Java Class and Object Quiz

Which of the following best describes a class in Java?

• A runtime entity

• A blueprint for objects

• An instance of an object

• A collection of libraries

Answer explanation

Answer: B – a blueprint for objects
Explanation: A class acts as a template that defines variables and methods used to create objects.

What is an object in Java?

• A compiled file

• A set of instructions

• An instance of a class

• A variable

Answer explanation

Answer: C – an instance of a class
Explanation: Objects are specific instances created using a class, representing real-world entities.

What keyword is used to create an object in Java?

• this

• new

• object

• create

Answer explanation

Answer: B – new
Explanation: The new keyword allocates memory and creates a new object of a class.

Which of the following is NOT a benefit of using classes and objects?

• Encourages code reuse

• Promotes modularity

• Forces linear programming

• Simplifies maintenance

Answer explanation

Answer: C – Forces linear programming
Explanation: OOP supports modular and scalable programming, not linear procedural code.

Which of the following is a correct example of a class structure in Java?

• class A { void A(); }

• public static class A() {}

• class A { int x; void show() {} }

• object A {}

Answer explanation

Answer: C – class A { int x; void show() {} }
Explanation: This defines a class with a variable and method — the correct structure in Java.

What happens to instance variables when multiple objects are created from the same class?

• Shared among all objects

• Exist only in main()

• Each object gets its own copy

• Stored in static memory

Answer explanation

Answer: C – Each object gets its own copy
Explanation: Instance variables are unique for every object created from the class.

Given the class Student, how do you create an object of it?

• Student();

• Student obj = new Student();

• object Student = new();

• new Student();

Answer explanation

Answer: B – Student obj = new Student();
Explanation: This is the correct syntax using the new keyword to instantiate an object.

What are the main components of a class in Java?

• Title, Body, Conclusion

• Name, Attributes, Loop

• Class name, Variables, Methods, Constructor

• Object, Function, Reference

Answer explanation

Answer: C – Class name, Variables, Methods, Constructor
Explanation: A class consists of a name, attributes (variables), methods, and optionally constructors.

In the class diagram below, what does - name: String indicate?

• Public method

• Private variable

• Static method

• Public class

Answer explanation

Answer: B – Private variable
Explanation: In UML, - denotes a private attribute; + denotes public.

Which concept allows code reuse in object-oriented programming?

• Loops

• Inheritance

• Object instantiation

• Garbage Collection

Answer explanation

Answer: C – Object instantiation
Explanation: By creating multiple objects from one class, we reuse the same structure/code.