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Interview Questions and Answers for 'Prokarma' - 6 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.

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   Like         Discuss         Correct / Improve     java   oops   string   string class   immutable  immutability   advanced     Asked in 35 Companies      expert        frequent

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  Q2. Can we have null keys in TreeMap ?Core Java
Admin
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Ans. No, results in exception.

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   Like         Discuss         Correct / Improve     java   collections   treemap     Asked in 6 Companies      Basic        frequent


 Q3. What is a ConcurrentHashMap ?Core Java
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Ans. ConcurrentHashMap is a hashMap that allows concurrent modifications from multiple threads as there can be multiple locks on the same hashmap.

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   Like         Discuss         Correct / Improve     java   collections   hashmap   map   concurrenthashmap   concurrenthashmap  concurrency   general electric   ge     Asked in 32 Companies        rare


  Q4. What is lazy fetching in Hibernate ?Hibernate
Admin
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Ans. Lazy fetching is the technique of not loading the child objects when parent objects are loaded. By default Hibernate does not load child objects. One can specify whether to load them or not while doing the association.

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   Like         Discuss         Correct / Improve     hibernate   lazy fetching   architecture     Asked in 11 Companies        frequent

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 Q5. What is ConcurrentModificationException ?Core Java
Admin
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Ans. This is the exception that is thrown when we try to modify the non concurrent collection class while iterating through it.

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


 Q6. What is Dirty read in Database Transactions ?Database2016-11-14 13:11:55

Ans. A dirty read occurs when a transaction is allowed to read data from a row that has been modified by another running transaction but not yet committed.

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   Like         Discuss         Correct / Improve     database transaction     Asked in 8 Companies




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