Java Interview Guide : 200+ Interview Questions and Answers
Java Interview Guide : 200+ Interview Questions and Answers

Java Interview Guide : 200+ Interview Questions and Answers

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Hours of Content: 6

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 a 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?

Who is the target audience?

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

Java Interview Guide : 200+ Interview Questions and Answers

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