Top X Restful Spider Web Service Interview Questions For Coffee Developers

REST is an architectural way of developing spider web services which receive got acquire immensely pop inwards the final distich of years together with consequently gained a lot of importance inwards inwardness Java together with Java EE interviews. If y'all are a Java spider web developer together with so y'all are most probable run into a distich of questions from spider web services every fourth dimension y'all buy the farm for a Java spider web developer interview. One of the most frequent ane is difference betwixt REST together with SOAP spider web services, which I receive got of late answered there, but at that topographic point are lot many other goodness questions I receive got collected from friends together with my readers, which I receive got non nonetheless published. In this article, I am sharing those questions, mainly based on REST-style spider web services for your practise together with preparation.

Some of them are slowly to respond together with y'all volition uncovering them either inwards my weblog or yesteryear doing Google but a distich of them is genuinely interesting together with challenging together with required existent corporation sense inwards Java spider web service domain to answer. I travel out it to y'all guys for right away together with volition in all likelihood update this postal service alongside answers inwards nigh future.

If y'all don't uncovering respond of whatever REST interview inquiry together with so I advise y'all to accept a aspect at these 2 resources, Java Programming Interview Exposed and RESTful Web Services, y'all volition most probable uncovering your respond there.

RESTful Web Services Interview Questions 

Here is my listing of RESTful spider web services questions for senior Java developers who receive got a distich of years of sense developing both SOAP together with REST based spider web services. This is genuinely the minute exercise of my serial of Java spider web services based question, inwards the before article, I receive got shared approximately SOAP spider web services based questions. If y'all receive got non looked already, y'all may desire to accept a look.



Question 1 : What is REST?
Answer : REST is an architectural way of developing spider web services which accept payoff of ubiquity of HTTP protocol together with leverages HTTP method to define actions. REST stands for REpresntational State Transfer.


Question 2 : What is RESTFul Web Service?
Answer : There are 2 pop way to develop spider web services, using SOAP (Simple Object Access Protocol) which is XML based way to let out spider web services together with minute REST based spider web services which uses HTTP protocol. Web services developed using REST way is likewise known equally RESTful Web Services.


Question iii : What is HTTP Basic Authentication together with how it works?


Question four : Can y'all tell me which API tin last used to develop RESTFul spider web service inwards Java?
Answer : There are many framework together with libraries out at that topographic point which helps to develop RESTful spider web services inwards Java including JAX-RS which is measure way to develop REST spider web services. Bailiwick of Jersey is ane of the pop implementation of JAX-RS which likewise offers to a greater extent than than specification recommends. Then y'all likewise receive got RESTEasy, RESTlet together with Apache CFX. If y'all similar Scala together with so y'all tin likewise exercise Play framework to develop RESTful spider web services.


Question five : How create y'all configure RESTFul spider web service?

Question vi : How y'all apply safety inwards RESTFul spider web services?

Question seven : Have y'all used securing RESTful APIs alongside HTTP Basic Authentication

Question 8 : How y'all keep session inwards RESTful services?


Question ix : Have y'all used Bailiwick of Jersey API to develop RESTful services inwards Java?
Answer : Bailiwick of Jersey is ane of the most pop framework together with API to develop REST based spider web services inwards Java. Since many organization uses Bailiwick of Jersey they banking company jibe if candidate has used it before or not. It's uncomplicated to answer, tell Yes if y'all receive got genuinely used together with No, if y'all receive got not. In instance of No, y'all should likewise get upwards which framework y'all receive got used for developing RESTful spider web services e.g. Apache CFX, Play or Restlet.


Question 10 : How y'all examine RESTful spider web services?

Question eleven : What is WADL inwards RESTFul?


Question 12 : What create y'all empathize yesteryear payload inwards RESTFul?
Answer : Payload way information which passed within asking torso likewise payload is non asking parameters. So alone y'all tin create payload inwards POST  and non inwards GET together with DELTE method


Question thirteen : Can y'all create payload inwards GET method?
Answer : No, payload tin alone last passed using POST method.


Question fourteen : Can y'all create payload inwards HTTP DELETE?
Answer : This is in ane lawsuit again similar to previous REST interview question, respond is No. You tin alone overstep payload using HTTP POST method.


Question fifteen : How much maximum pay charge y'all could create inwards POST method?
Answer : If y'all cry back difference betwixt GET together with POST request together with so y'all know that dissimilar GET which passes information on URL together with thence express yesteryear maximum URL length, POST has no such limit. So, theoretically y'all tin overstep unlimited information equally payload to POST method but y'all necessitate to accept practical things into concern human relationship e.g. sending POST alongside large payload volition eat to a greater extent than bandwidth, accept to a greater extent than fourth dimension together with acquaint surgical operation challenge to your server.


Question sixteen : What is deviation betwixt SOAP together with RESTFul spider web services?
Answer : There are many deviation betwixt these 2 way of spider web services e.g. SOAP accept to a greater extent than bandwidth because of heavy weight XML based protocol but REST takes less bandwidth because of pop exercise of JSON equally message protocol together with leveraging HTTP method to define action. This likewise way that REST is faster than SOAP based spider web services. You tin derive many differences betwixt SOAP together with RESTful alongside the fact that its HTTP based e.g. REST URLs tin last cached or bookmarked. Here are few to a greater extent than differences betwixt them :

Question 17 : If y'all receive got to develop spider web services which ane y'all volition select SOAP OR RESTful together with why?
Answer : You tin respond this inquiry based upon your sense but the fundamental hither is if y'all know deviation betwixt them than y'all tin respond this inquiry inwards to a greater extent than detail. For example, its slowly to develop RESTful spider web services than SOAP based spider web services but later on comes alongside approximately in-built safety features.


