Java Interview Guide: 200+ Questions & Answers

Java Interview Guide 200+ Interview Questions and Answers

A Beginners Guide to Java Interview with 200+ Java Interview Questions

Created by : Rated :4.2 75261 views

Last Updated: 2024-11-21 07:11:46 English Course Type: Self Learning

Understand what kind of questions are asked in Beginner Java Interviews
Answer questions on Java Platform, Wrapper Classes and Strings
Understand New Features of Java
Understand Basic Object Oriented Concepts
Understand Advanced Object Oriented Concepts
Answer questions on Collections, Generics and MultiThreading
Understand New Features in Java 5, Java 6, Java 7 and Java 8
Understand basics of Functional Programming - Lambda Expressions and Streams
Understand Exception Handling Best Practices

Course Description

Preparing for Java Interview is tricky. You would need to get a good understanding of new features and revise concepts you used in your preparation. This course helps you prepare for Java Interview with hands-on code examples covering 200+ Java Interview Questions and Answers on varied range of topics listed below.

Java Platform

1 . Why is Java so popular?
2 . What is platform independence?
3 . What is bytecode?
4 . Compare JDK vs JVM vs JRE
5 . What are the important differences between C++ and Java?
6 . What is the role for a classloader in Java?

Wrapper Classes

7 . What are Wrapper classes?
8 . Why do we need Wrapper classes in Java?
9 . What are the different ways of creating Wrapper class instances?
10 . What are differences in the two ways of creating Wrapper classes?
11 . What is auto boxing?
12 . What are the advantages of auto boxing?
13 . What is casting?
14 . What is implicit casting?
15 . What is explicit casting?

Strings

16 . Are all String’s immutable?
17 . Where are String values stored in memory?
18 . Why should you be careful about String concatenation(+) operator in loops?
19 . How do you solve above problem?
20 . What are differences between String and StringBuffer?
21 . What are differences between StringBuilder and StringBuffer?
22 . Can you give examples of different utility methods in String class?

Object oriented programming basics

23 . What is a class?
24 . What is an object?
25 . What is state of an object?
26 . What is behavior of an object?
27 . What is the super class of every class in Java?
28 . Explain about toString method ?
29 . What is the use of equals method in Java?
30 . What are the important things to consider when implementing equals method?
31 . What is the Hashcode method used for in Java?
32 . Explain inheritance with examples .
33 . What is method overloading?
34 . What is method overriding?
35 . Can super class reference variable can hold an object of sub class?
36 . Is multiple inheritance allowed in Java?
37 . What is an interface?
38 . How do you define an interface?
39 . How do you implement an interface?
40 . Can you explain a few tricky things about interfaces?
41 . Can you extend an interface?
42 . Can a class extend multiple interfaces?
43 . What is an abstract class?
44 . When do you use an abstract class?
45 . How do you define an abstract method?
46 . Compare abstract class vs interface?
47 . What is a constructor?
48 . What is a default constructor?
49 . Will this code compile?
50 . How do you call a super class constructor from a constructor?
51 . Will this code compile?
52 . What is the use of this()?
53 . Can a constructor be called directly from a method?
54 . Is a super class constructor called even when there is no explicit call from a sub class constructor?

Advanced object oriented concepts

55 . What is polymorphism?
56 . What is the use of instanceof operator in Java?
57 . What is coupling?
58 . What is cohesion?
59 . What is encapsulation?
60 . What is an inner class?
61 . What is a static inner class?
62 . Can you create an inner class inside a method?
63 . What is an anonymous class?

