Java Programming Interview Guide : 200+ Questions & Answers

How about Quickly Revising all the Important Java Concepts in about 6 Hours before an interview?

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. 

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COURSE HIGHLIGHTS:

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?

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