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Core java - Interview Questions and Answers for 'Deloitte' - 25 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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Like 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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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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Like Discuss Correct / Improve  collections   java   data structures   arraylist   linkedlist   arraylist vs linkedlist Asked in 61 Companies Basic   frequent | ||||
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Basic and Very Frequently asked. | ||||
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Ans. Polymorphism means the condition of occurring in several different forms. Polymorphism in Java is achieved in two manners 1. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas 2. Dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding. | ||||
Sample Code for overloading Sample Code for overriding | ||||
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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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Frequently asked in high end product companies. Frequently asked in Deloitte. | ||||
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Ans. https://medium.com/javarevisited/internal-working-of-hashmap-in-java-97aeac3c7beb#:~:text=HashMap%20internally%20uses%20HashTable%20implementation,the%20entries%20into%20the%20map. | ||||
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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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Frequently asked at HCL Technologies ( Based on 3 feedback ) | ||||
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Ans. Checked exceptions are the exceptions for which compiler throws an errors if they are not checked whereas unchecked exceptions are caught during run time only and hence can't be checked. | ||||
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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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Like Discuss Correct / Improve  serialization   java   oops   static   static variables Asked in 1 Companies intermediate   rare | ||||
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Ans. Vectors are synchronized whereas Array lists are not. | ||||
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Ans. It in Java is used to indicate that a field should not be serialized. | ||||
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Like 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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Ans. Iterators in java are used to iterate over the Collection objects. Fail-Fast iterators immediately throw ConcurrentModificationException if there is any addition, removal or updation of any element. Fail-Safe iterators don't throw any exception if a collection is structurally modified while iterating over it. This is because, they operate on the clone of the collection and not on the original collection. | ||||
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Like Discuss Correct / Improve  ail fast   fail saf Asked in 9 Companies intermediate | ||||
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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 | ||||
Usually asked to entry level software developers. | ||||
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Ans. public static void main(String[] args) { int num1 = 1; int num2 = 2; num1 = num1^num2; num2 = num1^num2; num1 = num1^num2; System.out.print("num1 = " + num1 +", num2 = "+num2); } | ||||
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Ans. No | ||||
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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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Ans. No, results in exception. | ||||
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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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Ans. 1. Switching Overheads - Even though multi threading aims at improving performance by reducing the wait time and hence improving overall throughput, there is a cost of switching resources between threads and sometime this cost can surpass the benefits if there isnt much wait for IO or external communication. 2. Debugging is hard with multi threaded code. 3. Deadlock - Execution of multi threaded code many a times lead to deadlock due to shared resources. | ||||
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Very frequently asked. | ||||
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Ans. Synchronize is used to achieve mutual exclusion i.e at one time, the segment of the code, method that has been declared synchronized should be executed by single thread only and hence the lock needs to be retrieved before executing the segment and then released. | ||||
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Ans. An Exception in java is the occurrence during computation that is anomalous and is not expected. Exception handling is the mechanism which is used to handle such situations. | ||||
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Ans. Abstract class is one of the facility for achieving abstraction in Java. | ||||
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Ans. public static void printTriagle(int n) { // outer loop to handle number of rows // n in this case for (int i=0; i1; j--) { // printing spaces System.out.print(" "); } // inner loop to handle number of columns // values changing acc. to outer loop for (int j=0; j<=i; j ) { // printing stars System.out.print("* "); } // ending line after each row System.out.println(); } } // Driver Function public static void main(String args[]) { int n = 5; printTriagle(n); } | ||||
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Ans. Using comparable and comparator and sorted collections like TreeSet or TreeMap. or use stream api from java 8 onwards which internally refers to comparable and comparator through lambda expressions | ||||
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Like Discuss Correct / Improve  sort  sorting  comprator  comparable  treeset  treemap  sorting collections Asked in 1 Companies Basic   frequent | ||||