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Q751. What could be the real world example of Adapter Design Pattern ?

Design

Ans. Voltage converters / Power Adapters

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Q752. What is meant Java is "Write Once Run Anywhere" ?

Core Java

Ans. It means that Java is compiled to byte code that is platform independent and hence can be run anywhere or any machine.

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Q753. What is the difference between Enumeration and Iterator ?

Core Java

Ans. Enumeration can iterate only legacy collections like Vector , HashTable and Stack whereas Iterator can iterate both legacy and non legacy collections.

Enumeration is less safer than Iterator

Enumeration is fail safe whereas Iterator is fail fast

Iterator allows for removal of element while traversal whereas Enumeration doesn't have remove method.

Enumerations were introduced in Java 1 whereas Iterators were introduced with Java 2

Enumerations have methods like hasMoreElements and nextElement whereas Iterators have methods like hasNext, next and remove

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Q754. What are the four situations that are required for deadlock to happen ?

Operating System

Ans. mutual exclusion i.e the resource is not shareable and hence a process should have exclusive access to it at a particular time

Hold and Wait i.e the process doesn't release all existing resources held by it before requesting for another one.

No preemption i.e noone can forcefully release a resource held by another process and the process should voluntarily release the resource held by it.

Circular Wait - For ex, P1 is waiting on resource to be released by P2, P2 is waiting on resource to be released by P3 and P3 is waiting on the resource to be released by P1

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Q755. What is Livelock in relation to deadlock ?

Operating System

Ans. Livelock is when two threads or processes get deadlocked because they try to perform the same action to come out of a potential deadlock.

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Q756. What are the trade offs between public constructor and static final method ?

Core Java

Ans. Public constructor is simple and easy as it's the default way of object creation. So there are no additional coding overheads as compiler provides the default constructor if none is provided by coder.

With static final methods, it facilitates loose coupling by segregating the responsibility of object creation to a separate method. Validation can be done on the constructor arguments before calling it. Moreover if any adaption on the arguments is required that can achieved easily with factory method.On the flip side, there is coding overhead and additional method call.

Sample Code for constructor

Sample Code for factory

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Q757. What are the advantages and disadvantages of using lock classes from java.util.concurrent.locks vs. synchronized methods ?

Core Java

Ans. http://www.devinline.com/2015/10/Lock-Vs-synchronized-in-java.html

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Q758. What is the difference between CountingSemaphore and a CountDownLatch?

Operating System

^{This question is still unanswered. Can you please provide an answer.}

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Q759. Given a string and index for the opening bracket, find the index of matching closing bracket.

Core Java

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

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Q760. If we have to maintain a value "7" denoting "number of days in a week" as constant variable, Which of the following is the best constant name and Why ?

SEVEN
NUMBER_OF_DAYS_IN_WEEK
NUMBER_OF_DAYS_IN_WEEK_7

Core Java

Ans. NUMBER_OF_DAYS_IN_WEEK

Constant should be such that it uniquely identifies the value it holds and context of the value. SEVEN uniquely identifies the value but doesn't express the context.

Though NUMBER_OF_DAYS_IN_WEEK and NUMBER_OF_DAYS_IN_WEEK_7 makes sense in terms of unique value identification and context but 7 at the end of constant name appears useless as all weeks have 7 days and hence it's the only value it can hold. If it would have been "number of days in a month", it would have made sense to include number of days at the end like

NUMBER_OF_DAYS_IN_MONTH_30
NUMBER_OF_DAYS_IN_MONTH_31
NUMBER_OF_DAYS_IN_MONTH_27
NUMBER_OF_DAYS_IN_MONTH_28

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Q761. If we have to maintain a value "31" denoting "number of days in a month" as constant variable, Which of the following is the best constant name and Why ?

THIRTY_ONE
NUMBER_OF_DAYS_IN_MONTH
NUMBER_OF_DAYS_IN_MONTH_31

Core Java

Ans. NUMBER_OF_DAYS_IN_MONTH_31

Constant should be such that it uniquely identifies the value it holds and context of the value. THIRTY_ONE uniquely identifies the value but doesn't express the context. NUMBER_OF_DAYS_IN_MONTH expresses the context but doesn't specify the value clearly as different month can have different number of days.

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Q762. Would you consider creating a constant name for "null" ?

Core Java

Ans. Objective of constant variable is to provide a context to the value and provide a single point of change. In terms of context, i don't see much need for having constant name for null as null is already self explanatory. In terms of providing single point of change, it doesn't make much sense as it would necessitate that all such placeholders either hold null or a common value.

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Q763. Where does database stored procedures gets stored ?

