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Ans. Keep it as a Abstract Class if its a "Is a" Relationsship and should do subset/all of the functionality. Keep it as Interface if its a "Should Do" relationship. | ||||
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Like Discuss Correct / Improve  java   oops   abstract classes   interfaces   advanced Asked in 3 Companies | ||||
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Ans. Collections class is a utility class having static methods for doing operations on objects of classes which implement the Collection interface. For example, Collections has methods for finding the max element in a Collection. | ||||
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Like Discuss Correct / Improve  java   collections   collections class   collection interface   basic interview question Asked in 6 Companies basic   frequent | ||||
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Ans. Class loaders are hierarchical. The very first class is specially loaded with the help of static main() method declared in your class. All the subsequently loaded classes are loaded by the classes, which are already loaded and running. | ||||
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Ans. static loading - Classes are statically loaded with Java new operator. dynamic class loading - Dynamic loading is a technique for programmatically invoking the functions of a class loader at run time. Class.forName (Test className); | ||||
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Like Discuss Correct / Improve  java   jvm   memory management   class loaders  classloaders   static class loading   static loading   dynamic class loading   dynamic loading Asked in 2 Companies expert   frequent | ||||
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Ans. Collections are re-sizable in nature. We can increase or decrease the size as per recruitment. Collections can hold both homogeneous and heterogeneous data's. Every collection follows some standard data structures. Collection provides many useful built in methods for traversing,sorting and search. | ||||
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Like Discuss Correct / Improve  java   collections   collections classes   advantages of collections over arrays   collections vs arrays   basic interview question Asked in 6 Companies basic   frequent | ||||
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Ans. private static boolean isPalindrome(String str) { if (str == null) return false; StringBuilder strBuilder = new StringBuilder(str); strBuilder.reverse(); return strBuilder.toString().equals(str); } | ||||
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Like Discuss Correct / Improve  java   string   stringbuilder   stringbuilder   string class   code   palindrome Asked in 38 Companies Basic   frequent | ||||
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Ans. private static String removeChar(String str, char c) { | ||||
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Like Discuss Correct / Improve  java   string   string class   code   write code | ||||
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Ans. Since String is immutable, its hashcode is cached at the time of creation and it doesnt need to be calculated again. This makes it a great candidate for key in a Map and its processing is fast than other HashMap key objects. This is why String is mostly used Object as HashMap keys. | ||||
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Like Discuss Correct / Improve  java   string class   string   immutable  immutability   hashmap   immutable  immutability   hashcode   hash code   advanced Asked in 2 Companies expert   frequent | ||||
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Ans. intern() method keeps the string in an internal cache that is usually not garbage collected. Moreover provide reference for scp object for corresponding string object present in heap memory. | ||||
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Like Discuss Correct / Improve  java   string class   string   intern method   garbage collection   advanced Asked in 2 Companies expert | ||||
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Ans. substring method would build a new String object keeping a reference to the whole char array, to avoid copying it. Hence you can inadvertently keep a reference to a very big character array with just a one character string. | ||||
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Like Discuss Correct / Improve  java   string class   string   substring   memory leaks   jvm   memory management   advanced   architecture   technical architect   technical lead expert | ||||
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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Like Discuss Correct / Improve  java   string   reverse   stringbuffer   string class   code Asked in 6 Companies   frequent | ||||
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Ans. new operator is used to statically create an instance of object. newInstance() is used to create an object dynamically ( like if the class name needs to be picked from configuration file ). If you know what class needs to be initialized , new is the optimized way of instantiating Class. | ||||
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Ans. 1. Entity classes should have default constructor. 2. Entity classes should be declared non final. 3. All elements to be persisted should be declared private and should have public getters and setters in the Java Bean style. 4. All classes should have an ID that maps to Primary Key for the table. | ||||
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Like Discuss Correct / Improve  hibernate   entity classes hibernate | ||||
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Ans. Abstraction is provided in Java by following ways - Coding to the ( Interfaces / Abstract Classes ) or contracts By Encapsulating details within classes and exposing the minimal Door ( few public methods ) | ||||
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Like Discuss Correct / Improve  java   oops concepts   abstraction   interfaces   abstract class   encapsulation  object oriented programming (oops)  oops concepts Asked in 3 Companies basic   frequent | ||||
Ans. Constructors , Classes ( Outer ) , Interfaces , Local variables , Inner Class methods and instance variables. | ||||
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Like Discuss Correct / Improve  oops   java   static   nested classes   static nested classes | ||||
