Adv Java
Programming
JAVA Interview Questions and Answers Part 2
11. What is the difference between an Interface and an Abstract class?
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An abstract class can have instance methods that implement a default
behavior.
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An Interface can only declare constants and instance methods, but cannot
implement default behavior and all methods are implicitly abstract.
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An interface has all public members and no implementation.
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An abstract class is a class which may have the usual flavors of class
members (private, protected, etc.), but has some abstract methods.
12. What is the garbage collection in Java, and when is it used?
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The purpose of garbage collection is to identify and discard objects that
are no longer needed by a program so that their resources can be reclaimed and
reused.
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A Java object is subject to garbage collection when it becomes unreachable
to the program in which it is used.
13. Describe synchronization in respect to multithreading?
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With respect to multithreading, synchronization is the capability to
control the access of multiple threads to shared resources. Without synchonization,
it is possible for one thread to modify a shared variable while another thread
is in the process of using or updating same shared variable. This usually leads
to significant errors.
14. Explain different way of using thread?
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The thread could be implemented by using runnable interface or by inheriting
from the Thread class. The former is more advantageous, 'cause when you are
going for multiple inheritance..the only interface can help.
15. What are pass by reference and passby value?
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Pass By Reference means the passing the address itself rather than passing
the value. Passby Value means passing a copy of the value to be passed.
16. What is HashMap and Map?
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Map is Interface and Hashmap is class that implements that.
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Map: The features of Map interface are the elements should be stored
in key/value pairs. Map accepts null values also both as key and value. Map
does not accept duplicate keys (if added a duplicate, the earlier one is simply
overridden and not a compilation error or exception). These features are
inherited by HashMap.
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The Map and the derived classes of Map are part of
collections framework even though Map maintains its separate hierarchy. Map is
best suitable to store the properties of a student like name and marks or
telephone directory (name and telephone number). