Core Java - Interview Questions and Answers for 'String class' | Search Java Interview Question

Core Java - Interview Questions and Answers for 'String class' - 21 question(s) found - Order By Newest

Advanced level question. Frequently asked in High end product companies. Frequently asked in Cognizant and Deloitte ( Based on 2 feedback )

Q1. Why is String immutable in Java ?

Core Java

^Anonymous

Ans. 1. String Pool - When a string is created and if it exists in the pool, the reference of the existing string will be returned instead of creating a new object. If string is not immutable, changing the string with one reference will lead to the wrong value for the other references.

Example -

String str1 = "String1";
String str2 = "String1"; // It doesn't create a new String and rather reuses the string literal from pool

// Now both str1 and str2 pointing to same string object in pool, changing str1 will change it for str2 too

2. To Cache its Hashcode - If string is not immutable, One can change its hashcode and hence it's not fit to be cached.

3. Security - String is widely used as parameter for many java classes, e.g. network connection, opening files, etc. Making it mutable might possess threats due to interception by the other code segment.

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

_{Like Discuss Correct / Improve java oops string string class immutable advanced Barclays Jungo Cloudera Allston Man Group Prokarma Optimus Gamesys ABS TransPerfect Fidelity Deloitte Zalando Cognizant (CTS) Zeta Interactive SuccessFactors
EchoStar InterGlobe Technologies HCL Technologies Intuit JP Morgan Optimus Information Faichi Solutions Blip Adobe Subex Limited Remo Software Allstate IBM Bizmatics Bytecode Cyber Security Calsoft Systems IDS Infotech Nakisa expert frequent}

Try 4 Question(s) Test

Very frequently asked in different variations. Frequently asked in Deloitte ( 2 feedback ) , HCL Tech ( 3 feedback ) and Coginizant (CTS)

Q2. Explain the scenerios to choose between String , StringBuilder and StringBuffer ?

or

What is the difference between String , StringBuilder and StringBuffer ?

Core Java

^Anonymous

Ans. If the Object value will not change, use String Class because a String object is immutable.

If the Object value can change and will only be modified from a single thread, use StringBuilder because StringBuilder is unsynchronized(means faster).

If the Object value may change, and can be modified by multiple threads, use a StringBuffer because StringBuffer is thread safe(synchronized).

Sample Code for String

Sample Code for StringBuffer

Sample Code for StringBuilder

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

_{Like Discuss Correct / Improve java string class string stringbuilder stringbuffer Cognizant (CTS) San Jose State University (SJSU) HCL Technologies Deloitte Sophos Hitachi JPMorgan Chase IBM Kony Labs Keystone ebay TIAA Financial Services Ancestry Rakuten basic frequent}

Try 3 Question(s) Test

Q3. What are different ways to create String Object? Explain.

Core Java

^{Admin
info@buggybread.com}

Ans. When we create a String using double quotes, JVM looks in the String pool to find if any other String is stored with same value. If found, it just returns the reference to that String object else it creates a new String object with given value and stores it in the String pool.

When we use new operator, JVM creates the String object but dont store it into the String Pool. We can use intern() method to store the String object into String pool or return the reference if there is already a String with equal value present in the pool.

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

_{Like Discuss Correct / Improve java string class string jvm memory management string pool GuideWire NTT Data Fractal Analytics Accolite basic frequent}

Try 3 Question(s) Test

Q4. Why Char array is preferred over String for storing password?

Core Java

^{Admin
info@buggybread.com}

Ans. String is immutable in java and stored in String pool. Once it's created it stays in the pool until unless garbage collected, so even though we are done with password it's available in memory for longer duration and there is no way to avoid it. It's a security risk because anyone having access to memory dump can find the password as clear text.

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

_{Like Discuss Correct / Improve java string class string immutable string pool garbage collection advanced General Motors Amura Marketing Technologies Bloomberg Innovive Expert}

Q5. What will this code print ?

String a = new String ("TEST");
String b = new String ("TEST");
if(a == b) {
System.out.println ("TRUE");
} else {
System.out.println ("FALSE");
}

Core Java

^Anonymous

Ans. FALSE. == operator compares object references, a and b are references to two different objects, hence the FALSE. .equals method is used to compare string object content.

