Udemy Java Interview Guide : 200+ Interview Questions and Answers Udemy
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    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?
    Updated on 14 September, 2016
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