Question xviii :  What framework y'all had used to develop RESTFul services?
Answer : This is genuinely sense based question. If y'all receive got used Bailiwick of Jersey to develop RESTFul spider web services together with so respond equally Bailiwick of Jersey but await approximately follow-up inquiry on Jersey. Similarly if y'all receive got used Apache CFX or Restlet together with so respond them accordingly.


That's all inwards this listing of approximately goodness RESTful spider web service interview questions for Java developers. Though this listing is meant for Java developer, y'all tin exercise this questions to banking company jibe whatever candidate's noesis on REST way spider web services independent of programming linguistic communication because REST doesn't tell that y'all necessitate to implement spider web service inwards Java only. Since it accept payoff of ubiquitous HTTP protocol y'all tin create backed alongside whatever spider web applied scientific discipline stack e.g. Java, .NET or whatever other.

Further Learning
REST Java Web Services
REST API Automation testing from scratch-(REST Assured java)
RESTFul Services inwards Java using Bailiwick of Jersey By Bryan Hansen

P.S. - If y'all are looking for online preparation to larn how to develop RESTful Web Services inwards Java using Spring framework, I advise y'all joining Eugen Paraschiv's REST alongside Spring course. The class has diverse options depending upon your sense degree together with how much y'all desire to larn e.g. beginner's class, intermediate class, together with master copy class. You tin bring together the ane which suits y'all better, though I advise joining the master copy class if y'all are serious nearly becoming an skillful Java REST developer.

Why Y'all Shouldn't Role == Amongst Float Together With Double Inward Java?

In this article, you lot are going to acquire why you lot shouldn't purpose == amongst float too double inwards Java? Especially for checking loop outcome condition. Java programmers oft brand the mistake of using floating request number inwards a loop too checking status amongst the == operator, inwards the worst instance this could create an infinite loop, causing your Java application to hung.


For example, next code volition non function equally you lot facial expression :

for(double balance = 10; balance!=0; balance-=0.1) {    System.out.println(balance); }

You would mean value that this code volition impress residual until residual reduced to zero. Since nosotros are doing balance = residual - 0.1, you lot  would facial expression it to impress something similar 10, 9.9, 9.8 too thence on until it reaches zero. But for your surprise, this volition elbow grease an infinite loop inwards Java, it volition never end, Why? because 0.1 is an infinite binary decimal, the residual volition never last just 0.

This is the argue many programmers, including Joshua Bloch, has propose to avoid using double too float for monetary calculation inwards his mass Java Puzzlers.

Now, this brings a to a greater extent than pertinent question, how do you lot compare floating request numbers inwards Java? if == is non going to function too thence how tin I write a similar loop, because that's a real full general instance too it would last unfortunate if you lot can't evidence for decimal points? Let's respect out the correct agency to compare floating request values inwards Java inwards adjacent section.

How to compare float too double values inwards Java?

As nosotros receive got seen inwards the outset paragraph that purpose of == operator tin elbow grease an endless loop inwards Java, but is at that spot a agency to forestall that loop from running infinitely? Yes, instead of using equality operator (==), you lot tin purpose relational operator e.g. less than (<) or greater than (>) to compare float too double values.



By changing the higher upwards code equally following, you lot tin forestall the loop from infinitely  :

for(double balance = 10; balance > 0; balance-=0.1) {    System.out.println(balance); }

If you lot mean value a trivial flake too thence you lot volition realize that greater than volition definitely goal this loop, but don't facial expression it to impress numbers similar 9.9, 9.8, 9.7 because floating request numbers are a only approximation, they are non exact. Some numbers e.g. 1/3 cannot last represented just using float too double inwards Java.

After running next programme on your estimator you lot may goal upwards amongst something similar this

/**  * Don't purpose == operator amongst float too double values inwards Java  *  * @author Javin Paul  */ public class FloatInForLoop {     public static void main(String args[]) {         for (double residual = 10; residual > 0; residual -= 0.1) {             System.out.println(balance);         }     } } Output: 10.0 9.9 9.8 9.700000000000001 9.600000000000001 9.500000000000002 9.400000000000002 9.300000000000002 ... .... 0.9000000000000187 0.8000000000000187 0.7000000000000187 0.6000000000000187 0.5000000000000188 0.4000000000000188 0.3000000000000188 0.2000000000000188 0.1000000000000188 1.8790524691780774E-14

You tin come across that number is nowhere to a greater extent than or less our expectation, too that's why float too double are non recommended for fiscal calculation or where the exact number is expected.

Some tips spell using float too double inwards Java

Do all calculation inwards float/double but for comparison, e'er compare approximation instead of precise values e.g. instead of checking for 10.00 depository fiscal establishment agree for > 9.95 equally shown below

if (amount == 100.00) // Not Ok if (amount > 99.995)  // Ok

One reason, why many programmers make mistake of comparing floating points number amongst == operator is that, for some fraction it does function properly e.g. if nosotros change 0.1 to 0.5 the loop inwards query volition function properly equally shown below :

for (double balance = 10; balance > 0; balance -= .5) {    System.out.println(balance); }  Output : 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5

Alternatively, you lot tin purpose BigDecimal for exact calculation.  You tin too elbow grease rewriting the same code using BigDecimal shape instead of double primitive.

That's all virtually why you lot shouldn't purpose == operator amongst float too double inwards Java. If you lot receive got to depository fiscal establishment agree status involving float too double values than instead of using == e'er purpose relational operator e.g. < or > for comparing floating request numbers inwards Java. I repeat, don't purpose double too float for monetary calculation unless you lot are practiced of floating request numbers, knows virtually precision too receive got real goodness agreement of floating request arithmetics inwards Java.

