0. OOP

Question 1

What is Object Oriented Programming (OOP)?

Answer 1

Object Oriented Programming (OOP) is a programming paradigm based on the concept of ‘objects’, which can contain data in the form of fields and code in the form of procedures or methods.

Question 2

What are the four main principles of OOP?

Answer 2

The four main principles of OOP are Encapsulation, Abstraction, Inheritance, and Polymorphism.

Question 3

What is encapsulation in OOP?

Answer 3

Encapsulation is the principle of bundling the data (attributes) and methods (functions) that operate on the data into a single unit, or class, and restricting access to some of the object’s components.

Question 4

True or False: In Java, encapsulation is achieved using access modifiers.

Answer 4

True.

Question 5

What is abstraction in OOP?

Answer 5

Abstraction is the principle of hiding the complex implementation details of a system and exposing only the necessary features to the user.

Question 6

How does inheritance work in Java?

Answer 6

Inheritance allows a new class (subclass) to inherit properties and methods from an existing class (superclass), enabling code reusability and the creation of hierarchical relationships between classes.

Question 7

Fill in the blank: In Java, a class that is inherited from is called a __________.

Answer 7

superclass.

Question 8

What is polymorphism in OOP?

Answer 8

Polymorphism is the ability of different classes to be treated as instances of the same class through a common interface, allowing methods to perform differently based on the object that it is acting upon.

Question 9

What is a class in Java?

Answer 9

A class in Java is a blueprint for creating objects that defines a set of attributes and methods that the created objects will have.

Question 10

What is an object in Java?

Answer 10

An object is an instance of a class, containing specific values for the attributes defined in the class.

Question 11

What are access modifiers in Java?

Answer 11

Access modifiers are keywords that set the accessibility levels for classes, methods, and variables. The main access modifiers in Java are public, private, protected, and default.

Question 12

What does the ‘private’ access modifier do?

Answer 12

‘Private’ restricts the visibility of a class member to within the class itself, making it inaccessible from outside the class.

Question 13

What is a constructor in Java?

Answer 13

A constructor is a special method used to initialize objects. It has the same name as the class and does not have a return type.

Question 14

True or False: A Java class can have multiple constructors.

Answer 14

True.

Question 15

What is method overloading in Java?

Answer 15

Method overloading is a feature that allows a class to have more than one method with the same name but different parameters (different type or number of parameters).

Question 16

What is method overriding in Java?

Answer 16

Method overriding occurs when a subclass provides a specific implementation of a method that is already defined in its superclass.

Question 17

What is the purpose of the ‘super’ keyword?

Answer 17

The ‘super’ keyword is used to refer to the superclass of the current object and can be used to call superclass methods and constructors.

Question 18

What is an interface in Java?

Answer 18

An interface in Java is a reference type similar to a class that can contain only constants, method signatures, default methods, static methods, and nested types. Interfaces cannot contain instance fields or constructors.

Question 19

Fill in the blank: A class can implement multiple __________ in Java.

Answer 19

interfaces.

Question 20

What is an abstract class in Java?

Answer 20

An abstract class is a class that cannot be instantiated and may contain abstract methods, which are methods without a body that must be implemented by subclasses.

Question 21

True or False: An abstract class can have both abstract and concrete methods.

Answer 21

True.

Question 22

What is the difference between an interface and an abstract class?

Answer 22

An interface can only contain method signatures and constants, whereas an abstract class can contain both abstract methods and concrete methods, along with instance variables.

Question 23

What is a package in Java?

Answer 23

A package in Java is a namespace that organizes a set of related classes and interfaces, helping to avoid naming conflicts and controlling access.

Question 24

What is the main purpose of the Java Collections Framework?

Answer 24

The Java Collections Framework provides a set of classes and interfaces for storing and manipulating groups of data as a single unit, offering efficient ways to handle collections of objects.

Question 25

What is a List in Java?

Answer 25

A List is an ordered collection that can contain duplicate elements. It allows positional access and insertion of elements.

Question 26

What is a Set in Java?

Answer 26

A Set is a collection that does not allow duplicate elements and does not guarantee any specific order of its elements.

Question 27

What is a Map in Java?

Answer 27

A Map is an object that maps keys to values, where each key is unique and is used to retrieve the corresponding value.

Question 28

What is the difference between ArrayList and LinkedList?

Answer 28

ArrayList is backed by a dynamic array and provides fast random access, while LinkedList is backed by a doubly linked list and provides faster insertion and deletion.

Question 29

What is exception handling in Java?

Answer 29

Exception handling in Java is a mechanism to handle runtime errors, allowing the program to continue execution rather than crashing.

Question 30

What are the keywords used for exception handling in Java?

Answer 30

The keywords used for exception handling in Java are try, catch, finally, throw, and throws.

Question 31

What is the purpose of the 'try' block?

