Java Object-Oriented Principles Quiz

1. What is abstraction in Java?

• The process of exposing essential information while hiding unnecessary detail.
• The technique of allowing multiple methods with the same name.
• The method of combining data and methods into a single unit.
• The way of creating new class hierarchies from existing ones.

2. What is encapsulation in Java?

• The process of exposing essential information while hiding unnecessary detail.
• The ability of an object to take on multiple forms, depending on the context.
• A class that cannot be instantiated directly and serves as a base class.
• The practice of bundling data and methods that operate on that data into a single unit, typically a class.

3. What is inheritance in Java?

• The ability to execute code in random order.
• The mechanism for hiding data from other classes.
• The creation of multiple classes with the same name.
• The process by which a new class adopts the properties of another class.

4. What is polymorphism in Java?

• A method for encapsulating functionalities within a single class.
• The practice of hiding data to protect it from outside access.
• The ability of an object to take on multiple forms, depending on the context in which it is used.
• The process of converting an object into a string format.

5. What is an abstract class in Java?

• A class that does not contain any methods or properties.
• A class that can be instantiated and used directly.
• A class that only contains static methods and variables.
• A class that cannot be instantiated directly and serves as a base class for other classes to inherit.

6. What is an interface in Java?

• A type of variable that can hold multiple values.
• A keyword that specifies the visibility of a class member.
• A contract that defines a set of methods that must be implemented by any class that implements it.
• A method that cannot be overridden by subclasses.

7. How do you declare an abstract method in Java?

• By using the final keyword before the method declaration.
• By using the static keyword before the method declaration.
• By using the abstract keyword before the method declaration.
• By using the synchronized keyword before the method declaration.

8. How do you declare an interface in Java?

• By using the class keyword followed by the name of the interface.
• By using the abstract keyword followed by the name of the interface.
• By using the interface keyword followed by the name of the interface.
• By using the public keyword followed by the name of the interface.

9. What is method overriding in Java?

• The process of creating multiple methods with the same name in a single class.
• The act of preventing a superclass from being altered in a subclass.
• The implementation of a method in an abstract class only.
• The ability of a subclass to provide a specific implementation of a method that is already provided by its superclass.

10. What is method overloading in Java?

• The ability to use multiple subclasses in a class hierarchy.
• The process of creating new classes from existing classes.
• A way to define classes without any methods.
• The ability of a class to have multiple methods with the same name but different parameters.

11. How do you define a class in Java?

• By using the struct keyword followed by the name of the class.
• By using the class keyword followed by the name of the class.
• By using the object keyword followed by the name of the class.
• By using the define keyword followed by the name of the class.

12. What is the purpose of getters and setters in encapsulation?

• To automatically update all variables every time they are accessed.
• To control access to internal data by providing methods to get and set the values of private variables.
• To eliminate the need for private variables in a class.
• To directly manipulate internal variables without restrictions.

13. How do you create an instance of a class in Java?

• By using the new keyword followed by the name of the class.
• By using the create keyword followed by the class name.
• By using the instantiate keyword followed by the class name.
• By using the define keyword followed by the class name.

14. What is the difference between a superclass and a subclass in Java?

• A superclass is the parent class, while a subclass is the child class that inherits properties from the superclass.
• A superclass is the child class, while a subclass is the parent class that it inherits from.
• A superclass is an interface, while a subclass is a class that implements it.
• A superclass is a class that cannot be subclassed, while a subclass is a class that can be.

15. How do you extend a class in Java?

• By using the extends keyword followed by the name of the superclass.
• By using the implements keyword followed by the name of the superclass.
• By using the inherits keyword followed by the name of the superclass.
• By using the super keyword followed by the name of the superclass.

16. What is upcasting in Java?

• The technique of copying the properties of a subclass to a superclass.
• The practice of creating multiple instances of a class.
• The process of assigning a subclass object to a superclass reference variable.
• The method of converting a superclass object into a subclass.

17. What is downcasting in Java?

• The method of declaring a variable with a specific type.
• The act of creating an object from a class.
• The process of converting a string into a number.
• The process of assigning a superclass object to a subclass reference variable.

18. How do you handle exceptions in Java?

• By using try-catch blocks to catch and handle exceptions.
• By using if-else statements to skip errors.
• By using loops to retry the operation automatically.
• By writing all code in a single method without checks.

19. What is the purpose of the finally block in exception handling?

• To handle an exception if it is thrown during execution.
• To catch multiple exceptions in a single block of code.
• To ensure that certain code is executed regardless of whether an exception is thrown or not.
• To define the behavior of the program in case of a runtime failure.

20. How do you implement polymorphism using method overriding?

• By using the static keyword in the method declaration.
• By providing a specific implementation of a method in a subclass that is already provided by its superclass.
• By adding parameters to the overridden method in the subclass.
• By creating multiple methods with the same name in a subclass.

21. How do you implement polymorphism using method overloading?

• By having methods with the same parameters but different return types.
• By using different class names for methods with the same functionality.
• By providing multiple methods with the same name but different parameters in a class.
• By creating one method that accepts all types of parameters.

22. What is the difference between static and instance variables in Java?

• Both static and instance variables are shared equally among all instances.
• Static variables are unique for each instance of a class, while instance variables are shared.
• Static variables are shared by all instances of a class, while instance variables are unique to each instance of a class.
• Instance variables can only be accessed from static methods, but static variables cannot.

23. How do you declare a static method in Java?

• By using the public keyword before the method declaration.
• By using the void keyword before the method declaration.
• By using the static keyword before the method declaration.
• By using the final keyword before the method declaration.

24. What is the purpose of the toString method in Java?

• To serialize an object for storage.
• To convert an object to a byte array.
• To provide a string representation of an object.
• To clone an object into a new instance.

25. How do you override the toString method in a class?

• By using the toString method in the main function only.
• By declaring the toString method as static in the class.
• By providing a specific implementation of the toString method in a subclass.
• By removing the toString method from the class entirely.

26. What is the purpose of the equals method in Java?

• To retrieve object properties.
• To compare two objects for equality.
• To create new object instances.
• To assign values to variables.

27. How do you override the equals method in a class?

• By ignoring the method in the subclass entirely.
• By creating a new method with a different name.
• By using the equals keyword before the method declaration.
• By providing a specific implementation of the equals method in a subclass.

28. What is the purpose of the hashCode method in Java?

• To print the object details in a human-readable format.
• To provide a unique integer value for an object, which is used in hash-based collections like HashMap and HashSet.
• To encrypt data for secure storage in applications.
• To evaluate conditions for exception handling in the program.

29. How do you override the hashCode method in a class?

• By defining a hashCode method without a return type.
• By using the final keyword before the hashCode method.
• By providing a specific implementation of the hashCode method in a subclass.
• By using the override keyword before the hashCode method.

30. What is the difference between a constructor and a method in Java?

• A constructor is an abstract class that cannot be instantiated, while a method is a variable that holds data.
• A constructor is a special method that is called when an object is created, while a method is a block of code that performs a specific action.
• A constructor defines a class, while a method is a feature of an interface.
• A constructor is a type of loop used in programming, while a method is a function that returns a value.