Further Learning
Complete Java Masterclass
Java Fundamentals: The Java Language
Java In-Depth: Become a Complete Java Engineer!

Factorial Inward Coffee Using Recursion Together With Loop

Problem : Write a plan to calculate factorial of a given reveal inwards Java, using both recursion too iteration.

Solution : If yous come upward from Maths background too so yous know that factorial of a reveal is number*(factorial of reveal -1). You volition run this formula to calculate factorial inwards this  Java tutorial. Since factorial is a naturally recursive operation, it brand feel to run recursion to solve this work precisely its non ever the best way. Iteration provides a to a greater extent than robust way, precisely don't worry yous volition larn how to calculate factorial amongst too without recursion inwards Java. By the way, factorial of numbers grows really chop-chop too fifty-fifty the largest integral information type inwards Java, long is non able to concur factorial of anything or to a higher house 50. In such cases yous tin run BigInteger, which has theoretically no boundary too tin live used to stand upward for really large integral numbers.

Solution 1 : Factorial using recursion

In companionship to practice a recursive solution yous necessitate a base of operations example where plan terminates too inwards this work base of operations example is factorial of 1, which is 1. So if given reveal is greater than 1, nosotros continue applying factorial formula too recursive telephone telephone this method amongst n - 1 equally shown below :

 public static long factorial(int number){                 //base example - factorial of 0 or 1 is 1         if(number <=1){             return 1;         }                 return number*factorial(number - 1);     }

Once input move yesteryear 1 the method stopped recursive telephone telephone too render 1. From at that spot onward stack started to curl downwards too lastly factorial of reveal is calculated.

Solution 2 : Factorial without Recursion

As I said instead of using recursion too calling factorial method ane time to a greater extent than yous tin likewise run for loop to calculate factorial because !n = n*(n-1)*(n-2).....*1 , which tin easily live implemented using loop equally shown below :

public static long factorial(long input){         long factorial = 1L;         for(long i= input; i > 0; i--){             factorial = factorial * i;         }                  return factorial;     }

You tin meet that nosotros outset amongst the reveal too multiply it amongst the factorial which is initialized amongst 1 too so nosotros cut the reveal yesteryear 1 until reveal becomes 1, which is nix but n*(n-1)*(n-2).....*1.

Java Program to calculate Factorial amongst too without Recursion

Here is our consummate solution of this problem. You tin meet that I receive got created two factorial() method, ane receive got int too render long e.g. long factorial(int number), piece other receive got a long too render a long factorial i.e. long factorial(long number). Since their parameter type is unlike they are 2 unlike method likewise known equally overloaded methods. First method uses recursion to calculate factorial piece minute method uses iteration to calculate factorial.

import java.math.BigInteger; import java.util.Calendar; import java.util.Date; import java.util.GregorianCalendar;  /**  * Java Program to calculate factorial using iteration too recursion  *   * @author WINDOWS 8  *  */ public class FactorialTest {      public static void main(String args[]) {                 System.out.println("factorial of 1 using recursion : " + factorial(1));         System.out.println("factorial of 1 using iteration : " + factorial(1L));                  System.out.println("factorial of five using recursion : " + factorial(5));         System.out.println("factorial of five using loop : "   + factorial(5L));                         System.out.println("factorial of seven using recursive algorithm : " + factorial(7));         System.out.println("factorial of seven using iterative algorithm : " + factorial(7L));               }         /**      * Java method to calculate factorial of given integer using recursion.      * @param reveal      * @return factorial of reveal      */     public static long factorial(int number){                  //base example - factorial of 0 or 1 is 1         if(number <=1){             return 1;         }                  return number*factorial(number - 1);     }          /**      * Java method to calculate factorial of given reveal using iteration      * @param input      * @return factorial of input      */     public static long factorial(long input){         long factorial = 1L;         for(long i= input; i > 0; i--){             factorial = factorial * i;         }                  return factorial;     }      }  Output : factorial of 1 using recursion : 1 factorial of 1 using iteration : 1 factorial of 5 using recursion : 120 factorial of 5 using loop : 120 factorial of 7 using recursive algorithm : 5040 factorial of 7 using iterative algorithm : 5040

That's all most how to calculate factorial of a reveal inwards Java using both recursion too iteration. This work is oft used to instruct programming, especially recursion inwards schoolhouse too colleges too its proficient ane equally well. Just scream back that fifty-fifty though recursive solution are pocket-size too clear they are prone to throw StackOverFlowException, thence non suitable for production code. Iteration or run of for loop results inwards to a greater extent than robust solution.

Further Learning
The Coding Interview Bootcamp: Algorithms + Data Structures
Data Structures too Algorithms: Deep Dive Using Java
solution)

How to respect if given String is palindrome inwards Java? (solution)

How to opposite an int variable inwards Java? (solution)

How practice yous swap 2 integers without using temporary variable? (solution)

Write a plan to depository fiscal establishment jibe if a reveal is ability of 2 or not? (solution)

How to opposite String inwards Java without using StringBuffer? (solution)

How practice yous opposite give-and-take of a judgement inwards Java? (solution)

How to respect a missing reveal inwards a sorted array? (solution)

How To Course Of Teaching Hashset Inwards Java? Example

Somebody asked me recently, how produce you lot variety an HashSet? For lists, nosotros operate the Collections.sort(List) method, exactly at that spot is cypher for Set. If I accept an HashSet together with thence how would I become nearly sorting it? The respond is you lot cannot variety an HashSet, why? because HashSet is an unordered collection. When you lot insert an chemical factor inwards HashSet than you lot lose the club guarantee. You cannot produce reordering or sorting inwards Set because it does non accept random access methods (ie, .get() an chemical factor at a given index), which is basically required for variety algorithms. Though you lot tin variety the HashSet past times kickoff converting HashSet to List together with and thence sorting it. Also, about of Set implementation may acquire out along the club intact e.g. LinkedHashSet maintains insertion order, which agency you lot tin variety LinkedHashSet but non HashSet. Alternatively, you lot tin likewise operate TreeSet to acquire out along elements inwards the sorted club from the start.

In short, you lot cannot variety HashSet straight exactly you lot tin produce thence past times converting it into List together with and thence sorting a List together with accessing elements from it inwards sorted club for farther processing. If you lot are novel inwards Java together with wants to larn Java Collection framework inwards deep, together with thence you lot tin likewise check Java Generics together with Collection book, 1 of the best on generics together with collection.

How to variety HashSet inwards Java

Here is a unproblematic Java programme which attempts to variety a HashSet kickoff past times converting it into List together with likewise past times using TreeSet, which is your sorted set. I accept kickoff created an HashSet of String together with stored pair of names inwards arbitrary order. Later I accept printed the HashSet to exhibit that elements are non stored inwards whatsoever order. After that nosotros accept converted our HashSet to ArrayList together with sorted it using Collections.sort() method. You tin come across elements inwards sorted club inwards our instant impress statement. But this is non the entirely way together with you lot tin likewise operate TreeSet to variety HashSet elements every bit shown inwards instant instance .

answer)

How HashSet internally industrial plant inwards Java? (answer)

Difference betwixt HashSet together with TreeSet inwards Java? (answer)

What is departure betwixt ArrayList together with HashSet inwards Java? (answer)

How produce you lot loop through HashSet inwards Java? (code)

How to variety array using QuickSort Algorithm inwards Java? (solution)

How to variety an ArrayList inwards descending club inwards Java? (example)

How to variety objects inwards Java? (answer)

Difference betwixt HashSet together with HashMap inwards Java? (answer)

Difference betwixt LinkedHashSet, TreeSet together with HashSet inwards Java? (answer)

How to variety HashMap past times values inwards Java? (code)

Bubble variety algorithm inwards Java (implementation)

How to variety List inwards increasing club inwards Java? (answer)

4 ways to variety an Array inwards Java? (program)

2 ways to variety an HashMap inwards Java? (solution)

How insertion variety algorithm industrial plant inwards Java? (answer)

How To Role Biginteger Cast Inwards Java? Large Factorial Example

When yous calculate factorial of a relatively higher release most of the information type inwards Java goes out of their limit. For example, yous cannot purpose int or long variable to shop factorial of a release greater than 50. In those scenarios where int in addition to long are non large plenty to stand upward for an integral value, yous tin purpose java.math.BigInteger class. BigInteger variable tin stand upward for whatever integral number, at that topographic point is no theoretical limit, exactly it allocates alone plenty retentivity required to concur all the bits of information it is asked to hold. There is non many fourth dimension yous demand this degree exactly its proficient to know virtually it in addition to that's why I am giving 1 scenario which is perfectly suitable for using BigInteger class. In this article, yous volition larn how to calculate factorial of large release using BigInteger object. We volition purpose same formula, nosotros convey used to calculate normal factorials equally discussed inwards my previous post virtually factorials.

How to purpose BigInteger degree inwards Java

Here is our sample Java programme to calculate large factorials. You volition purpose BigInteger degree to concur the effect of calculation. Remember this degree is non within java.lang package, so yous demand to explicitly import it, equally nosotros convey done inwards this example.  Another matter to piece of job out on inwards hear is that, this degree is Immutable in addition to whatever alter on BigInteger object volition effect inwards about other object. So, if yous forget to shop the effect back, yous volition lose it. Original object volition e'er rest inwards same the world fifty-fifty later addition, subtraction or multiplication.

import java.math.BigInteger;  /**  * Java Program to calculate factorial of large numbers using BigInteger class.  *  * @author WINDOWS 8  */ public class BigIntegerDemo {      public static void main(String args[]) {         BigInteger effect = factorial(BigInteger.valueOf(5));         System.out.println("factorial of v : " + result);          effect = factorial(BigInteger.valueOf(10));         System.out.println("factorial of 10 : " + result);                  effect = factorial(BigInteger.valueOf(50));         System.out.println("factorial of 50 : " + result);     }      /**      * Java method to calculate factorial of large number.      *      * @param release BigInteger      * @return factorial of release equally BigInteger      */     public static BigInteger factorial(BigInteger number) {          // factorial of 0 in addition to 1 is e'er 1 - base of operations case         if (number == BigInteger.ZERO || release == BigInteger.ONE) {             return BigInteger.ONE;         }                   // !n = n*!n-1 - recursive telephone phone               return number.multiply(factorial(number.subtract(BigInteger.ONE)));      }  }  Output : factorial of 5 : 120 factorial of 10 : 3628800 factorial of 50 : 30414093201713378043612608166064768844377641568960512000000000000

There is no maximum in addition to minimum bound of BigInteger class, inwards theory at that topographic point is no bound for BigInteger. You should purpose BigInteger whenever yous demand to stand upward for a large integer number, i.e. something which is non floating signal exactly cannot hold upward represented using long information type.

Things to Remember :
1. BigInteger degree is inwards java.math package, in addition to so yous demand to specifically import it, it volition non hold upward imported automatically similar java.lang package.

