Top 250 Java Interview Questions (+Pdf) (2024)

Java Crash Course + Top 250 Interview Questions + Coding Questions (with PDF Book)

What you'll learn

Java Interview Preparation and Crash Course

250 Java Interview Questions and Answers

How to Crack Java Interviews

Java interview guide in PDF format

Requirements

Some basic Java knowledge in advance is good to have

Description

One Stop Destination For All Java Interview Questions and Answers.Top 250 Java Interview Questions and Answers (Video Lectures + Revision PDF Book): (Topics from which  questions are covered)1. Java-Basics2. Variables & Data types3. Operators4. Control statements - Basics5. Control statements - Advanced6. String & StringBuilder7. Arrays8. Classes, Objects & Package9. Access Specifiers, Getter-Setter & this keyword10. Inheritance11. Polymorphism12. Encapsulation & Abstraction13. Abstract class & Interface14. Constructors15. Exception Handling - Basics16. Exception Handling - Advanced17. Collections - Basics18. Collections - Advanced19. Multithreading Overview20. Multithreading Implementation21. Generics - Basics22. Generics - Advanced23. Lambda expression24. Inner class & Final class25. Static class & EnumTop 30 Coding QuestionsMock InterviewsRevision PDF Books: All notes are present in PDF and PPT format in resources of the course.Code: For every question, the code is present in its slide notes of PowerPoint.Interview Preparation Tracker Sheet: All questions listed in this tracker excel. Just have a look just before the interviews.About Instructor: The instructor has more than 15 years of experience in full-stack development and has given and taken more than 100 interviews in his career. He helps candidates in cracking the interviews.All the best for your interview preparation.Remember, NEVER EVER GIVE UP before selection while giving job interviews.

Overview

Section 1: Introduction

Lecture 1 Course Structure and Introduction (PDF books attached in resources)

Section 2: Java-Basics

Lecture 2 Java-Basics Introduction

Lecture 3 Q. What is Java?

Lecture 4 Q. What are JDK, JRE & JVM? How a Java program compiled or executed?

Lecture 5 Q. What is compile-time and run-time in Java?

Lecture 6 Q. What are the main features and advantages of Java?

Lecture 7 Q. How Java is platform independent? Why convert java code to bytecode?

Lecture 8 Q. How to setup VS Code for Java? (not an interview question)

Lecture 9 What is the role of public, static and void in it?

Lecture 10 Q. What is Java Bytecode? What is high-level, low-level code?

Section 3: Variables & Data types

Lecture 11 Variables & Data types

Lecture 12 Q. What are variables & data types? What are the types of data types?

Lecture 13 Q. What are primitive data types?

Lecture 14 Q. What are reference/ non-primitive data types?

Lecture 15 Q. What are the differences between primitive and reference data types?

Section 4: Operators

Lecture 16 Operators Introduction

Lecture 17 Q. What are Operators? What the types of operators in Java?

Lecture 18 Q. What are Arithmetic Operators?

Lecture 19 Q. What are Assignment Operators?

Lecture 20 Q. What are Comparison Operators? When to use them?

Lecture 21 Q. What are Logical Operators? When to use them?

Lecture 22 Q. What are Unary Operators?

Lecture 23 Q. What are Ternary (Conditional) Operators?

Lecture 24 Q. What is instanceOf Operator?

Section 5: Control statements - Basics

Lecture 25 Control statements - Basics - Introduction

Lecture 26 Q. What are control statements in Java?

Lecture 27 Q. What are conditional statements? What is if-elseif-else condition?

Lecture 28 Q. What are looping statements in Java? What is while loop?

Lecture 29 Q. What is the difference between while loop and for loop?

Lecture 30 Q. What is the difference between break and continue statement?

Section 6: Control statements - Advanced

Lecture 31 Control statements - Advanced - Introduction

Lecture 32 Q. What is the difference between while loop and do-while loop?

Lecture 33 Q. How to decide which loop(for, while, do-while) to use in real applications?

Lecture 34 Q. What is the difference btw for loop and for-each loop? When to use for-each l

Lecture 35 Q. What is switch statement?

Lecture 36 Q. When to use which type of conditional statements in real applications?

Section 7: Mock Interview Question and Answers - 1

Lecture 37 Java-Basics, Variables & Data types, Operators, Control statements

Lecture 38 Java-Basics, Variables & Data types, Operators, Control statements

Section 8: String & StringBuilder

Lecture 39 String & StringBuilder - Introduction

Lecture 40 Q. What is StringBuilder? Difference between String and StringBuilder?

Lecture 41 Q. When to use String and when to use StringBuilder in real applications?

Lecture 42 Q. What is the concept of string pool in Java?

