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Core java - Interview Questions and Answers for 'Bayatree infocom' - 2 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 37 Companies      expert        frequent

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Related Questions

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 How does making string as immutable helps with securing information ? How does String Pool pose a security threat ?
 How is string object immutable if we can concat a string to it ?
  What is an Immutable Object ?
  What is an immutable class ?
  How to implement an immutable class ?
  Does Declaring an object "final" makes it immutable ?
  What are stateless objects ? How are they different from immutable objects ? Which of these two is thread safe ?
  What are advantages of stateless and / or immutable objects ?


Frequently asked in all types of companies especially Indian Services companies. Frequently asked in CTS (Based on 2 feedback)
  Q2. What is the use of hashcode in Java ?Core Java
Anonymous
Ans. Hashcode is used for bucketing in Hash implementations like HashMap, HashTable, HashSet etc. The value received from hashcode() is used as bucket number for storing elements. This bucket number is the address of the element inside the set/map. when you do contains() then it will take the hashcode of the element, then look for the bucket where hashcode points to and if more than 1 element is found in the same bucket (multiple objects can have the same hashcode) then it uses the equals() method to evaluate if object are equal, and then decide if contain() is true or false, or decide if element could be added in the set or not.

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   Like         Discuss         Correct / Improve     java   collections   hashcode   advanced  hashtable     Asked in 32 Companies      intermediate        frequent

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Related Questions

  Which String class does not override the equals() and hashCode() methods, inheriting them directly from class Object?
 Write a class and override the equals and hashcode method ?




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