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|Java - Interview Questions and Answers|
|Advanced level question. Frequently asked in High end product companies. Frequently asked in Cognizant ( Based on 2 feedbacks )|
|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.|
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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Try 4 Question(s) Test
|Why Char array is preferred over String for storing password?|
|What is an Immutable Object ?|
|What is an immutable class ?|
|How to implement an immutable class ?|
|Does Declaring an object "final" makes it immutable ?|
|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 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 ?|