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| Core java - Interview Questions and Answers for 'Fidelity' - 7 question(s) found - Order By Newest | ||||
 Advanced level question. Frequently asked in High end product companies. Frequently asked in Google , Cognizant and Deloitte ( Based on 2 feedback ) | ||||
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| 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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 Discuss Correct / Improve  java oops string string class immutable immutability advanced  Asked in 39 Companies  expert  frequent | ||||
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| Very frequently asked in different variations. Frequently asked in Deloitte ( 2 feedback ) , HCL Tech ( 3 feedback ), TCS and Coginizant (CTS) | ||||
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| 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 | ||||
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| Discuss Correct / Improve java string class string stringbuilder stringbuffer String vs StringBuffer String vs StringBuilder String vs StringBuilder vs StringBuffer StringBuffer vs stringBuilder Asked in 29 Companies basic frequent | ||||
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| Ans. OOPs or Object Oriented Programming is a Programming model which is organized around Objects instead of processes. Instead of a process calling series of processes, this model stresses on communication between objects. Objects that all self sustained, provide security by encapsulating it's members and providing abstracted interfaces over the functions it performs. OOP's facilitate the following features 1. Inheritance for Code Reuse 2. Abstraction for modularity, maintenance and agility 3. Encapsulation for security and protection 4. Polymorphism for flexibility and interfacing | ||||
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| Discuss Correct / Improve oops oops features Asked in 260 Companies basic frequent | ||||
| Frequently asked in Infosys India | ||||
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| 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. | ||||
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| Discuss Correct / Improve java oops string string class string pool heap memory Asked in 31 Companies intermediate frequent | ||||
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| Very Frequently asked to fresh graduates and less experienced. Favorite question in Walk in drives. Frequently asked in Indian Services companies. | ||||
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| Ans. Overloading - Similar Signature but different definition , like function overloading. Overriding - Overriding the Definition of base class in the derived class. | ||||
| Sample Code for overloading Sample Code for overriding | ||||
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| Discuss Correct / Improve java oops overloading overriding oops concepts basic interview question overloading vs overriding Asked in 86 Companies basic frequent | ||||
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| Very frequently asked in HCL Tech ( Based of 4 inputs ) | ||||
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| 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); } | ||||
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| Discuss Correct / Improve java string reverse stringbuffer string class code Asked in 6 Companies frequent | ||||
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| Ans. ConcurrentMap is an interface and it is a member of the Java Collections Framework. It represents a Map that is capable of handling concurrent access to it without affecting the consistency of entries in a map. ConcurrentMap interface present in java.util.concurrent package. HashMap operations are not synchronized, while Hashtable provides synchronization. Though Hashtable is thread-safe, it is not very efficient. To solve this issue, the Java Collections Framework introduced ConcurrentMap in Java 1.5. | ||||
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| Discuss Correct / Improve Concurrent Interface java.util.concurrent Java 8 Concurrency java concurrency java 8 Asked in 1 Companies | ||||
Which of the following class creates mutable objects ?