Database

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

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Q764. What is a platform ? Is Java a Software or Hardware platforms ?

Core Java

Ans. Platform is the environment in which a program runs. Java provides a software platform for running JVM based applications and programs.

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Q765. What is the purpose of String Pool ? Don't you think it's a performance overhead to have unnecessary check for string in string pool ?

Core Java

Ans. String Pool makes Java more memory efficient by providing a reusable place for string literals. It might be a little performance inconvenience but results in good amount memory saving.

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Q766. What are the different layers of cloud computing ?

Infrastructure

Ans. Paas - Platform as a service
Iaas - Infrastructure as a service
Saas - Software as a service

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Q767. What is the use of @Bean annotation in Spring ?

Spring

Ans. There are 2 ways to specify dependencies in Spring, one by the way of specifying beans in config files and other is by specifying annotations like @Bean, @Component , @Service etc to let spring know of the dependencies.

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Q768. What are the benefits of assertThat over assert in Junits ?

Junit

Ans. assertThat is introduced with Junit4 and offers many advatanges over assert. Messages are more explanatory, offer better type safety and are more readable. Moreover hamcrest library is portable as it can used both with junit and TestNG.Moreover assertThat provides flexibility as the same method can be used for assert , assertEquals,assertTrue etc through the use of matcher methods.

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Q769. Can you name few matchers that can be used with hamcrest assertThat method ?

Junit

Ans. is
not
equals
anyOf
hasSize

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Q770. Which of following is / are valid static final declaration ?

public static final String MAX_NUM = "10";
public static final Object NULL = null;
public static final MathContext MATH_CONTEXT = new MathContext(2,RoundingMode.CEILING);

Core Java

Ans. All are valid declarations.

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Q771. Which of the following is valid greater than and equal to operator in Java ?

>=
=>

Core Java

Ans. >=

=> will result in error.

=> somewhat looks like lambda operator "->"

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Q772. If given a choice , which one would you prefer to send params to the Get service , path params or query param ?

Web Service

Ans. If the number of params is quite large , I would prefer to either split it with majority of it in query params or all in query params.

If the params are all mandatory , I would keep it as path params. If it's optional , I would keep it as query param so as to keep consistent base url.

If we don't require the param name , then they can be kept as path params as query params necessitates the usage of param name.

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Q773. Is it necessary to specify "employeeId" with @PathParam("employeeId") in this case,

@Path("/{employeeId}")
public String employeeInfo(@PathParam("employeeId") Long employeeId){
}

Rest

Ans. No, it's optional as the name of path param required is same as method param name in this case.

Even the declaration as following should work -

@Path("/{employeeId}")
public String employeeInfo(@PathParam Long employeeId){
}

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Q774. What is replication in Redis ? why do we need it ?

Redis

Ans. Asynchronous Replication of information from master to all slaves. Redis is an in memory storage and hence any crash may result in complete loss of information on a cluster.

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Q775. What is the difference between Oracle , Cassandra and Redis ?

Database

Ans. Oracle is a relational database. Cassandra is a noSQL Database whereas Redis is an inmemory cache.

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Q776. What are var args ?

or

What is the use of var args ?

Core Java

Ans. Var args is the feature of Java that allows a method to have variable number of arguments. Var args are used when we are not sure about the number of arguments a method may need. Internally java treats them as array.

Declarations of methods with var args

void method(int... x){};
void method(int x, int... y){};

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Q777. Why following method declarations are not valid ?

void method(int... x, int y){};
void method(int... x,int... y){};

Core Java

Ans. Because var args are not only allowed with the last argument in the method declaration.

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Q778. Can we catch errors in Java ?

Core Java

Ans. Yes we can

try {
// code
} catch (Error ex) {
// handling code
}

but we shouldn't ideally do that as errors are mostly JVM based and not application based and there is rarely we can do something about it. Very likely catching and not re throwing would lead to muting their response or trace.

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Q779. Do you see any problem with this code

public class BuggyBread {

   public static void main(String[] args) {
      method("Hello","World");
   }

   private static void method(String... args){
      for(String arg:args){
         System.out.println(arg);
      }
   }
}

Core Java

Ans. No, It will compile and execute perfectly fine. As we are using method with var args , we can call it with 0 to n arguments.

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Q780. Do you see any problem with this code

public class BuggyBread {

   public static void main(String[] args) {
      method();
   }

   private static void method(String... args){
      for(String arg:args){
         System.out.println(arg);
      }
   }
}

Core Java

Ans. This will compile fine as we can provide 0 arguments for a var arg but will print nothing upon execution.

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