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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 | ||||
Ans. No the static block won't get executed as the referenced variable in the Test class is final. Compiler replaces the content of the final variable within Demo.main method and hence actually no reference to Test class is made. | ||||
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Like Discuss Correct / Improve  java   oops   static   static block   final variable | ||||
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Ans. It will create the file myfile.txt in the current directory. | ||||
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Like Discuss Correct / Improve  java   io   file   fileio   coding   code   file handling | ||||
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Ans. The purpose of comparator interface is to compare objects of the same class to identify the sorting order. Sorted Collection Classes ( TreeSet, TreeMap ) have been designed such to look for this method to identify the sorting order, that is why class need to implement Comparator interface to qualify its objects to be part of Sorted Collections. | ||||
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Like Discuss Correct / Improve  java   collections   treemap   treeset   comparator Asked in 2 Companies Intermediate | ||||
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Ans. 1. Methods can participate in runtime polymorphism whereas member variables cannot. For example - Vehicle vehicle = new Car(); car.getObjVariable();// will return variable defined in Car whereas car.variable will return the variable from Car class irrespective of the object it holds. 2. Validations can be performed before setting the variables. 3. If the input format changes or some other value or calculated value needs to be returned , that can be absorbed by making change ( wrapping ) in the setter and getter. By this the call to method from outside or interface to the object will remain the same. | ||||
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Like Discuss Correct / Improve  java   beans   getter   setter | ||||
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Ans. Yes, but the overloaded main methods without single String[] argument doesn't get any special status by the JVM. They are just another methods that needs to be called explicitly. | ||||
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Like Discuss Correct / Improve  java   main method   overloading   yes-no Asked in 6 Companies intermediate   frequent | ||||
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Ans. Tree Set will sort the Values in the order in which Enum constants are declared. | ||||
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Like Discuss Correct / Improve  java   collections   set   treeset   enum   sorting   technical lead | ||||
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Ans. No. compareTo method is declared final for the Enumerations and hence cannot be overriden. This has been intentionally done so that one cannot temper with the sorting order on the Enumeration which is the order in which Enum constants are declared. | ||||
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Like Discuss Correct / Improve  java   compareto   final methods   enum   enumeration expert | ||||
Very Frequently asked. | ||||
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Ans. throw is used to re throw an exception.throws is used to declare that the method throws the respective exceptions.try block is used to identify if the respective block has thrown any exception.catch is used to catch the exception that has been thrown by the respective try block. | ||||
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Like Discuss Correct / Improve  java   exception handling   throw   throws   try   catch Asked in 5 Companies basic   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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Like Discuss Correct / Improve  java   collections   concurrentmodificationexception   exception  concurrency Asked in 14 Companies intermediate | ||||
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Ans. It's a choice to be made whether to use first approach ( Thread class ) or second approach ( runnable interface ) by the programmer. The second facility has been given for cases where your class is already extending some parent class and hence cannot extend another class ( for Thread ) as Java doesn't allow multiple inheritance. | ||||
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Like Discuss Correct / Improve  java   threads   multithreading   runnable interface  concurrency | ||||
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Ans. BlockingQueue is a Queue that supports operations that wait for the queue to become non-empty when retrieving and removing an element, and wait for space to become available in the queue when adding an element. | ||||
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Like Discuss Correct / Improve  blockingqueue   collections   java   concurrent collections Asked in 10 Companies | ||||
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Ans. LinkedHashMap | ||||
Sample Code for LinkedHashMap | ||||
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Ans. Random Order | ||||
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Ans. name and argument list | ||||
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Ans. web.xml | ||||
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Ans. A no argument constructor is provided by the compiler if we declare only constructors with arguments. | ||||
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Ans. Map | ||||
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Ans. Inheritance | ||||
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Ans. svn | ||||
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Ans. static | ||||
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Like Discuss Correct / Improve  java   enum | ||||
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Ans. It could be worthy to move a method to util class if the method needs to be shared, doesn't require polymorphic behavior and need not be overridden in special cases. Don't belong to one group through is-a relationship ( You can share through parent class method ) Don't implement a specific interface ( java 8 default methods ) Doesn't involve complex computing as you will be loosing the benefit of object state with just static method. Doesn't require polymorphic behavior as static methods don't participate in runtime polymorphism. | ||||
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Like Discuss Correct / Improve  utility classes   util classes   static methods   application design   rare | ||||
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Ans. 1. Method local variables - These are declared and defined within a method ( instance or static methods ) and their scope is limited to the method itself. They are destructed once the execution of method completes. They are stored in stack memory. 2. Instance variables - These are declared as non static variables as part of the class.They are initialized as part of object creation ( constructor ) and are destructed by java's garbage collection mechanism and hence stored in heap. 3. Static variables - These are declared with the static keyword and are part of the class. They are initialized at the time of class loading and are destructed by java's garbage collection mechanism and hence stored in heap. | ||||
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Ans. class A { void test() { System.out.println("test() method"); } } class B { void test() { System.out.println("test() method"); } } Suppose if Java allows multiple inheritance like this, class C extends A, B { } A and B test() methods are inheriting to C class. So which test() method C class will take? As A & B class test() methods are different , So here we would Facing Ambiguity. | ||||
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Like Discuss Correct / Improve  multiple inheritance  object oriented programming (oops)  oops concepts  diamond problem Asked in 20 Companies basic   frequent | ||||
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This question was recently asked at 'Wayfair'.This question is still unanswered. Can you please provide an answer. | ||||
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Like Discuss Correct / Improve   Asked in 1 Companies | ||||
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This question was recently asked at 'Ariba'.This question is still unanswered. Can you please provide an answer. | ||||
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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. public class BuggyBread { public static void main(String args[]) { for(int x=1;x<=5;x++){ for(int y=1;y<=x;y++){ System.out.print("*"); } System.out.println(""); } for(int x=5;x>=1;x--){ for(int y=1;y<=x;y++){ System.out.print("*"); } System.out.println(""); } } } | ||||
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Ans. Such a class still can have member elements which can be inherited and hence facilitate code reuse. Moreover Abstract class can have non final static elements whereas interfaces are only allowed to have static final elements. | ||||
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Like Discuss Correct / Improve  abstract class   interfaces Asked in 2 Companies Basic | ||||
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Ans. No. Because java internally treats var args as arrays and hence both method declarations will generate the same byte code and hence would result in ambiguity while determining call binding. | ||||
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Like Discuss Correct / Improve  var args  methods  functions   method declaration  scjp  ocjp | ||||