Modifiers

64 . What is default class modifier?
65 . What is private access modifier?
66 . What is default or package access modifier?
67 . What is protected access modifier?
68 . What is public access modifier?
69 . What access types of variables can be accessed from a class in same package?
70 . What access types of variables can be accessed from a class in different package?
71 . What access types of variables can be accessed from a sub class in same package?
72 . What access types of variables can be accessed from a sub class in different package?
73 . What is the use of a final modifier on a class?
74 . What is the use of a final modifier on a method?
75 . What is a final variable?
76 . What is a final argument?
77 . What happens when a variable is marked as volatile?
78 . What is a static variable?

conditions & loops

79 . Why should you always use blocks around if statement?
80 . Guess the output
81 . Guess the output
82 . Guess the output of this switch block .
83 . Guess the output of this switch block?
84 . Should default be the last case in a switch statement?
85 . Can a switch statement be used around a String
86 . Guess the output of this for loop
87 . What is an enhanced for loop?
88 . What is the output of the for loop below?
89 . What is the output of the program below?
90 . What is the output of the program below?

Exception handling

91 . Why is exception handling important?
92 . What design pattern is used to implement exception handling features in most languages?
93 . What is the need for finally block?
94 . In what scenarios is code in finally not executed?
95 . Will finally be executed in the program below?
96 . Is try without a catch is allowed?
97 . Is try without catch and finally allowed?
98 . Can you explain the hierarchy of exception handling classes?
99 . What is the difference between error and exception?
100 . What is the difference between checked exceptions and unchecked exceptions?
101 . How do you throw an exception from a method?
102 . What happens when you throw a checked exception from a method?
103 . What are the options you have to eliminate compilation errors when handling checked exceptions?
104 . How do you create a custom exception?
105 . How do you handle multiple exception types with same exception handling block?
106 . Can you explain about try with resources?
107 . How does try with resources work?
108 . Can you explain a few exception handling best practices?

Miscellaneous topics

109 . What are the default values in an array?
110 . How do you loop around an array using enhanced for loop?
111 . How do you print the content of an array?
112 . How do you compare two arrays?
113 . What is an enum?
114 . Can you use a switch statement around an enum?
115 . What are variable arguments or varargs?
116 . What are asserts used for?
117 . When should asserts be used?
118 . What is garbage collection?
119 . Can you explain garbage collection with an example?
120 . When is garbage collection run?
121 . What are best practices on garbage collection?
122 . What are initialization blocks?
123 . What is a static initializer?
124 . What is an instance initializer block?
125 . What is tokenizing?
126 . Can you give an example of tokenizing?
127 . What is serialization?
128 . How do you serialize an object using serializable interface?
129 . How do you de-serialize in Java?
130 . What do you do if only parts of the object have to be serialized?
131 . How do you serialize a hierarchy of objects?
132 . Are the constructors in an object invoked when it is de-serialized?
133 . Are the values of static variables stored when an object is serialized?

Collections

134 . Why do we need collections in Java?
135 . What are the important interfaces in the collection hierarchy?
136 . What are the important methods that are declared in the collection interface?
137 . Can you explain briefly about the List interface?
138 . Explain about ArrayList with an example?
139 . Can an ArrayList have duplicate elements?
140 . How do you iterate around an ArrayList using iterator?
141 . How do you sort an ArrayList?
142 . How do you sort elements in an ArrayList using comparable interface?
143 . How do you sort elements in an ArrayList using comparator interface?
144 . What is vector class? How is it different from an ArrayList?
145 . What is linkedList? What interfaces does it implement? How is it different from an ArrayList?
146 . Can you briefly explain about the Set interface?
147 . What are the important interfaces related to the Set interface?
148 . What is the difference between Set and sortedSet interfaces?
149 . Can you give examples of classes that implement the Set interface?
150 . What is a HashSet?
151 . What is a linkedHashSet? How is different from a HashSet?
152 . What is a TreeSet? How is different from a HashSet?
153 . Can you give examples of implementations of navigableSet?
154 . Explain briefly about Queue interface?
155 . What are the important interfaces related to the Queue interface?
156 . Explain about the Deque interface?
157 . Explain the BlockingQueue interface?
158 . What is a priorityQueue?
159 . Can you give example implementations of the BlockingQueue interface?
160 . Can you briefly explain about the Map interface?
161 . What is difference between Map and sortedMap?
162 . What is a HashMap?
163 . What are the different methods in a Hash Map?
164 . What is a TreeMap? How is different from a HashMap?
165 . Can you give an example of implementation of navigableMap interface?
166 . What are the static methods present in the collections class?

