Search Interview Questions

Ans. Class using which only immutable (objects that cannot be changed after initialization) objects can be created.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops immutable immutability immutable immutability class string class basic interview question Asked in 18 Companies Basic frequent}

Q92. Difference between object instantiation and construction ?

Ans. Though It's often confused with each other, Object Creation ( Instantiation ) and Initialization ( Construction ) are different things in Java. Construction follows object creation.

Object Creation is the process to create the object in memory and returning its handler. Java provides New keyword for object creation.

Initialization is the process of setting the initial / default values to the members. Constructor is used for this purpose. If we don't provide any constructor, Java provides one default implementation to set the default values according to the member data types.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops constructor object instantiation}

Frequently asked to fresh graduates and less experienced.

Q93. Which of the following is tightly bound ? Inheritance or Composition ?

Ans. Inheritance.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve inheritance object oriented programming (oops) oops concepts java oops composition object oriented programming (oops) oops concepts Asked in 1 Companies basic frequent}

Very frequently asked in phone and walk in interviews.

Q94. What are Marker Interfaces ? Name few Java marker interfaces ?

Ans. An interface without any method declaration is called as marker interface. there are 3 in-built interfaces in JVM i.e. serializable, clonable, remote

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops interfaces marker interface serializable clonable Asked in 21 Companies intermediate frequent}

Frequently asked to fresh graduates.

Q95. Difference between Process and Thread ?

Operating System

Ans. Process is a program in execution whereas thread is a separate path of execution in a program.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java threads multi threading operating system process vs thread Asked in 24 Companies basic frequent}

Very frequently asked. Usually difference between String,StringBuffer and StringBuilder is asked in different variations.

Q96. Difference between StringBuffer and StringBuilder ?

Ans. StringBuffer is synchronized whereas StringBuilder is not.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java string stringbuffer string class stringbuilder synchronized basic interview question infosys technologies Asked in 17 Companies basic frequent}

Q97. Explain java.lang.OutOfMemoryError ?

Ans. This Error is thrown when the Java Virtual Machine cannot allocate an object because it is out of memory, and no more memory could be made available by the garbage collector.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java exceptions jvm outofmemoryerror Asked in 1 Companies}

Q98. Should we override finalize method ?

Ans. Finalize is used by Java for Garbage collection. It should not be done as we should leave the Garbage Collection to Java itself.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java garbage collection java memory management finalize}

Q99. Difference between Builder and Composite ?

Ans. Builder is a creational Design Pattern whereas Composite is a structural design pattern. Composite creates Parent - Child relations between your objects while Builder is used to create group of objects of predefined types.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java design pattern builder composite creational design pattern structural design pattern}

Q100. Difference between Factory and Strategy Design Pattern ?

Design

Ans. Factory is a creational design pattern whereas Strategy is behavioral design pattern. Factory revolves around the creation of object at runtime whereas Strategy or Policy revolves around the decision at runtime.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java design pattern factory strategy creational design pattern behavioral design pattern Asked in 1 Companies expert}

Q101. What is reflection ?

Ans. It is the process of examining / modifying the behaviour of an object at runtime.

Sample Code for reflection

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java reflection reflection api ebay mindtree Asked in 29 Companies basic frequent}

Q102. When do you get ClassCastException?

or

What is ClassCastException ?

Ans. As we only downcast class in the hierarchy, The ClassCastException is thrown to indicate that code has attempted to cast an object to a subclass of which it is not an instance.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops class casting classcastexception exception error Asked in 4 Companies intermediate frequent}

Q103. What are strong, soft, weak and phantom references in Java ?

Ans. Garbage Collector wont remove a strong reference.

A soft reference will only get removed if memory is low.

A weak reference will get removed on the next garbage collection cycle.

A phantom reference will be finalized but the memory will not be reclaimed. Can be useful when you want to be notified that an object is about to be collected.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java memory management jvm garbage collections references strong reference soft reference weak reference phantom reference architecture Asked in 2 Companies}

Q104. What is race condition ?

Operating System

Ans. A source of possible errors in parallel programming, where one thread can cause an error in another thread by changing some aspect of the state of the program that the second thread is depending on (such as the value of variable).

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java.threads multithreading race condition parallel programming synchronization ebay concurrency Asked in 10 Companies}

Q105. What are the Disadvantages of using Collection Classes over Arrays ?

Ans. Collections can only hold objects, It can't hold primitive data types.

Collections have performance overheads as they deal with objects and offer dynamic memory expansion. This dynamic expansion could be a bigger overhead if the collection class needs consecutive memory location like Vectors.

Collections doesn't allow modification while traversal as it may lead to concurrentModificationException.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections collections classes disadvantages of collections over arrays collections vs arrays}

Q106. What is Generalization and Specialization in terms of casting ?