2. Similar to String, BigInteger class is likewise immutable, in addition to so whatever change e.g. addition, multiplication volition orbit a novel instance of BigInteger, leaving master copy object intact.

3. Theoretically BigInteger has no bound of numbers.

4. BigInteger class helps to bargain amongst really large numbers inwards Java.

promise this helps.

Further Learning
Complete Java Masterclass
Java Fundamentals: The Java Language
Java In-Depth: Become a Complete Java Engineer!

60+ Coffee Interview Questions For Quick Revision

Java Interviews are real dissimilar than traditional software developer interviews. You tin clear a Java interview without fifty-fifty writing a unmarried describe of piece of job of code, Yes, this is true, you lot tin perish a Java developer without mortal scream for you lot to write a role inward Java interview. Though it's non the instance everywhere in addition to many companies are increasing including a coding assay inward their Java developer interview process, simply in that place are many companies in addition to start-ups where you lot tin teach a Java task without writing a unmarried describe of piece of job of code. All you lot demand to orbit is memorize those criterion Java questions, which has been asked from ages in addition to generally assay the theoretical noesis of the candidate. This is swell for candidates which lack hands-on coding experience, simply sometimes this trend of the interview tin terms you lot expert developers who are non expert at interviews. Someone, who knows how to construction a complex program, knows how to model their bird in addition to objects, tin write good, robust code simply neglect to respond questions like, Why String is Immutable? or How HashMap plant inward Java?


Since I own got gone through a lot of such interviews in addition to fifty-fifty conducted yoke of them, I idea to compile a listing of around of the most oft asked Java interview questions, roofing cardinal topics similar pattern patterns, pattern principles, OOP, JVM internals, Garbage collection, multithreading, generics in addition to collections, XML parsing in addition to others. This listing is collection fo such questions. I own got non answered them correct hither because I own got already answered them inward their private post service inward this blog, you lot tin see the respond link to run across the answer. 

Java Interview Questions for Freshers in addition to Experienced

1) What is Composite pattern pattern?

2) Explain Liskov exchange principle?

3) Write a Java programme to convert bytes to long?

4) What is faux sharing inward multithreading Java?

5) Can nosotros brand an array volatile inward Java? What is the number of making it volatile? (answer)

6) What is wages in addition to disadvantage of busy spin waiting strategy? (answer)

7) H5N1 deviation betwixt DOM in addition to SAX parser inward Java? (answer)

8) Write wait-notify code for producer-consumer problem? (solution)

9) Write code for thread-safe Singleton inward Java? (answer)

10) What are four ways to iterate over Map inward Java? Which ane is best in addition to why? (solution)

11) Write code to take elements from ArrayList spell iterating? (example)

12) is Swing thread-safe? (answer)

13) What is thread local variable inward Java? (answer)

14) How orbit you lot convert a String to engagement inward Java? (example)

15) Can nosotros usage String inward the switch case? (Yes)

16) What is constructor chaining inward Java? (answer)

17) Explain Java Heap infinite in addition to Garbage collection? (answer)

18) Difference between major in addition to nipper GC? (answer)

19) Difference between -Xmx in addition to -Xms JVM option? (answer)

20) How to banking concern fit if a String contains exclusively numeric digits? (regular expression)

21) Difference between poll() in addition to remove() method of Queue inward Java?

22) Difference between Comparator in addition to Comparable inward Java? (answer)

23) Why you lot demand to override hashCode, when you lot override equals inward Java? (answer)

24) How HashSet plant internally inward Java? (answer)

25) How orbit you lot impress Array inward Java? (answer)
26) Explain what 'path to root' way inward the context of garbage collection. What are roots?

27) Write code for a uncomplicated implementation of HashMap/Hashtable

28) Write a brusk programme to illustrate the concept of deadlock

29) Explain why recursive implementation of QuickSort volition require O(log n) of additional space

30) Explain the pattern pattern used inward Java in addition to .NET io stream/reader APIs.

31) Create an Iterator filtering framework: an IObjectTest interface amongst a unmarried boolean test(Object method in addition to an Iterator sub-class which is initialized amongst around other Iterator in addition to an IObjectTest instance. Your iterator volition hence allow iteration over the original, simply skipping whatever objects which don't transcend the test. Create a uncomplicated unit of measurement assay for this framework.

32) Difference betwixt Abstract bird in addition to Interface - given a province of affairs what would you lot conduct betwixt abstract bird in addition to interface? (answer)

33) Difference betwixt inheritance in addition to composition? (answer)

34) Difference betwixt ArrayList in addition to linked list? (answer)

35) Difference betwixt slumber in addition to wait? (answer)

36) Explain almost HashMap (methods inward HashMap in addition to  the projection inward which nosotros own got used the HashMap to a greater extent than almost equals() in addition to hashCode()  (answer)

37) Explain the methods inward Object class? (answer)

38) What is coupling? How orbit you lot cut down coupling in addition to why?

39) Struts config file - tin in that place last multiple configs? (answer)

40) Design patterns - factory, abstract factory, singleton implemented? (answer)

41) What does static, in conclusion mean, purposes; (answer)

42) How many accessibility modifiers exist? Please depict them. (answer)

43) Why orbit you lot demand a top dog method? (answer)

44) How many constructors tin you lot have?

45) Define overwriting in addition to overloading? (answer)

46) Give coffee API implementations for overwriting in addition to overloading

47) Describe the String bird – unique properties (answer)

48) StringBuilder vs StringBuffer? differences? (answer)

49) Collections: delight describe, give around examples in addition to compare them to each other

50) ArrayList vs Vector? Differences, when to usage which information structure? (answer)

51) HashMap vs Hashtable (answer)

52) What’s a tree inward Java? How dissimilar is from the tree inward information structure?