Advanced collections

167 . What is the difference between synchronized and concurrent collections in Java?
168 . Explain about the new concurrent collections in Java?
169 . Explain about copyonwrite concurrent collections approach?
170 . What is compareandswap approach?
171 . What is a lock? How is it different from using synchronized approach?
172 . What is initial capacity of a Java collection?
173 . What is load factor?
174 . When does a Java collection throw UnsupportedOperationException?
175 . What is difference between fail-safe and fail-fast iterators?
176 . What are atomic operations in Java?
177 . What is BlockingQueue in Java?

Generics

178 . What are Generics?
179 . Why do we need Generics? Can you give an example of how Generics make a program more flexible?
180 . How do you declare a generic class?
181 . What are the restrictions in using generic type that is declared in a class declaration?
182 . How can we restrict Generics to a subclass of particular class?
183 . How can we restrict Generics to a super class of particular class?
184 . Can you give an example of a generic method?

Multi threading

185 . What is the need for threads in Java?
186 . How do you create a thread?
187 . How do you create a thread by extending thread class?
188 . How do you create a thread by implementing runnable interface?
189 . How do you run a thread in Java?
190 . What are the different states of a thread?
191 . What is priority of a thread? How do you change the priority of a thread?
192 . What is executorservice?
193 . Can you give an example for executorservice?
194 . Explain different ways of creating executor services .
195 . How do you check whether an executionservice task executed successfully?
196 . What is callable? How do you execute a callable from executionservice?
197 . What is synchronization of threads?
198 . Can you give an example of a synchronized block?
199 . Can a static method be synchronized?
200 . What is the use of join method in threads?
201 . Describe a few other important methods in threads?
202 . What is a deadlock?
203 . What are the important methods in Java for inter-thread communication?
204 . What is the use of wait method?
205 . What is the use of notify method?
206 . What is the use of notifyall method?
207 . Can you write a synchronized program with wait and notify methods?

Functional Programming - Lamdba expressions and Streams

208 . What is functional programming?
209 . Can you give an example of functional programming?
210 . What is a stream?
211 . Explain about streams with an example?
what are intermediate operations in streams?
212 . What are terminal operations in streams?
213 . What are method references?
214 . What are lambda expressions?
215 . Can you give an example of lambda expression?
216 . Can you explain the relationship between lambda expression and functional interfaces?
217 . What is a predicate?
218 . What is the functional interface - function?
219 . What is a consumer?
220 . Can you give examples of functional interfaces with multiple arguments?

New Features

221 . What are the new features in Java 5?
222 . What are the new features in Java 6?
223 . What are the new features in Java 7?
224 What are the new features in Java 8?

Familiarity with Java and any Java IDE
In the course, we use Eclipse to demonstrate examples. Some Java IDE will be useful.
Access to Github Repository

Students who are learning Java
Students who are planning to attend Java Interviews
Students who want to add more depth to their Java Knowledge

