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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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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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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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Q72. What is the difference between System.console.write and System.out.println ?
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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Which of the following can throw ClassCastException ?
UpCasting
DownCasting
Casting to incompatible data type
Casting to Strings
x instanceOf y returns false ..
if x is an instance of y class
if x is an instance of class implementing y interface
if x is an instance of class extending y class
if x is an instance of Class which is a parent of Y class
Usually asked only to fresh graduates and less experienced developers.
Q74. What is a daemon thread? Give an Example ?
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. 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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Q80. Difference between new operator and Class.forName().newInstance() ?
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. 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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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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Which of the following collection maintain its elements in Natural Sorted order ?
HashMap
TreeMap
LinkedHashMap
LinkedMap
Which method needs to be implemented if a class is implementing comparable interface ?
comp
compare
compareTo
compareEquals
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.
Q86. What is rule regarding overriding equals and hashCode method ?
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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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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json markup language 
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Frequently asked question for intermediate developers. Frequently asked in HCL Technologies and EPAM.
Sample Code for volatile
Which of the following is not an advantage of JSON over XML ?