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

_{Like Discuss Correct / Improve string string class java == object references coding Capgemini HCL Technologies basic frequent}

Try 1 Question(s) Test

Q6. What is a String Pool ?

Core Java

^Anonymous

Ans. String pool (String intern pool) is a special storage area in Java heap. When a string is created and if the string already exists in the pool, the reference of the existing string will be returned, instead of creating a new object and returning its reference.

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

_{Like Discuss Correct / Improve java oops string string class string pool heap memory SAS Institute Ariba GuideWire Harbinger Oracle Virtusa Knoa Polaris GuideWire HCL Technologies Tata Consultancy (TCS) Infosys Technologent MphasiS Harbinger Group Kony Evergent NTT Data VMware Markit Ariba Tech Mahindra Bureau Veritas InfoStretch PTC Software Mindtree Centre for Internet and Society (CIS) Trimax IT Infrastructure & Services intermediate frequent}

Try 2 Question(s) Test

Very Frequently asked. Usually asked along with String Class related questions.

Q7. What is an immutable class ?

Core Java

^Anonymous

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 immutable class string class basic interview question Cognizant (CTS) Hybris YuMe ebizAutos Deloitte HCL Technologies Tata Consultancy (TCS) Infosys Accenture Overstock.com Elsevier Endurance International Group SynergisticIT Verizon Capgemini Ebay Basic frequent}

Try 2 Question(s) Test

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

Q8. Difference between StringBuffer and StringBuilder ?

Core Java

^Anonymous

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 Thomson Reuters Ludia QualiTest United Health Group (UHG) Sophos JPMorgan Chase ebay Infosys Technologies Experian India HCL Technologies Symantec Tata Consultancy (TCS) Accenture Infosys Cerner Priceline basic frequent}

Try 1 Question(s) Test

Q9. Write a method to check if input String is Palindrome?

Core Java

^{Admin
info@buggybread.com}

Ans. private static boolean isPalindrome(String str) {

if (str == null)
return false;

StringBuilder strBuilder = new StringBuilder(str);

strBuilder.reverse();

return strBuilder.toString().equals(str);

}

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

_{Like Discuss Correct / Improve java string stringbuilder stringbuilder string class code palindrome HCL Technologies Hootsuite ebay Mobile Apps Company TripAdvisor Wallet Hub Groupon OpenText Airbnb Vantiv Minted LLC Boston Analytics mint.com Arista Networks Dealer.com the Zappos Family Sony PlayStation Taser Wolters Kluwer Wize Commerce Hitachi Consulting Quickr SmartBrief Liaison International Monitise Exilant Technologies Enova Wayfair Amadeus MakeMyTrip Naggaro Vudu OnDeck Capital HighRadius
thePlatform Trimax IT Infrastructure & Services Basic frequent}

Do you think these are the Best Java Frameworks ?

OpenXava

SPRING MVC

Apache Stripes

Check everything
that is Best in Java

Click Here

Q10. Write a method that will remove given character from the String?

Core Java

^{Admin
info@buggybread.com}

Ans.

private static String removeChar(String str, char c) {    

   if (str == null)        

      return null;     

   

   return str.replaceAll(Character.toString(c), "");

}

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

_{Like Discuss Correct / Improve java string string class code write code}

Q11. What does String intern() method do?

Core Java

^{Admin
info@buggybread.com}

Ans. intern() method keeps the string in an internal cache that is usually not garbage collected.

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

_{Like Discuss Correct / Improve java string class string intern method garbage collection advanced Polaris Netflix expert}

Q12. How substring() method of String class create memory leaks?

Core Java

^{Admin
info@buggybread.com}

Ans. substring method would build a new String object keeping a reference to the whole char array, to avoid copying it. Hence you can inadvertently keep a reference to a very big character array with just a one character string.

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

_{Like Discuss Correct / Improve java string class string substring memory leaks jvm memory management advanced architecture technical architect technical lead expert}

Very frequently asked in HCL Tech ( Based of 4 inputs )

Q13. Write a program to reverse a string iteratively and recursively ?

