Java Oops Quiz
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Object-oriented programming (OOP) is a fundamental paradigm in Java, enabling the creation of modular, reusable, and maintainable code. This Java OOP quiz delves into the core principles of Java OOP, challenging your understanding of abstraction, encapsulation, inheritance, and polymorphism.
In this quiz, you will encounter questions that assess your knowledge of classes, objects, constructors, access modifiers, interfaces, abstract classes, and method overriding and overloading. This is your opportunity to demonstrate your grasp of these essential concepts and showcase your ability to apply them effectively in Java programming. This quiz offers an invaluable opportunity to expand your knowledge and improve Read moreyour programming abilities.
Java OOPs Questions and Answers
- 1.
What is the primary purpose of inheritance in Java?
- A.
Code reusability
- B.
Data hiding
- C.
Access control
- D.
Memory management
Correct Answer
A. Code reusabilityExplanation
Inheritance in Java allows a new class (subclass) to inherit properties and behaviors (fields and methods) from an existing class (superclass). This promotes code reusability by avoiding code duplication. Subclasses can also add their own unique features or modify inherited behaviors, making the code more adaptable and organized.Rate this question:
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- 2.
Which principle allows objects of different classes to be treated as objects of a common type?
- A.
Abstraction
- B.
Encapsulation
- C.
Polymorphism
- D.
Inheritance
Correct Answer
C. PolymorpHismExplanation
Polymorphism, meaning "many forms," allows objects of different classes to be treated as objects of a common type. This is achieved through method overriding, where a subclass provides a specific implementation for a method already defined in its superclass. At runtime, the appropriate method is called based on the actual object's class.Rate this question:
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- 3.
What is the role of a constructor in a Java class?
- A.
Define class methods
- B.
Declare class variables
- C.
Initialize object state
- D.
Control access to members
Correct Answer
C. Initialize object stateExplanation
A constructor is a special method with the same name as the class. It is automatically called when a new object of that class is created. Its primary role is to initialize the object's fields, ensuring that the object starts in a valid and usable state.Rate this question:
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- 4.
Which access modifier restricts access to a class member to within the same class only?
- A.
Public
- B.
Protected
- C.
Private
- D.
Default
Correct Answer
C. PrivateExplanation
The private access modifier is the most restrictive access level in Java. It limits access to a class member (field or method) to within the same class only. This enforces encapsulation by preventing external code from directly accessing or modifying the internal data of an object.Rate this question:
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- 5.
What is the keyword used to declare an interface in Java?
- A.
Interface
- B.
Class
- C.
Abstract
- D.
Extends
Correct Answer
A. InterfaceExplanation
An interface in Java is a contract that defines a set of methods that implementing classes must provide. It specifies the behaviors that classes should exhibit but doesn't provide the implementation details. Interfaces promote abstraction and flexibility in code design.Rate this question:
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- 6.
Can an abstract class have non-abstract methods?
- A.
Yes
- B.
No
- C.
Only if it has abstract methods
- D.
Only if it inherits from another abstract class
Correct Answer
A. YesExplanation
An abstract class can have both abstract and non-abstract methods. Abstract methods are declared without an implementation, acting as placeholders for subclasses to provide concrete implementations. Non-abstract methods have complete implementations and can be used directly by the abstract class or its subclasses.Rate this question:
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- 7.
What is the difference between method overriding and method overloading?
- A.
Overriding changes method signature, overloading doesn't
- B.
Overloading changes method signature, overriding doesn't
- C.
Overriding provides a new implementation, overloading provides multiple methods with the same name
- D.
They are the same
Correct Answer
C. Overriding provides a new implementation, overloading provides multiple methods with the same nameExplanation
Method overriding involves providing a specific implementation for a method that is already defined in a superclass. This allows subclasses to customize inherited behaviors. Method overloading, on the other hand, involves defining multiple methods with the same name but different parameters in the same class.Rate this question:
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- 8.
What is the purpose of the this keyword in Java?
- A.
Refer to the current class
- B.
Refer to the parent class
- C.
Refer to the current object
- D.
Refer to a static method
Correct Answer
C. Refer to the current objectExplanation
The this keyword in Java refers to the current object within a non-static method or constructor. It's used to differentiate between instance variables and local variables or method parameters when they have the same name. It can also be used to call other constructors within the same class.Rate this question:
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- 9.
What is the difference between an abstract class and an interface?
- A.
An abstract class can have constructors, an interface cannot
- B.
An interface can have constructors, an abstract class cannot
- C.
An abstract class can be instantiated, an interface cannot
- D.
An interface can be instantiated, an abstract class cannot
Correct Answer
A. An abstract class can have constructors, an interface cannotExplanation
An abstract class can have constructors, while an interface cannot. Constructors are used to initialize the state of an object when it's created. Since interfaces cannot be instantiated directly, they don't have constructors. Abstract classes, however, can be used as base classes for inheritance.Rate this question:
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- 10.
What is the purpose of encapsulation in Java?
- A.
Improve code readability
- B.
Increase code complexity
- C.
Protect data integrity
- D.
Optimize program performance
Correct Answer
C. Protect data integrityExplanation
Encapsulation is the practice of bundling data (fields) and the methods that operate on that data within a class. It restricts direct access to the data from outside the class, forcing interaction through defined methods. This protects data integrity and promotes modularity.Rate this question:
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Oct 04, 2024Quiz Edited by
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Expert Reviewed by
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Dec 02, 2011Quiz Created by
Srividya A
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