods declared in Animal or its supertypes C. Methods only declared in Object D. Methods declared in Vegetarian interface exclusively

23. In method overriding, what happens when the child class uses the super keyword in its overriding method?

A. It hides the parent’s method permanently B. It invokes the parent class’s overridden method C. It disallows the method to be called D. It creates a new method unrelated to the parent method

24. Consider the statements:

A. s.mailCheck() calls Employee’s mailCheck, e.mailCheck() calls Salary’s mailCheck B. Both calls invoke Salary’s mailCheck at runtime C. Both calls invoke Employee’s mailCheck at runtime D. s.mailCheck() cannot be called due to type mismatch

25. What is a virtual method in Java?

A. A method that has no body B. A method that is compiled but not run C. An overridden method whose implementation is determined at run time D. A static method of a class

26. According to the document, what is the implication of declaring a reference variable as final?

A. The object it refers to can be changed B. The reference variable cannot be reassigned to another object C. The object type can change but not the reference type D. The reference variable is shared among all instances

27. Consider:

A. Employee B. Salary C. Both Employee and Salary D. Neither, it causes a compile error

28. Why is mailCheck considered a virtual method in the example?

A. Because it has multiple versions in unrelated classes B. Because it is final and cannot be overridden C. Because it is bound at runtime to the overriding method D. Because it only exists in the parent class

29. What happens when a reference variable method call is validated at compile time but executed at runtime on an overriding method?

A. This indicates a compile-time error B. This is an example of static binding C. This shows dynamic or virtual method invocation D. This is a violation of Java’s type safety

30. What role does the reference variable's declared type play in method invocation?

A. It determines the exact method executed at runtime B. It restricts which methods can be called at compile time C. It has no role in method invocation D. It changes the object’s class

31. What is the output when the `mailCheck` method is called on an `Employee` reference pointing to a `Salary` object?

A. Employee class mailCheck method is invoked B. Salary class mailCheck method is invoked C. Compile-time error D. Method does not exist

32. Why does Java use virtual method invocation?

A. To enhance performance by skipping method lookups B. To allow the invocation of overridden methods at run time C. To prevent subclasses from overriding methods D. To resolve static method calls

33. Is it possible for a Java class to extend multiple classes simultaneously?

A. Yes, multiple inheritance is allowed B. No, Java does not support multiple class inheritance C. Yes, but only if classes are interfaces D. Only abstract classes support multiple inheritance

34. What happens when a final method is overridden?

A. Compilation error B. The subclass method is invoked C. Runtime exception D. The parent method is always invoked

35. Which of the following declarations is NOT legal considering the class hierarchy: Deer extends Animal and implements Vegetarian?

A. Deer d = new Deer(); B. Animal a = new Deer(); C. Vegetarian v = new Deer(); D. String s = new Deer();

36. What is required for a child class to override a parent’s method?

A. The method in the child class must have a different return type B. The method in the child class must have the same signature as the parent’s method C. The method in the child class must be static D. The parent class method must be private

37. In the context of the provided example, what role does the setSalary method play?

A. It overrides a parent class method B. It allows validation of the new salary value before setting it C. It is an abstract method that must be implemented D. It is unused in the Salary class

38. Which is true about the `toString()` method in Java?

A. It cannot be overridden B. It is a method inherited from the Object class C. It is private to each class D. It is static by default

39. Which type of reference variable allows invoking methods on an object in Java?

A. Primitive type variable B. Reference variable of a specific class or interface type C. Static variable D. Instance variable

40. How does Java handle method overriding during compile time?

A. The compiler checks the method in the reference type to validate method calls B. The compiler uses the method in the actual object’s class C. Java does not allow method overriding D. Method overriding is resolved only during compile time

41. What kind of inheritance allows a class to implement multiple interfaces or extend a class and implement interfaces in Java?

A. Multiple inheritance with classes B. Single inheritance only C. Multiple inheritance of type (through interfaces) D. No inheritance is allowed

42. In the polymorphic example, which class does the interface `Vegetarian` represent?

A. A superinterface implemented by Deer B. A parent class of Deer C. The superclass of Animal D. A primitive type

43. Given `public class Salary extends Employee`, which statement is FALSE?

A. Salary inherits methods from Employee B. Salary can override Employee’s methods C. Salary objects cannot be referenced by Employee type variables D. Salary can add new methods and fields

44. Which of the following statements about reference variables in Java is TRUE?

A. Once declared, a reference variable’s type can be changed dynamically during execution B. Reference variables can refer only to objects of the exact declared type C. A reference variable can refer to any subtype object of its declared type D. Reference variables can refer to primitives directly

45. Can a reference variable in Java reference an object of a subtype?

A. Yes, a reference variable of a parent type can refer to objects of its subtype B. No, reference variables can only refer to objects of their own declared type C. Yes, but only if the reference variable is final D. No, unless the object is of primitive type

46. Which is the correct statement about the final keyword with reference variables?

A. final reference variables cannot be reassigned to a different object B. final reference variables can change their object at runtime C. final enforces method overriding D. final reference variables cannot invoke any methods

47. What does the declaration `Animal a = new Deer();` demonstrate?

A. Multiple inheritance B. Upcasting where a subclass object is assigned to a superclass reference C. Downcasting where a superclass reference is assigned to a subclass object D. Reference variable type change

48. Which of the following is an example of method overriding?

A. Defining two methods with the same name but different parameters in the same class B. Defining a method in a subclass with the same signature as a method in the superclass C. Defining a method with the same name in different unrelated classes D. Defining a static method with the same name as an instance method

49. Why does the output show “Within mailCheck of Salary class” when calling mailCheck using an Employee reference variable?

A. Because the method in Employee class forwards the call to Salary B. Because the JVM decides at runtime to invoke the overriding method in the actual object’s class C. Because the compiler treats Employee and Salary references identically D. Because the method in Employee is abstract

50. What does it mean when we say "Overridden method is invoked at runtime no matter the data type of reference"?

A. Method calls are resolved only by the reference type at compile time B. Actual method executed depends on the object's class, not the reference type C. The JVM chooses at random which method to invoke D. Overridden methods cannot be hidden by child classes