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Q101. Explain Exception Hierarchy in Java SE ?

Ans. <a href="http://www.programcreek.com/2009/02/diagram-for-hierarchy-of-exception-classes/" rel="nofollow">http://www.programcreek.com/2009/02/diagram-for-hierarchy-of-exception-classes/</a>

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_{Like Discuss Correct / Improve exception hierarchy exceptions Asked in 3 Companies}

Frequently asked question in companies using Rest Web services.

Q102. Different between POST and PUT in Rest

Ans. PUT requests are only meant to place the object as it is on server. For example - You want a file to be uploaded and then placed in a particular folder or you want an Employee object to be persisted in the table.

POST requests are also meant to transfer information from client to server but that information once received at the server is evaluated , modified or refactored before persisting.

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_{Like Discuss Correct / Improve Put vs Post Rest Asked in 5 Companies frequent}

Q103. What are the benefits of Enums ?

Ans. Enums in Java are used to declare predefined objects and then reuse them. they offer many benefits

1. Enum instance are type safe and thread safe.

2. Enum instances are singleton and hence reused.

3. If we use Enums with Switch , It makes sure that the passed argument is either of its instance and hence provides a safeguard.

4. If we use Enum with Sorted Collections we can sort the elements with a predefined priorities ( as per constant declaration in enum )

5. We can use Enum as a Factory by defining its constructor.

6. We can store related constant data within enum. For example - If we know the values for the map upfront, we can alternatively use an enum.

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_{Like Discuss Correct / Improve Asked in 6 Companies}

Q104. How to Bulk upload the data into Oracle database?

Ans. We can use external table feature of Oracle.

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_{Like Discuss Correct / Improve Asked in 1 Companies Intermediate}

Frequently asked Design Pattern interview question.

Q105. What is a prototype design pattern ?

Ans. The prototype pattern is a creational design pattern. It is used when the type of objects to create is determined by a prototypical instance, which is cloned to produce new objects. Prototype is used when we need duplicate copies of objects.

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_{Like Discuss Correct / Improve design pattern prototype design pattern cloning Asked in 11 Companies intermediate}

Q106. Difference between Array and ArrayList ?

Ans. <a href="http://javahungry.blogspot.com/2015/03/difference-between-array-and-arraylist-in-java-example.html" rel="nofollow">http://javahungry.blogspot.com/2015/03/difference-between-array-and-arraylist-in-java-example.html</a>

Sample Code for ArrayList

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_{Like Discuss Correct / Improve array arraylist Asked in 11 Companies basic frequent}

Q107. What will be the crontab to run a job every last day of month ?

Ans. 59 23 28-31 * * [ "$(date +%d -d tomorrow)" = "01" ] && job_name

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_{Like Discuss Correct / Improve unix crontab Asked in 1 Companies}

Q108. Write a unix command to find top 10 files by size ?

Ans. du -a /var | sort -n -r | head -n 10

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Q109. What are fields that gets displayed when you execute "Top" command and briefly explain each field ?

Ans. PID - process identification number is an identification number that is automatically assigned to each process when it is created

USER - User Name

PR - PR is the process actual priority

NI is the nice value, which is a user-space concept.

VIRT -Virtual Image (kb). The total amount of virtual memory used by the task.

RES - Resident size (kb). The non-swapped physical memory a task has used.

SHR - Shared Mem size (kb). The amount of shared memory used by a task.

S - Process Status. The status of the task which can be one of:

D = uninterruptible sleep
R = running
S = sleeping
T = traced or stopped
Z = zombie

%CPU - % CPU usage

%MEM - % MEM Usage

TIME - Total CPU time the task has used since it started.

COMMAND - Command which was used to execute the process

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_{Like Discuss Correct / Improve top command unix command Asked in 1 Companies}

Q110. What is an exception and exception handling in Java ?

Ans. An Exception in java is the occurrence during computation that is anomalous and is not expected.

Exception handling is the mechanism which is used to handle such situations.

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_{Like Discuss Correct / Improve exception handling Asked in 18 Companies basic frequent}

Q111. Scale yourself on Java on the scale of 1 to 10

Ans. [Open Ended Answer]

The objective of the question is to check how efficient one is in the language so that appropriate level questions are asked. Don't tell too high number if you are being interviewed for a junior or mid level position as the interviewer may throw advance level questions.

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_{Like Discuss Correct / Improve Asked in 17 Companies}

Q112. Which environment variables do we need to set in order to run Java programs?

Ans. PATH, CLASSPATH and JAVA_HOME

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_{Like Discuss Correct / Improve environment variables path classpath java_home Asked in 3 Companies basic frequent}

Q113. Can an application have multiple main methods within different classes ? If yes, How will the app decide which one to be executed ?

Ans. Yes we can have a main method with string[] argument in every class of an application. When we execute an app we specify the starting point i.e the class that will get the control first and hence main method of that class gets executed.

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_{Like Discuss Correct / Improve main method Asked in 3 Companies}

Q114. Does importing a package imports all its sub packages too ?