Answer 31

The 'try' block is used to wrap code that may throw an exception, allowing the program to attempt execution of that code.

Question 32

What is the purpose of the 'catch' block?

Answer 32

The 'catch' block is used to handle the exception that is thrown in the corresponding 'try' block, providing a way to respond to the error.

Question 33

What is the difference between checked and unchecked exceptions?

Answer 33

Checked exceptions are exceptions that must be either caught or declared in the method signature, while unchecked exceptions do not have this requirement and are typically programming errors.

Question 34

What is the Java Virtual Machine (JVM)?

Answer 34

The Java Virtual Machine (JVM) is an abstract computing machine that enables a computer to run Java programs by converting Java bytecode into machine language.

Question 35

What is the Java Development Kit (JDK)?

Answer 35

The Java Development Kit (JDK) is a software development kit that includes tools for developing, debugging, and monitoring Java applications, including the Java Runtime Environment (JRE) and development tools such as the Java compiler.

Question 36

What is the Java Runtime Environment (JRE)?

Answer 36

The Java Runtime Environment (JRE) is a part of the JDK that provides the libraries, Java Virtual Machine (JVM), and other components necessary to run Java applications.

Question 37

What is a thread in Java?

Answer 37

A thread in Java is a lightweight process that enables concurrent execution of two or more parts of a program for maximum utilization of CPU.

Question 38

What is synchronization in Java?

Answer 38

Synchronization is a mechanism that ensures that two or more concurrent threads do not simultaneously execute some particular program segment, preventing data inconsistency.

Question 39

What is the purpose of the 'volatile' keyword?

Answer 39

The 'volatile' keyword in Java is used to indicate that a variable's value will be modified by different threads, ensuring visibility of changes to variables across threads.

Question 40

What is the difference between 'final', 'finally', and 'finalize' in Java?

Answer 40

'final' is a keyword used to declare constants, 'finally' is a block that executes after a try-catch block regardless of whether an exception was thrown, and 'finalize' is a method that is called by the garbage collector before an object is removed from memory.

Question 41

What is garbage collection in Java?

Answer 41

Garbage collection in Java is the process by which the Java Virtual Machine automatically deletes unreferenced objects, freeing up memory and improving performance.

Question 42

What is a lambda expression in Java?

Answer 42

A lambda expression in Java is a concise way to represent an anonymous function that can be passed around, allowing for functional programming capabilities.

Question 43

True or False: Lambda expressions can only be used with functional interfaces.

Answer 43

True.

Question 44

What is a functional interface in Java?

Answer 44

A functional interface in Java is an interface that contains exactly one abstract method, which can be implemented using a lambda expression.

Question 45

What does 'this' keyword refer to in Java?

Answer 45

The 'this' keyword in Java refers to the current instance of the class, allowing access to class attributes and methods.

Question 46

What is the purpose of the 'instanceof' operator?

Answer 46

'instanceof' is used to test whether an object is an instance of a specific class or interface.

Question 47

What is the significance of the 'transient' keyword?

Answer 47

The 'transient' keyword in Java is used to indicate that a field should not be serialized when the object is converted to a byte stream.

Question 48

What is method reference in Java?

Answer 48

Method reference is a shorthand notation of a lambda expression to call a method, providing a way to refer to methods without executing them.

Question 49

What is a stream in Java?

Answer 49

A stream in Java is a sequence of elements that can be processed in a functional style, allowing for operations such as filter, map, and reduce.

Question 50

What is the difference between a shallow copy and a deep copy?

Answer 50

A shallow copy creates a new object but copies references to the original object's data, while a deep copy creates a new object and also recursively copies all objects referenced by the original object.

Question 51

What are the main benefits of using OOP?

Answer 51

The main benefits of using OOP include code reusability, scalability, easier maintenance, and better organization of complex programs.

Question 52

What is the role of the 'default' keyword in interfaces?

Answer 52

The 'default' keyword allows the definition of a default implementation for methods in an interface, enabling backward compatibility.

Question 53

What is the significance of the 'static' keyword in a class?

Answer 53

The 'static' keyword indicates that a member belongs to the class, rather than instances of the class, allowing access to that member without creating an object.

Question 54

What is a nested class in Java?

Answer 54

A nested class is a class defined within another class, which can access the members of the enclosing class, including private members.

Question 55

What is the purpose of the 'static import' feature?

Answer 55

The 'static import' feature allows members (fields and methods) of a class to be accessed without class qualification, improving code readability.

Question 56

What is the 'main' method in Java?

Answer 56

The 'main' method is the entry point of any standalone Java application, defined as 'public static void main(String[] args)'.

Question 57

How can you create an immutable class in Java?

Answer 57

To create an immutable class in Java, declare the class as final, make all fields private and final, and provide no setters, initializing fields via a constructor.