53) What’s a map? 

54) Multithreading: depict the thread management inward Java?

55) What’s a semaphore? (answer)

56) How many states are in that place for threads?

57) Describe the usage for synchronized discussion (2)? (examples)

58) Serialization inward coffee – a description in addition to usage? (example)

59) Garbage collection inward coffee – description in addition to usage

61) Can you lot guarantee the garbage collection process? No

62) Singleton, delight depict top dog features in addition to coding (answer)

63) Factory. delight depict top dog features in addition to coding (answer)

64) Have you lot used others? delight depict them?

What is the travel of this listing of  Java Interview questions?
The sole travel is to deport mock Java interviews past times yourself. You tin usage this listing to orbit in conclusion infinitesimal revision. Since answers are non provided, you lot tin endeavour answering them in addition to if you lot tin hence you lot are laid to accept on whatever telephonic circular of Java interview or face-to-face circular which doesn't involve coding.

6 Ways To Convert Char To String Inward Coffee - Examples

If yous receive got a char value e.g. 'a' as well as yous desire to convert it into equivalent String e.g. "a" as well as hence yous tin forcefulness out utilisation whatever of the next 6 methods to convert a primitive char value into String inwards Java :

1) String concatenation
2) String.valueOf()
3) Character.toString()
4) Character wrapper degree + toString
5) String constructor alongside char array
6) String.valueOf(char [])

In this article, nosotros volition come across examples of each approach as well as larn a petty flake to a greater extent than nearly it. Actually, at that spot is lot of overlap betwixt each method equally to a greater extent than or less of them internally calls String.valueOf(), which eventually calls to a String constructor which accepts char array as well as creates a String object containing primitive char value alongside length 1. Once yous know, how they locomote internally, it tardily to create upward one's hear which i is to a greater extent than efficient for purpose.

Char to String using concatenation

This is the easiest agency to convert a char to String object inwards Java. All yous necessitate to produce is concatenate given grapheme alongside empty String, equally shown inwards the next example:

char apple tree = 'a'; String aStr = "" + apple; System.out.println("char to String using concatenation : " + aStr);   // a

Remark: This is the simplest method to convert a char value to String but it's less efficient as well as takes to a greater extent than retention than required. Compile interpret String concatenation into the next code:

new StringBuilder().append(x).append("").toString();

This is less efficient because the StringBuilder is backed past times a char[] of size 16, which is a waste materials of retention if yous simply converting i character. This array is as well as hence defensively copied past times the resulting String

Character to String using String.valueOf()

This is the criterion agency to convert a char primitive type into String object. If yous remember, nosotros receive got already used the valueOf() method to convert String to int as well as String to double inwards Java. Here is the instance of using this method to convert char to String:

char man child = 'b'; String bStr = String.valueOf(boy); System.out.println("char to String using String.valueOf() : " + bStr); // "b"

Remark: String.valueOf(char) is the most efficient method for converting char to String inwards Java, because it simply uses a grapheme array of size i to roll given grapheme as well as transcend it to String constructor, equally shown below (from JDK) :

Char to String conversion alongside Character.toString()

This is the 3rd instance to convert a char primitive value to a String object inwards Java. In this example, nosotros receive got used Character.toString() method.

char truthful cat = 'c'; String cStr = Character.toString(cat); System.out.println("char to String using Character.toString() : " + cStr);

Remark: This method returns a String object representing the given char. It returns a String of length i consisting alone of the specified char. Internally it likewise calls String.valueOf(char c) method.

BTW, hither is squeamish summary of all the six ways to convert a char value to String object inwards Java:

Char to String using Character wrapper class

This is the quaternary instance of converting a char value to String object inwards Java. This time, nosotros volition utilisation java.lang.Character class, which is a wrapper for char primitive type.

char Canis familiaris = 'd'; String dStr = new Character(dog).toString(); System.out.println("char to String using novel Character() + toString : " + dStr);

Remark: This method returns the String equivalent of Character object's value of length 1. Internally this method wraps the encapsulated char value into a char array as well as passed to String.valueOf(char[]) method.

String constructor alongside char array

Here is i to a greater extent than agency to convert a char value to String object inwards Java. In this example, nosotros receive got wrapped the unmarried grapheme into a grapheme array as well as passed it to a String constructor which accepts a char array equally shown below:

String fStr = new String(new char[]{'f'}); System.out.println("char to String using novel String(char array) : " + fStr);

Remark: This is the method which is internally called past times String.valueOf() method for char to String conversion. This constructor allocates a novel String object to stand upward for a sequence of characters passed via char array argument. The contents of the grapheme array are defensively copied hence that subsequent alteration of the grapheme array doesn't impact the newly created String.

char to String using String.valueOf(char[])

This the 6th as well as terminal agency to perform char to String conversion inwards our article, hither is the sample code:

String gStr = String.valueOf(new char[]{'g'}); System.out.println("char to String using String.valueOf(char array) : " + gStr);

Remark: String.valueOf() is overloaded to convey both char as well as char[]. Since the valueOf() method which convey a char, internally roll that char into a grapheme array it brand feel to utilisation this overloaded method to straight transcend a char array, which inwards plow passed to String constructor which accepts a grapheme array.


That's all nearly how to convert a char value to String inwards Java. You tin forcefulness out select whatever of the higher upward methods, which suits your essay out but remember, String concatenation is non efficient as well as tin forcefulness out waste materials a lot of memories if used inwards the loop. String.valueOf() is to a greater extent than readable as well as efficient, hence should hold upward your default choice. All of the higher upward methods internally uses new String(char[]) though.