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Ans. A trigger is a special kind of stored procedure that automatically gets executed upon an event in the database server. | ||||
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Ans. When a Table Join itself , it's a Self Join. For example - we like to know the pair of department names where first dept has lesser employees than the later. Select D1.name , D2.name from Dept D1, Dept D2 where D1.employee_count < D2.employee_count | ||||
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Like Discuss Correct / Improve  sql  joins  self join  self-join  Pair of employee names with first having lesser salary than later  Pair of department names where first dept has lesser employees than the later Asked in 26 Companies basic   frequent | ||||
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Ans. System is a class within java.lang package that contains several useful class fields and methods. It cannot be instantiated and hence can use only statically.even in this case this has been used statically i.e with class name itself and without creating an instance. out is the static reference of Printstream declared as following in the System Class - public final static PrintStream out = null; println is the method of PrintStream class. | ||||
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Like Discuss Correct / Improve  System class  Streams  Input Output  println Asked in 1 Companies basic   frequent | ||||
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Ans. Yes, we can do that. Compiler wont complain. But using object reference we can only access methods which have been defined for object class i.e clone(), equals(), hashCode(), toString() etc. We cannot access methods defined in String class or in any class in hierarchy between String and Object. For example - we cannot do obj.append("abc") as it will now give compile time error. | ||||
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Like Discuss Correct / Improve  object initialization  object declaration   runtime polymorphism  object oriented programming (oops)  oops concepts | ||||
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Ans. wait and notify are declared final in object class and hence cannot be overridden. | ||||
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Ans. Though var args are used rarely but they are pretty useful if a method is expected to receive variable number of arguments. For example - it's pretty useful for the main method as the caller has the flexibility to provide arguments in infinite ways.It provides a convenience and flexibility to the caller. | ||||
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Like Discuss Correct / Improve  var args  methods  method declarations  functions | ||||
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Ans. Abstraction is a process of hiding the implementation details and describing only the functionality to the user. | ||||
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Like Discuss Correct / Improve  bstraction  oops concepts  oops principle Asked in 22 Companies | ||||
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Ans. No | ||||
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Like Discuss Correct / Improve  abstract class   multiple inheritance  object oriented programming (oops)  oops concepts Asked in 2 Companies | ||||
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Ans. Yes, to a certain extent. But the objective for Final class could be beyond just enforcing composition as certain classes might have been created without inheritance or composition in mind. | ||||
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Like Discuss Correct / Improve  final class   composition  object oriented programming (oops)  oops concepts  inheritance  object oriented programming (oops)  oops concepts  composition  object oriented programming (oops)  oops concepts vs inheritance  object oriented programming (oops)  oops concepts expert | ||||
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Ans. 1. Enforcing composition over inheritance 2. Restricting overriding of certain methods 3. Final methods are faster than regular instance methods 4. Enforcing Immutability | ||||
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Like Discuss Correct / Improve  final class   reasons for final class   restricting inheritance  object oriented programming (oops)  oops concepts expert | ||||
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Ans. Base Class is a relative term used to signify the Parent class in Parent - Child or Base - derived relationship. Derived Class is a relative term used to signify the Child class in Parent - Child or Base - derived relationship. Abstract Class is a class that is not allowed to be instantiated and hence can serve only a base class for it's usage. Concrete Class is the class which is supposed to be instantiated and hence provide definition for all implementing interface methods and extending abstract methods. | ||||
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Like Discuss Correct / Improve  Base Class   Derived Class   Abstract Class   Concrete Class | ||||
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Ans. Multiple servlets serving the request in chain. | ||||
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Like Discuss Correct / Improve  java   web application   servlets Asked in 1 Companies   rare | ||||
Very frequently asked. Usually asked in this format or as difference with interfaces / concrete classes. | ||||
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Ans. Abstract class is the class that is not supposed to be instantiated. The purpose of the class to only have extension to the derived class. | ||||
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Like Discuss Correct / Improve  abstract class Asked in 6 Companies basic   frequent | ||||
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Ans. They both represent the long primitive type. They are exactly the same. | ||||
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Like Discuss Correct / Improve  java   data types   long.Class   long.TYPE   advanced expert   rare | ||||
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Ans. Sometime we just need classes or class objects just to be used as part of a particular class or objects. Making them non nested won't make any difference as far as functionality is concerner but making them Nested provide a level of convenience and protection fro, being used anywhere else. Moreover it helps reducing the Code. | ||||
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