Lecture 43 Q. Difference between == and equals() method for comparing strings?

Lecture 44 Q. What are the important methods of String class?

Section 9: Arrays

Lecture 45 Arrays

Lecture 46 Q. What is an Array? Why we need array in real applications?

Lecture 47 Q. How to declare and initialize an array? How to access array elements?

Lecture 48 Q. What is the length property of an array?

Lecture 49 Q. How do you iterate over an array in Java?

Section 10: OOPS - Classes, Objects & Package

Lecture 50 OOPS - Classes, Objects & Package - Introduction

Lecture 51 Q. What is OOPS? What are the main concepts of OOPS?

Lecture 52 Q. What are classes and objects? Why use them in applications?

Lecture 53 Q. How to implement classes and objects in Java?

Lecture 54 Q. What are the members of class?

Lecture 55 Q. What is the role and benefit of package in Java?

Section 11: OOPS - Access Specifiers, Getter-Setter & this keyword

Lecture 56 OOPS - Access Specifiers, Getter-Setter & this keyword

Lecture 57 Q. What are access specifiers? What are public and private specifiers?

Lecture 58 Q. What is the role of default access specifier? Difference btw public, private

Lecture 59 Q. What is the role of this keyword in java? When to use it?

Lecture 60 Q. Why to use same names for class fields and parameter name in Setter method?

Lecture 61 Q. What are getter and setter methods?

Lecture 62 Q. What are the advantages of getter and setter methods?

Lecture 63 Q. What are the 4 principles/ pillars of OOPS?

Section 12: Mock Interview Question and Answers - 2

Lecture 64 OOPS - Classes, Objects, Access Specifiers, Getter-Setter & this keyword

Lecture 65 OOPS - Classes, Objects, Access Specifiers, Getter-Setter & this keyword

Section 13: OOPS - Inheritance

Lecture 66 OOPS - Inheritance - Introduction

Lecture 67 Q. What is inheritance and when to use inheritance in real applications?

Lecture 68 Q. How to implement inheritance in Java?

Lecture 69 Q. What are the different types of Inheritance? When to use what?

Lecture 70 Q. What is multiple inheritance? Does Java support it?

Lecture 71 Q. Why Java does not support multiple inheritance of classes?

Lecture 72 Q. What is the alternative of multiple inheritance in Java?

Lecture 73 Q. How to prevent a class from being inherited?

Section 14: OOPS - Polymorphism

Lecture 74 OOPS - Polymorphism - Introduction

Lecture 75 Q. What is polymorphism?

Lecture 76 Q. What are the types of polymorphism?

Lecture 77 Q. What is Method Overloading? How to implement it and when to use it?

Lecture 78 Q. Why do we call method overloading as a type of compile-time or early binding?

Lecture 79 Q. In how many ways can a method be overloaded?

Lecture 80 Q. If two same methods have different return type, then are methods are overload

Lecture 81 Q. What is Method Overriding?

Lecture 82 Q. Why to use method overriding? Why don’t we have different name methods?

Lecture 83 Q. How to implement method overriding?

Lecture 84 Q. Why we call method overriding as a run-time or late binding?

Lecture 85 Q. What are the 5 differences between Overloading and Overriding?

Lecture 86 Q. What are Annotations in Java?

Section 15: OOPS - Encapsulation & Abstraction

Lecture 87 OOPS - Encapsulation & Abstraction - Introduction

Lecture 88 Q. What is Encapsulation?

Lecture 89 Q. How to achieve Encapsulation in Java?

Lecture 90 Q. What are the advantages of Encapsulation in Java?

Lecture 91 Q. What is Abstraction? How to implement abstraction?

Lecture 92 Q. What is the difference between abstraction and encapsulation?

Section 16: Mock Interview Question and Answers - 3

Lecture 93 OOPS - Inheritance, Polymorphism, Encapsulation & Abstraction

Lecture 94 OOPS - Inheritance, Polymorphism, Encapsulation & Abstraction

Section 17: Abstract class & Interface

Lecture 95 Abstract class & Interface - Introduction

Lecture 96 Q. What is abstract class In Java? How to implement it?

Lecture 97 Q. When to use abstract class in real applications?

Lecture 98 Q. What are interfaces in Java? How to implement it?

Lecture 99 Q. When to use interfaces in real applications?

Lecture 100 Q. Differences between an Abstract class & an Interface ?

Lecture 101 Q. What are default methods? When to use default methods?

Lecture 102 Q. Can you create an instance of an Abstract class or an Interface?

Lecture 103 Q. Do abstract class can have Constructors? What is the use of that constructor?

Lecture 104 Q. Do Interface can have a constructor?

Lecture 105 Q. When to use Interface and when Abstract class in real applications?