Ans. No, but we can use wild card (*) to do so

For example -

import java.util.*

will import all packages with name starting with java.util

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_{Like Discuss Correct / Improve package import packages Asked in 1 Companies basic}

Q115. What is the default value of a declared object reference ?

Ans. Null

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_{Like Discuss Correct / Improve object reference null Asked in 1 Companies basic}

Q116. Is there a way to know size of an object in Java ?

Ans. No, Java doesn't have a sizeOf operator. In C / C++ , its required to determine how much memory allocation is required which is not the case with Java. Java handles memory allocation and deallocation intrinsically.

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_{Like Discuss Correct / Improve sizeOf size of object sizeOf operator Asked in 1 Companies rare}

Q117. What are the different ways to handle an exception ?

Ans. 1. Wrap the desired code in try block followed by a catch / finally to catch the exception

2. Declare the throws clause with exceptions that the code is expected to throw as an indication to the calling method to take care of it.

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_{Like Discuss Correct / Improve exception handling Asked in 4 Companies}

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Q118. How does Java handle integer overflows and underflows?

Ans. It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.

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_{Like Discuss Correct / Improve integer data types Asked in 1 Companies rare}

Q119. Is delete a keyword in Java ?

Ans. No, delete is not a keyword in Java. Destruction of objects is taken care by Java Garbage Collection mechanism.

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_{Like Discuss Correct / Improve delete keywords Asked in 1 Companies}

Q120. Is exit a keyword in Java ?

Ans. No exit is a method to exit execution of a program.

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_{Like Discuss Correct / Improve exit keywords exit a program Asked in 1 Companies}

Q121. Who invokes a thread's run method ?

Ans. After a thread is started using a call to start method, JVM invokes the thread’s run method when the thread is initially executed.

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Q122. How and Why Strings are interned in Java ?

Ans. String class has a public method intern() that returns a canonical representation for the string object. String class privately maintains a pool of strings, where String literals are automatically interned.

these are automatically interned so as to have efficient String comparison using == operator instead of equals which is usually slower.

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Q123. What are the different primitive data types in Java ?

Ans. boolean
byte
char
double
float
int
long
short
void

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_{Like Discuss Correct / Improve data types primitive data types Asked in 1 Companies Basic}

Q124. Write a Program to print duplicate words in a String

Ans. public class BuggyBread {
public static void main(String args[]) {
String str = "we are what we repeatedly Do excellence, then, is not an act but a haBit";
Set<String> words = new HashSet();
for(String word:str.split(" ")){
if(words.contains(word)){
System.out.println(word);
} else {
words.add(word);
}
}
}
}

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Q125. Write code to find second largest number in an array of integers.

Ans. int arr[]={1,3,5,6,4,8,9,2,10};
Arrays.sort();
System.out.println(arr[arr.length-1]);

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Frequently asked Spring interview question.

Q126. What are the components of Spring framework ?

Ans. Core: [Core, Bean, Context, Expression Language]

Web: [Web, Portlet, Servlet, etc]

Data Access [JMS, JDBC, etc]

AOP, Aspect

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_{Like Discuss Correct / Improve spring spring framework components Asked in 12 Companies}

Q127. Is synchronized a keyword , modifier, identifier? what is it ?

Ans. synchronized is a keyword and a modifier. The synchronized keyword is used to indicate that a method can be accessed exclusively by one thread at a time.

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_{Like Discuss Correct / Improve synchronization synchronized modifier identifier Asked in 2 Companies}

Q128. What is Amazon EC2 ?

Amazon Web Services (AWS)

Ans. Amazon Elastic Compute Cloud or EC2 provides scalable computing capacity in the AWS cloud. It can be used to create Virtual Environments , storage and configure. EC2 enables to upgrade or downgrade infrastructure according to the rules defined ( with fluctuation in latency, traffic etc )

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Q129. Difference between constructor and setter injection ?

Ans. 1. In Setter Injection, partial injection of dependencies can possible, means if we have 3 dependencies like int, string, long, then its not necessary to inject all values if we use setter injection. If you are not inject it will takes default values for those primitives1. In constructor injection, partial injection of dependencies cannot possible, because for calling constructor we must pass all the arguments right, if not so we may get error

2. Setter Injection will overrides the constructor injection value, provided if we write setter and constructor injection for the same property [i already told regarding this, hope you remember ] But, constructor injection cannot overrides the setter injected values

3. If we have more dependencies for example 15 to 20 are there in our bean class then, in this case setter injection is not recommended as we need to write almost 20 setters right, bean length will increase. In this case, Constructor injection is highly recommended, as we can inject all the dependencies with in 3 to 4 lines [i mean, by calling one constructor]

4. Setter injection makes bean class object as mutable [We can change ] .Constructor injection makes bean class object as immutable [We cannot change ]

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Q130. How to calculate lcm of two numbers ?

^{This question was recently asked at 'HCL Tech'.This question is still unanswered. Can you please provide an answer.}

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_{Like Discuss Correct / Improve coding code Asked in 1 Companies}

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