Section 1 : Introduction to Course 4 Lectures 00:05:17
Lecture 1 :
Introduction Preview
Lecture 2 :
Three Things You need to Know
Lecture 3 :
Java Interview Questions
Lecture 4 :
Course Overview
Section 2 : Java Platform 4 Lectures 00:15:19
Lecture 1 :
Java Popularity and Platform Independence
Lecture 2 :
Compare JDK vs JVM vs JRE
Lecture 3 :
Differences between C++ and Java
Lecture 4 :
Java Classloaders
Section 3 : Wrapper Classes 1 Lectures 00:11:01
Lecture 1 :
Wrapper Classes
Section 4 : Strings 1 Lectures 00:09:46
Lecture 1 :
String, StringBuffer and StringBuilder
Section 5 : Basics of Object Oriented Programming 8 Lectures 00:59:29
Lecture 1 :
Object Basics - Class, Object, State and Behavior
Lecture 2 :
ToString method
Lecture 3 :
Equals and hashCode methods
Lecture 4 :
Inheritance, Method overloading and Method overriding
Lecture 5 :
Interface
Lecture 6 :
Abstract Class
Lecture 7 :
Constructors - this() and super()
Lecture 8 :
Do not forget to do Exercises
Section 6 : More Object Oriented Programming Concepts 6 Lectures 00:32:13
Lecture 1 :
What is Coupling?
Lecture 2 :
What is Cohesion?
Lecture 3 :
What is Encapsulation?
Lecture 4 :
Inner Class and Static Inner Class
Lecture 5 :
What is an anonymous class?
Lecture 6 :
Polymorphism and instanceof
Section 7 : Modifiers 3 Lectures 00:20:38
Lecture 1 :
Access Modifiers - public, private, protected and default
Lecture 2 :
Final method, variable and class
Lecture 3 :
Static variables and methods
Section 8 : Conditions and Loops 1 Lectures 00:08:09
Lecture 1 :
Simple Puzzles on conditions and loops
Section 9 : Exception Handling 4 Lectures 00:32:00
Lecture 1 :
Exception Handling - try, catch and finally
Lecture 2 :
Checked and Unchecked Exceptions
Lecture 3 :
Throwing an Exception
Lecture 4 :
Creating Custom Exceptions
Section 10 : Miscellaneous Topics 6 Lectures 00:31:16
Lecture 1 :
Arrays
Lecture 2 :
Enum
Lecture 3 :
Variable Arguments
Lecture 4 :
Asserts and Garbage Collection
Lecture 5 :
Static and Member Initializers
Lecture 6 :
Serialization
Section 11 : Collections 6 Lectures 00:43:20
Lecture 1 :
Collection Interface Hierarchy
Lecture 2 :
Collection & List Interface methods and classes - ArrayList, Vector & LinkedList
Lecture 3 :
Set interfaces and implementations - HashSet, LinkedHashSet and TreeSet
Lecture 4 :
Map interfaces and implementations - HashMap, LinkedHashMap and TreeMap
Lecture 5 :
Queue interfaces and implementations - Deque and BlockingQueue
Lecture 6 :
Collection Code Examples
Section 12 : Concurrent Collections 2 Lectures 00:17:42
Lecture 1 :
Concurrent Collections - CopyOnWriteArrayList
Lecture 2 :
CompareAndSwap, Locks and AtomicOperations
Section 13 : Generics 1 Lectures 00:05:23
Lecture 1 :
Generics
Section 14 : Multithreading 3 Lectures 00:24:40
Lecture 1 :
MultiThreading - Need for Threads and Creating Threads
Lecture 2 :
Thread states, priority, ExecutorService and Callable
Lecture 3 :
Synchronization of Threads. join, wait, notify and notifyAll methods
Section 15 : Functional Programming - Lamdba Expressions and Streams 2 Lectures 00:27:31
Lecture 1 :
Functional Programming Examples - Streams and Lambda Expressions
Lecture 2 :
Functional Programming Questions and Answers
Section 16 : New Features 1 Lectures 00:07:48
Lecture 1 :
Java New Features - Java 5, 6, 7 and 8
Section 17 : Thank You!! 1 Lectures 00:01:34
Lecture 1 :
Conclusion

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Ranga Rao,

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I'm Ranga Karanam, an Architect with 15 Years of Java programming and design with major banking clients across the world. We started in28Minutes with the aim to create Hands-on Courses with Real World Projects. Step-By-Step series of Courses is one of our creations. About in28Minutes We use Problem-Solution based Step-By-Step Hands-on Approach With Practical, Real World Application Examples. While our primary expertise is on Programming, Development, Design & Architecture of Java & Related Frameworks (Spring, Spring Boot, Spring MVC, Struts, Hibernate) we are expanding into the front-end world (Bootstrap, Query, Angular JS) and the amazing world of Python Programming and Automation Testing with Selenium Web Driver.