Lecture 106 Q. How to achieve abstraction? Abstraction vs Abstract class ?

Section 18: Constructors

Lecture 107 Constructors - Introduction

Lecture 108 Q. What is Constructor in Java?

Lecture 109 Q. What are the types of constructors? What is Default constructor?

Lecture 110 Q. What is Parameterized constructor? When to use it in real applications?

Lecture 111 Q. What is constructor overloading? When to use it in real applications?

Lecture 112 Q. What is constructor chaining?

Lecture 113 Q. What is copy constructor?

Lecture 114 Q. When to use copy constructor in real applications?

Lecture 115 Q. Can a constructor have a return type?

Lecture 116 Q. What will happen if no constructor is defined inside the class?

Lecture 117 Q. What is the role of super keyword?

Section 19: Mock Interview Question and Answers - 4

Lecture 118 Abstract class & Interface, Constructors

Lecture 119 Abstract class & Interface, Constructors

Section 20: Exception Handling - Basics

Lecture 120 Exception Handling - Basics - Introduction

Lecture 121 Q. What is Exception Handling? How to implement it in Java?

Lecture 122 Q. What is the role of finally in exception handling?

Lecture 123 Q. When to use finally in real applications?

Lecture 124 Q. Can we have multiple catch blocks ?

Lecture 125 Q. What is catch-all block? Is it a good practice in real applications?

Lecture 126 Q. Can we execute all catch blocks at one time?

Section 21: Exception Handling - Advanced

Lecture 127 Exception Handling - Advanced - Introduction

Lecture 128 Q. What is the role of throw keyword in exception handling? When to use it?

Lecture 129 Q. What is the role of throws keyword in exception handling?

Lecture 130 Q. What are the differences between throw and throws keywords?

Lecture 131 Q. What are the types of exceptions in Java?

Lecture 132 Q. What are checked and unchecked exceptions?

Section 22: Mock Interview Question and Answers - 5

Lecture 133 Exception Handling

Lecture 134 Exception Handling

Section 23: Collections - Basics

Lecture 135 Collections - Basics - Introduction

Lecture 136 Q. What are collections and what is their use in Java?

Lecture 137 Q. What are the types of collections in Java?

Lecture 138 Q. What are Iterable & Collection interfaces?

Lecture 139 Q. What are List, Queue & Set collections? What is the difference between them?

Lecture 140 Q. What is Arraylist? How to implement it and when to use it?

Lecture 141 Q. What are the differences between Array and Arraylist?

Lecture 142 Q. What is HashSet? What are the differences btw ArrayList(List) & HashSet(Set)?

Lecture 143 Q. What is Map In Java? Which classes implements Map interface?

Lecture 144 Q. What is HashMap In Java? How to implement it and when to use it?

Lecture 145 Q. What are the differences btw HashSet(Set) and HashMap(Map)?

Section 24: Collections - Advanced

Lecture 146 Collections - Advanced - Introduction

Lecture 147 Q. What is LinkedList in Java? What are Singly and Doubly linked list?

Lecture 148 Q. How to implement LinkedList? Difference between Arraylist & LinkedList?

Lecture 149 Q. What are Collections?

Lecture 150 Q. What is TreeSet in Java? What is the difference between HashSet and TreeSet?

Lecture 151 Q. What is the difference between HashMap and HashTable?

Lecture 152 Q. What are the advantages of using collections?

Section 25: Mock Interview Question and Answers - 6

Lecture 153 Collections

Lecture 154 Collections

Section 26: Multithreading - Overview

Lecture 155 Multithreading - Overview - Introduction

Lecture 156 Q. What is Process and Thread? What is the difference between them?

Lecture 157 Q. Explain Multithreading? What is the advantage of it?

Lecture 158 Q. What is Main Thread & Daemon Thread in Java?

Section 27: Multithreading - Implementation

Lecture 159 Multithreading - Implementation

Lecture 160 Q. In how many ways we can implement multithreading in Java?

Lecture 161 Q. How to implement multithreading using Thread class?

Lecture 162 Q. How to implement multithreading using Runnable Interface?

Lecture 163 Q. What is the differences between Thread class & Runnable interface?

Lecture 164 Q. What are some important methods of Thread class?

Section 28: Mock Interview Question and Answers - 7

Lecture 165 Multithreading

Lecture 166 Multithreading

Section 29: Generics - Basics

Lecture 167 Generics - Basics - Introduction

Lecture 168 Q. What is the role of Generics in Java?

Lecture 169 Q. What is a Generic method? How to implement Generic method?

Lecture 170 Q. What is a Generic class? How to implement Generic class?

Lecture 171 Q. What are type parameters and type arguments? What is T in Generic class?