Further Learning
Data Structures as well as Algorithms: Deep Dive Using Java
Java Fundamentals: The Java Language
Complete Java Masterclass

Thread-Safe Singleton Inwards Coffee Using Double Checked Locking Idiom

Singleton Pattern is 1 of the famous blueprint patterns from the Gang of Four. Even though demo it is considered equally an anti-pattern, it has served us good inward the past. In Singleton pattern, a flat has simply 1 instance throughout its lifetime in addition to that instance is shared betwixt multiple clients. Singleton flat has ii responsibility, offset to ensure that alone instance of the flat gets created in addition to second, supply a method getInstance() so that everyone tin acquire access to that unmarried instance i.e. global access. One of the issue, faced past times Singelton blueprint pattern inward the multi-threading plan is to ensure that simply 1 instance of the flat gets created, fifty-fifty if multiple clients called getInstance() method same time. Many programmers solved this occupation past times making whole getInstance() method synchronized, which results inward pitiful functioning because every fourth dimension a thread enters a synchronization method, it acquires the lock in addition to piece it's been within the method, no other thread are allowed to enter, fifty-fifty if they are non creating instance in addition to simply accessing already created instance.

How exercise you lot solve this problem? Well, you lot tin role Double checked locking idiom, which you lot acquire inward this article. Btw, if you lot are curious virtually why Singleton is considered anti-pattern, I highly recommend the majority Games Programming Patterns past times Robert Nystrom, though examples are inward C++, it's 1 of the most readable books on blueprint pattern, you lot won't experience bored or cheated.

Threadsafe Singleton using Double Checked Locking Idiom

Double checked locking idiom solves this occupation past times allowing you lot to consume your cake in addition to convey it equally well, it ensures synchronization is used alone when instance of Singleton is created, when getInstance() method is called offset fourth dimension in addition to all other time, same instance is returned without whatsoever synchronization overhead. As the mention suggests, it's double-checked, which agency it checked ii times whether _instnace (the singleton instance) is initialized or not, 1 without synchronization in addition to other alongside synchronization. This double depository fiscal establishment tally ensures that locking is alone used when an instance is naught i.e. when offset fourth dimension individual calls getInstance(), all subsequent telephone outcry upward volition run across _instnace non naught thus they volition non acquire inward into synchronization block.


Here is the code of thread-safe singleton pattern using double-checked locking idiom:

/**  * Thread Safe Singleton inward Java using Double checked locking.  * @author WINDOWS 8  *  */ public class Singleton {      private static volatile Singleton _instance;      /**      * Double checked locking code on Singleton      * @return Singelton instance      */     public static Singleton getInstance() {         if (_instance == null) {             synchronized (Singleton.class) {                 if (_instance == null) {                     _instance = new Singleton();                 }             }         }         return _instance;     }  }

How Double Checked Locking Idiom Works

To illustrate the point, how this idiom prevents from ii instances existence created when ii thread simultaneously calls the getInstance() method, let's run across the theory. Suppose, thread T1 calls getInstance() really the offset fourth dimension in addition to sees that _instance is null then it volition acquire within synchronization block in addition to that betoken of fourth dimension it paused. Now, thread T2 calls getInstance() in addition to it volition too run across _instance variable null, but it cannot acquire within synchronization block because the lock is held past times Thread T1, which is within the synchronization block. Now, thread T1 wake upward in addition to creates a novel instance of singleton in addition to come upward out of synchronized block.  After this when thread T2 goes within synchronized block, it over again checks whether _instance is null in addition to this fourth dimension depository fiscal establishment tally fails because _instnace is no to a greater extent than null. So thread T2 come upward out of the synchronized block without creating simply about other instance.  Further calls to this method render from offset depository fiscal establishment tally only.

By the way, double checked locking idiom was broken earlier Java 5. It was possible for a thread to run across one-half initialized instance which volition neglect the offset naught check, resulting inward returning a half-initialized Singleton. That's why it's absolutely critical to brand _instnace a volatile variable. The Java retentivity model updates in addition to happens-before makes double checked locking plant again.

That's all virtually how to create thread-safe Singleton inward Java, but this is non the alone way to create the thread-safe singleton. You tin role Enum equally Singleton so Java itself volition guarantee that alone 1 instance  volition last created fifty-fifty inward the instance of multiple threads trying to access it the same time. Alternatively, you lot tin too eagerly initialized the Singleton, inward that case, it would last initialized on static initializer block at the fourth dimension of flat loading inward a thread-safe manner.  If you lot create upward one's hear to role double-checked locking idiom to brand Singleton creation thread-safe, don't forget the volatile modifier.

Recommended courses
Design Pattern Library
From 0 to 1: Design Patterns - 24 That Matter - In Java
Java Design Patterns - The Complete Masterclass

Further Reading
If you lot desire to acquire to a greater extent than virtually condom publication techniques inward concurrency in addition to other concurrency gotchas, read Java Concurrency inward Practice past times Brian Goetz, 1 of the most respected majority on Java concurrency.

And, if you lot desire to read to a greater extent than virtually blueprint patterns, item virtually Singleton pattern alongside examples from game development, attempt Game blueprint patterns past times Robert Nystrom, 1 of the interesting majority I read this year.

