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| Ans. No. Only Object and its members are serialized. Static variables are shared variables and doesn't correspond to a specific object. | ||||
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 Discuss Correct / Improve  serialization java oops static static variables  Asked in 1 Companies  intermediate  rare | ||||
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 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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| Ans. Vectors are synchronized whereas Array lists are not. | ||||
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| Discuss Correct / Improve java basic interview question vector arraylist collections synchronization vector vs arraylist Asked in 35 Companies basic frequent | ||||
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| Ans. It in Java is used to indicate that a field should not be serialized. | ||||
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| Discuss Correct / Improve java oops serialization transient java keywords Asked in 39 Companies intermediate frequent | ||||
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| Very Frequently asked. Usually asked along with String Class related questions. | ||||
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| Ans. Class using which only immutable (objects that cannot be changed after initialization) objects can be created. | ||||
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| Discuss Correct / Improve java oops immutable immutability immutable immutability class string class basic interview question Asked in 18 Companies Basic frequent | ||||
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| Ans. We can make a class immutable by 1. Making all methods and variables as private. 2. Setting variables within constructor. Public Class ImmutableClass{ private int member; ImmutableClass(int var){ member=var; } } and then we can initialize the object of the class as ImmutableClass immutableObject = new ImmutableClass(5); Now all members being private , you cant change the state of the object. | ||||
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| Discuss Correct / Improve java oops immutable immutability immutable immutability class technical lead Asked in 5 Companies intermediate 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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| Advanced level question. Recently asked in few Indian service companies ( Based on 3 inputs ) | ||||
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| Ans. Bootstrap - Loads JDK internal classes, java.* packages. Extensions - Loads jar files from JDK extensions directory - usually lib/ext directory of the JRE System - Loads classes from system classpath. | ||||
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| Discuss Correct / Improve java jvm memory management class loaders bootstrap extensions system classloaders advanced technical lead technical architect Asked in 7 Companies | ||||
| Very Frequently asked. Favorite question in walkins and telephonic interviews. Usually among first few questions. Asked in different variants. Must know for intermediate and expert professionals.Among Top 10 frequently asked questions. | ||||
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| Ans. A Class must override the hashCode method if its overriding the equals method. | ||||
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| Discuss Correct / Improve java collections hashcode hash code equals collections Asked in 44 Companies intermediate frequent | ||||
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| Ans. No, results in exception. | ||||
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| Discuss Correct / Improve java collections treemap Asked in 6 Companies Basic frequent | ||||
| Very frequently asked. Favorite question in Walk in Drive of many Indian service companies. | ||||
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| Ans. Underlying data structure for ArrayList is Array whereas LinkedList is the linked list and hence have following differences - 1. ArrayList needs continuous memory locations and hence need to be moved to a bigger space if new elements are to be added to a filled array which is not required for LinkedList. 2. Removal and Insertion at specific place in ArrayList requires moving all elements and hence leads to O(n) insertions and removal whereas its constant O(1) for LinkedList. 3. Random access using index in ArrayList is faster than LinkedList which requires traversing the complete list through references. 4. Though Linear Search takes Similar Time for both, Binary Search using LinkedList requires creating new Model called Binary Search Tree which is slower but offers constant time insertion and deletion. 5. For a set of integers you want to sort using quicksort, it's probably faster to use an array; for a set of large structures you want to sort using selection sort, a linked list will be faster. | ||||
| Sample Code for ArrayList Sample Code for LinkedList | ||||
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| Discuss Correct / Improve collections java data structures arraylist linkedlist arraylist vs linkedlist Asked in 61 Companies Basic frequent | ||||
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| Frequently asked question in companies using Hibernate. | ||||
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| Ans. It's a feature to lazily initialize dependencies , relationship and associations from the Database. Any related references marked as @OneToMany or @ManyToMany are loaded lazily i.e when they are accessed and not when the parent is loaded. | ||||
| Sample Code for Lazy Initialization | ||||
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| Discuss Correct / Improve hibernate lazy loading hibernate lazy initialization hibernate architecture Asked in 77 Companies Basic frequent | ||||
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| Very frequently asked. Usually followed by questions related to private constructor and synchronized access. Frequently asked in JPMorgan and TCS (Based on 2 feedback) | ||||
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| Ans. http://www.buggybread.com/2014/03/java-design-pattern-singleton-interview.html | ||||
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| Discuss Correct / Improve java design pattern singleton at&t ebay fidelity india united healthcare india Asked in 46 Companies intermediate frequent | ||||
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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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| Discuss Correct / Improve java collections concurrentmodificationexception exception concurrency Asked in 14 Companies intermediate | ||||
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| Ans. Exception thrown by the application is we try to access an element using an index which is not within the range of array i.e lower than 0 or greater than the size of the array. | ||||
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| Discuss Correct / Improve java exceptions arrayindexoutofboundexception Asked in 1 Companies | ||||
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| Ans. Jar is Java Archieve i.e compressed Class or Class / Java files. War comprises of compressed Servlet class files,JSP FIles,supporting files, GIF and HTML files. Ear comprise of compressed Java and web module files ( was files ). | ||||
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| Discuss Correct / Improve java j2ee jar web development war ear build management release management Asked in 12 Companies basic frequent | ||||
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| Ans. It is a continuous integration tool written in Java. | ||||
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| Discuss Correct / Improve java jenkins Asked in 6 Companies Basic frequent | ||||
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Which of the following is true ?