Ans. Generalization or UpCasting is a phenomenon where a sub class is prompted to a super class, and hence becomes more general. Generalization needs widening or up-casting. Specialization or DownCasting is a phenomenon where a super class is narrowed down to a sub class. Specialization needs narrowing or down-casting.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java data types casting type casting up casting type casting downcasting type casting generalization specialization Asked in 2 Companies}

Q107. Can we call the garbage collector explicitly ?

Ans. Yes, We can call garbage collector directly but it doesn't guarantees that the gc will start executing immediately. This gc( ) method appears in both Runtime and System classes of java.lang package.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java garbage collection java memory management jvm gc yes no Asked in 4 Companies expert}

Q108. What will be the output of following code ?

public static void main(String[] args){
String parent = null;
File file = new File(parent, "myfile.txt");
try {
file.createNewFile();
} catch (IOException e) {
e.printStackTrace();
}
}

Ans. It will create the file myfile.txt in the current directory.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java io file fileio coding code file handling}

Q109. What is comparator interface used for ?

Ans. The purpose of comparator interface is to compare objects of the same class to identify the sorting order. Sorted Collection Classes ( TreeSet, TreeMap ) have been designed such to look for this method to identify the sorting order, that is why class need to implement Comparator interface to qualify its objects to be part of Sorted Collections.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections treemap treeset comparator Asked in 2 Companies Intermediate}

Q110. If I try to add Enum constants to a TreeSet, What sorting order will it use ?

Ans. Tree Set will sort the Values in the order in which Enum constants are declared.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections set treeset enum sorting technical lead}

Q111. Can we override compareTo method for Enumerations ?

Ans. No. compareTo method is declared final for the Enumerations and hence cannot be overriden. This has been intentionally done so that one cannot temper with the sorting order on the Enumeration which is the order in which Enum constants are declared.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java compareto final methods enum enumeration expert}

Q112. If you are given a choice to implement the code to either Insert a Record or Update if already exist, Which approach will you follow ?

1. Insert into the DB Table. If exception occurs, update the existing record.
2. Check if the record exists and update it if it exists, If not insert a new record.

Solution

Ans. In first case, there would be 2 DB calls in worst case and 1 in best case. In 2nd approach there will be always 2 DB calls.

Decision on the approach should depend on the following considerations -

1. How costly is the call to DB ? Are we using indices , hibernate etc

If calls to DB are costly , 1st approach should be the choice.

2. Exception Book keeping load upon exception.

The benefit of saving 1st call in approach 1 should be bigger than the Book keeping for the exception.

3. Probability of the exception in first apparoach.

If the DB Table is almost empty, it makes sense to follow Approach 1 as majority of the 1st calls will pass through without exception.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve database insert-update db exceution plan db strategy design architecture technical lead}

Very Frequently asked.

Q113. Explain throw, throws , try and catch in Java ?

Ans. throw is used to re throw an exception.throws is used to declare that the method throws the respective exceptions.try block is used to identify if the respective block has thrown any exception.catch is used to catch the exception that has been thrown by the respective try block.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java exception handling throw throws try catch Asked in 5 Companies basic frequent}

Q114. What is ConcurrentModificationException ?

Ans. This is the exception that is thrown when we try to modify the non concurrent collection class while iterating through it.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections concurrentmodificationexception exception concurrency Asked in 14 Companies intermediate}

Q115. Difference between jar , war and ear ?

Java EE

Ans. Jar is Java Archieve i.e compressed Class or Class / Java files.

War comprises of compressed Servlet class files,JSP FIles,supporting files, GIF and HTML files.

Ear comprise of compressed Java and web module files ( was files ).

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java j2ee jar web development war ear build management release management Asked in 12 Companies basic frequent}

Q116. What is the use of @GeneratedValue annotation in Hibernate?

Hibernate

Ans. This annotation is added to the auto increment column with the strategy to increment the column value. Usually this is added to the surrogate primary key column and specified with the Database Sequence.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve hibernate hibernate annotations @generatedvalue database sequence}

Q117. What is a BlockingQueue?

Data Structures

Ans. BlockingQueue is a Queue that supports operations that wait for the queue to become non-empty when retrieving and removing an element, and wait for space to become available in the queue when adding an element.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve blockingqueue collections java concurrent collections Asked in 10 Companies}

Q118. Which of the following collections stores its elements in insertion Order ?

a. HashMap
b. TreeMap
c. LinkedHashMap
d. LinkedMap

Ans. LinkedHashMap

Sample Code for LinkedHashMap

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve linkedhashmap collections java map}

Q119. In what order the elements of a HashSet are retrieved ?

a. Random Order
b. Insertion Order
c. Natural Sorting Order
d. Inverse Natural Sorting Order

Ans. Random Order

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve collections set hashset java}