Lecture 172 Q. When to use Generic method and when to use Generic class in Java?

Section 30: Generics - Advanced

Lecture 173 Generics - Advanced - Introduction

Lecture 174 Q. What are bounded type parameters in generics?

Lecture 175 Q. Can primitive types be used as type arguments in generics?

Lecture 176 Q. How to use Generics with Collections?

Lecture 177 Q. What is Type Safety? How generics provide type safety?

Lecture 178 Q. What is Type casting? How generics eliminates type casting?

Lecture 179 Q. What are the advantages of using Generics?

Section 31: Mock Interview Question and Answers - 8

Lecture 180 Generics

Lecture 181 Generics

Section 32: Lambda expression

Lecture 182 Lambda expression - Introduction

Lecture 183 Q. What is lambda expression and lambda operator?

Lecture 184 Q. What is the difference between normal interface and functional interface?

Lecture 185 Q. How to use lambda expression to implement functional interfaces?

Lecture 186 Q. Can we use lambda expression for non-functional interfaces?

Section 33: Types of Classes - Inner class & Final class

Lecture 187 Types of Classes - Inner class & Final class - Introduction

Lecture 188 Q. What are the types of classes in Java?

Lecture 189 Q. What are Inner Classes (Nested Classes)?

Lecture 190 Q. What is Final class in Java?

Lecture 191 Q. What is Final method in Java?

Lecture 192 Q. What is the role of final keyword?

Section 34: Types of Classes - Static class & Enum

Lecture 193 Types of Classes - Static class & Enum

Lecture 194 Q. What is the role of Static method?

Lecture 195 Q. When to use static methods in real applications?

Lecture 196 Q. What is Static nested class?

Lecture 197 Q. What is the role of static keyword in Java?

Lecture 198 Q. What is Enum? What is the use of it in real applications?

Lecture 199 Q. How to use and implement Enums?

Section 35: Mock Interview Question and Answers - 9

Lecture 200 Types of Classes

Lecture 201 Types of Classes

Section 36: Coding Question and Answers

Lecture 202 Array Coding Problems

Lecture 203 Q. What are the must-know pre-requisites for solving basic coding problems?

Lecture 204 Q. What is the common approach for solving coding problems?

Lecture 205 Q. Write a function to calculate the sum of all elements in an array.

Lecture 206 Q. Write a function to calculate the average of an array of numbers.

Lecture 207 Q. Write a function to find the smallest number in an array.

Lecture 208 Q. Write a function to find the largest number in an array.

Lecture 209 Q. Write a function to find the second largest number in an array.

Section 37: Array Coding Problems Using Functions

Lecture 210 Array Coding Problems Using Functions

Lecture 211 Q. What are the top 5 important array functions used in coding problems?

Lecture 212 Q. Write a function to check whether two arrays are same or not?

Lecture 213 Q. Function to check if a given array is sorted in ascending order or Not?

Lecture 214 Q. Write a function to merge two arrays into a single sorted array.

Lecture 215 Q. Write a function to remove a specific element from an array.

Section 38: String Coding Problems

Lecture 216 String Coding Problems

Lecture 217 Q. Write a function that counts the number of characters in a string?

Lecture 218 Q. How to iterate a string?

Lecture 219 Q. Write a function that returns the reverse of a string?

Lecture 220 Q. Write a function that checks whether a given string is a palindrome or not?

Section 39: String Coding Problems Using Functions

Lecture 221 String Coding Problems Using Functions

Lecture 222 Q. What are the important methods of String class?

Lecture 223 Q. What are some more important methods of String class?

Lecture 224 Q. Write a function that returns the longest word in the sentence.

Lecture 225 Q. Write a function to remove all whitespace characters from a string.

Lecture 226 Q. Write a function that counts the number of vowels in a string?

Lecture 227 Q. Write a function that checks whether two strings are anagrams or not?

Section 40: Number Coding Problems

Lecture 228 Number Coding Problems

Lecture 229 Q. Write a function to calculate the factorial of a number.

Lecture 230 Q. What is the difference between ++i and i++?

Lecture 231 Q. Write a function that checks whether a number is prime or not?

Lecture 232 Q. How to swap two numbers in Java?

Lecture 233 Q. Write a function to calculate the GCD for two numbers.

Lecture 234 Q. Write a function to sum the digits of a number.

Lecture 235 Q. Write a function to calculate the Fibonacci sequence up to a given number.

Section 41: Coding Algorithms

Lecture 236 Coding Algorithms

Lecture 237 Q. Write a function to sort an array of numbers in ascending order(Bubble Sort).

Lecture 238 Q. Write a function to search an element in any array(Binary Search)?

Lecture 239 End

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