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Interview Questions and Answers - Order By Rating | ||||
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Ans. Lighter and faster than XML as on-the-wire data format Object Representation - Information is presented in object notations and hence better understandable. Easy to parse and conversion to objects for information consumption. Support multiple data types - JSON supports string, number, array, boolean whereas XML data are all string. | ||||
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Like Discuss Correct / Improve  json   markup language Asked in 1 Companies intermediate   frequent | ||||
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Ans. One can import the same package or same class multiple times. Neither compiler nor JVM complains wil complain about it. And the JVM will internally load the class only once no matter how many times you import the same class. | ||||
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Like Discuss Correct / Improve  java   import   jvm   advanced Asked in 1 Companies intermediate   rare | ||||
Frequently asked question for intermediate developers. Frequently asked in HCL Technologies and EPAM. | ||||
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Ans. Volatile is a declaration that a variable can be accessed by multiple threads and hence shouldnt be cached. | ||||
Sample Code for volatile | ||||
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Like Discuss Correct / Improve  java   oops   synchronization   volatile   java keywords Asked in 42 Companies intermediate   frequent | ||||
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Ans. It in Java is used to indicate that a field should not be serialized. | ||||
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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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Ans. No. Static methods belong to the class and not the objects. They belong to the class and hence doesn't fit properly for the polymorphic behavior. A static method is not associated with any instance of a class so the concept of overriding for runtime polymorphism using static methods is not applicable. | ||||
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Very frequently asked in phone and walk in interviews. | ||||
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Ans. An interface without any method declaration is called as marker interface. there are 3 in-built interfaces in JVM i.e. serializable, clonable, remote | ||||
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Ans. Class , Heap , Stack , Register , Native Method Stack. | ||||
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Ans. Pointers are vulnerable and slight carelessness in their use may result in memory problems and hence Java intrinsically manage their use. | ||||
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Ans. No, because both this and super should be the first statement. | ||||
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Ans. No Abstract methods can only be declared protected or public. | ||||
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Ans. System.console() returns null if your application is not run in a terminal (though you can handle this in your application)System.console() provides methods for reading password without echoing charactersSystem.out and System.err use the default platform encoding, while the Console class output methods use the console encoding | ||||
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Ans. As we only downcast class in the hierarchy, The ClassCastException is thrown to indicate that code has attempted to cast an object to a subclass of which it is not an instance. | ||||
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Usually asked only to fresh graduates and less experienced developers. | ||||
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Ans. These are threads that normally run at a low priority and provide a basic service to a program or programs when activity on a machine is reduced. garbage collector thread is daemon thread. | ||||
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Ans. No. Every Class only needs to have one constructor - With parameters or without parameters. Compiler provides a default non parameterized constructor if no constructors is defined. | ||||
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Ans. No. Even though "this" would mean a reference to current object id the method gets called using object reference but "this" would mean an ambiguity if the same static method gets called using Class name. | ||||
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Ans. It is used to sort collections and arrays of objects using the collections.sort() and java.utils. The objects of the class implementing the Comparable interface can be ordered. | ||||
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Ans. The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region | ||||
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Ans. Externalizable is an interface which contains two methods readExternal and writeExternal. These methods give you a control over the serialization mechanism. | ||||
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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. Collection should have an index for random access. 2. Collection should have ordered elements. | ||||
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Ans. PATH is the variable that holds the directories for the OS to look for executables. CLASSPATH is the variable that holds the directories for JVM to look for .class files ( Byte Code ). | ||||
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Like Discuss Correct / Improve  java   path   classpath   byte code   jvm   basic interview question Asked in 3 Companies intermediate   rare | ||||
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Ans. true, due to String Pool, both will point to a same String object. | ||||
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Very frequently asked in companies using SOA. | ||||
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Ans. REST or Representational State Transfer is a flexible architecture style for creating web services that recommends the following guidelines - 1. http for client server communication, 2. XML / JSON as formatiing language , 3. Simple URI as address for the services and, 4. stateless communication. | ||||
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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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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. 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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Frequently asked question in companies using hibernate. | ||||
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Ans. 1. First level cache is enabled by default whereas Second level cache needs to be enabled explicitly. 2. First level Cache came with Hibernate 1.0 whereas Second level cache came with Hibernate 3.0. 3. First level Cache is Session specific whereas Second level cache is shared by sessions that is why First level cache is considered local and second level cache is considered global. | ||||
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Ans. no, It's like challenging the design of application. | ||||
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Ans. No. Compilation error. | ||||
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