Core Java

^{Admin
info@buggybread.com}

Ans. Using String method -

new StringBuffer(str).reverse().toString();

Iterative -

public static String getReverseString(String str){
StringBuffer strBuffer = new StringBuffer(str.length);
for(int counter=str.length -1 ; counter>=0;counter--){
strBuffer.append(str.charAt(counter));
}
return strBuffer;
}

Recursive -

public static String getReverseString(String str){
if(str.length <= 1){
return str;
}
return (getReverseString(str.subString(1)) + str.charAt(0);
}

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

_{Like Discuss Correct / Improve java string reverse stringbuffer string class code HCL Technologies Exelis Mahindra Comviva Fidelity National Information Services (FIS) Genpact Digite Infotech frequent}

Q14. Which String class methods are used to make string upper case or lower case?

Core Java

^{Admin
info@buggybread.com}

Ans. toUpperCase and toLowerCase

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

_{Like Discuss Correct / Improve java string class string}

Q15. How to convert String to byte array and vice versa?

Core Java

^{Admin
info@buggybread.com}

Ans. We can use String getBytes() method to convert String to byte array and we can use String constructor new String(byte[] arr) to convert byte array to String.

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

_{Like Discuss Correct / Improve java string class string}

Q16. Why String is popular HashMap key in Java?

Core Java

^{Admin
info@buggybread.com}

Ans. Since String is immutable, its hashcode is cached at the time of creation and it doesnt need to be calculated again. This makes it a great candidate for key in a Map and its processing is fast than other HashMap key objects. This is why String is mostly used Object as HashMap keys.

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

_{Like Discuss Correct / Improve java string class string immutable hashmap immutable hashcode hash code advanced TD Bank HCL Technologies expert frequent}

Q17. What will be the output of the following code ?

String s1 = "Buggy Bread";
String s2 = "Buggy Bread";
if(s1 == s2)
System.out.println("equal 1");
String n1 = new String("Buggy Bread");
String n2 = new String("Buggy Bread");
if(n1 == n2)
System.out.println("equal 2");

Core Java

^{Admin
info@buggybread.com}

Ans. equal 1

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

_{Like Discuss Correct / Improve java string class string string pool code coding basic frequent}

Q18. Which methods of the Pattern class have equivalent methods in the String class?

Core Java

^{Admin
info@buggybread.com}

Ans. split() and macthes()

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

_{Like Discuss Correct / Improve java io string class string pattern}

Q19. How does the String Class stores the string in memory ?

Core Java

^{2016-06-14 14:33:03}

Ans. It stores the string as a character array with 2 bytes for each character.

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

_{Like Discuss Correct / Improve String String Class}

Do you think these are the Best Java Frameworks ?

OpenXava

SPRING MVC

Apache Stripes

Check everything
that is Best in Java

Click Here

Q20. How is String class unique ?

Core Java

^{2016-11-30 15:46:13}

Ans. String class is immutable as well as final. Because of these properties , String objects offer many benefits

1. String Pool - When a string is created and if it exists in the pool, the reference of the existing string will be returned instead of creating a new object. If string is not immutable, changing the string with one reference will lead to the wrong value for the other references.

Example -

String str1 = "String1";
String str2 = "String1"; // It doesnt create a new String and rather reuses the string literal from pool

// Now both str1 and str2 pointing to same string object in pool, changing str1 will change it for str2 too

2. To Cache its Hashcode - If string is not immutable, One can change its hashcode and hence its not fit to be cached.

3. Security - String is widely used as parameter for many java classes, e.g. network connection, opening files, etc. Making it mutable might possess threats due to interception by the other code segment.

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

_{Like Discuss Correct / Improve immutable immutability String string class Overstock.com}

Q21. Which method of String class is used to convert Boolean to String ?

Core Java

^{2016-12-17 11:00:44}

Ans. toString() is an overloaded method of String class that is used to convert many data types to String, Boolean being one of them.

toString(Boolean bool)

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

_{Like Discuss Correct / Improve String String class Boolean Techurate Systems Basic}

Search Interview Questions

Help us and Others Improve. Please let us know the questions asked in any of your previous interview.