How To Honour Highest Repeating Give-And-Take From A Text File Inwards Coffee - Give-And-Take Count Problem

How to detect the give-and-take too their count from a text file is precisely about other often asked coding enquiry from Java interviews. The logic to solve this work is similar to what nosotros accept seen inwards how to detect duplicate words inwards a String. In the get-go mensuration you lot demand to construct a give-and-take Map past times reading contents of a text File. This Map should comprise give-and-take every bit a primal too their count every bit value. Once you lot accept this Map ready, you lot tin precisely variety the Map based upon values. If you lot don't know how to variety a Map on values, run into this tutorial first. It volition learn you lot past times sorting HashMap on values. Now getting primal too value inwards sorted should survive easy, but retrieve HashMap doesn't maintain order, thence you lot demand to role a List to proceed the entry inwards sorted order. Once you lot got this list, you lot tin precisely loop over the list too impress each primal too value from the entry. This way, you lot tin besides create a tabular array of words too their count inwards decreasing order.  This work is sometimes besides asked every bit to impress all give-and-take too their count inwards tabular format.

How to detect highest repeated give-and-take from a file

Here is the Java plan to detect the duplicate give-and-take which has occurred maximum lay out of times inwards a file. You tin besides impress frequency of give-and-take from highest to lowest because you lot accept the Map, which contains give-and-take too their count inwards sorted order. All you lot demand to create is iterate over each entry of Map and impress the keys too values.



Most of import business office of this solution is sorting all entries. Since Map.Entry doesn't implement the Comparable interface, nosotros demand to write our ain custom Comparator to variety the entries. If you lot await at my implementation, I am comparison entries on their values because that's what nosotros want. Many programmer says that why non role the LinkedHashMap class? but remember, the LinkedHashMap shape keeps the keys inwards sorted order, non the values. So you lot demand this exceptional Comparator to compare values too shop them inwards List.

Here is i approach to solve this work using map-reduce technique:

Java Program to Print give-and-take too their count from File

import java.io.BufferedReader; import java.io.DataInputStream; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.util.ArrayList; import java.util.Collections; import java.util.Comparator; import java.util.HashMap; import java.util.List; import java.util.Map; import java.util.Map.Entry; import java.util.Set; import java.util.StringTokenizer; import java.util.regex.Pattern; /**  * Java plan to detect count of repeated words inwards a file.  *  * @author  */ public class Problem {      public static void main(String args[]) {         Map<String, Integer> wordMap = buildWordMap("C:/temp/words.txt");         List<Entry<String, Integer>> listing = sortByValueInDecreasingOrder(wordMap);         System.out.println("List of repeated give-and-take from file too their count");         for (Map.Entry<String, Integer> entry : list) {             if (entry.getValue() > 1) {                 System.out.println(entry.getKey() + " => " + entry.getValue());             }         }     }      public static Map<String, Integer> buildWordMap(String fileName) {         // Using diamond operator for create clean code         Map<String, Integer> wordMap = new HashMap<>();         // Using try-with-resource contestation for automatic resources management         try (FileInputStream fis = new FileInputStream(fileName);                 DataInputStream dis = new DataInputStream(fis);                 BufferedReader br = new BufferedReader(new InputStreamReader(dis))) {             // words are separated past times whitespace             Pattern designing = Pattern.compile("\\s+");             String describe = null;             while ((line = br.readLine()) != null) {                 // create this if instance sensitivity is non required i.e. Java = java                 describe = line.toLowerCase();                 String[] words = pattern.split(line);                 for (String give-and-take : words) {                     if (wordMap.containsKey(word)) {                         wordMap.put(word, (wordMap.get(word) + 1));                     } else {                         wordMap.put(word, 1);                     }                 }             }         } catch (IOException ioex) {             ioex.printStackTrace();         }         return wordMap;     }      public static List<Entry<String, Integer>> sortByValueInDecreasingOrder(Map<String, Integer> wordMap) {         Set<Entry<String, Integer>> entries = wordMap.entrySet();         List<Entry<String, Integer>> listing = new ArrayList<>(entries);         Collections.sort(list, new Comparator<Map.Entry<String, Integer>>() {             @Override             public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2) {                 return (o2.getValue()).compareTo(o1.getValue());             }         });         return list;     } }  Output: List of repeated give-and-take from file too their count its => 2 of => 2 programming => 2 coffee => 2 linguistic communication => 2

Things to note

If you lot writing code on interviews brand certain they are production lineament code, which agency you lot must grip every bit many errors every bit possible, you lot must write unit of measurement tests, you lot must comment the code too you lot create proper resources management. Here are twosome of to a greater extent than points to remember:

1) Close files too streams i time you lot are through amongst it, run into this tutorial acquire correct way to closed the stream. If you lot are inwards Java 7, precisely role try-with-resource statement.

2) Since the size of the file is non specified, the interviewer may grill you lot on cases similar What happens if the file is large? With a large file, your plan volition run out of retention too throw java.lang.OutOfMemory: Java Heap space. One solution for this is to create this occupation inwards chunk e.g. get-go read 20% content, detect maximum repeated give-and-take on that, thence read adjacent 20% content too detect repeated maximum past times taking the previous maximum inwards consideration. This way, you lot don't demand to shop all words inwards retention too you lot tin procedure whatever arbitrary length file.

3) Alway role Generics for type-safety.


That's all on how to detect repeated give-and-take from a file too impress their count. You tin apply the same technique to detect duplicate words inwards a String. Since forthwith you lot accept a sorted listing of words too their count, you lot tin besides detect the maximum, minimum or repeated words which has counted to a greater extent than than the specific number.

Further Learning
The Coding Interview Bootcamp: Algorithms + Data Structures
Data Structures too Algorithms: Deep Dive Using Java
Algorithms too Data Structures - Part 1 too 2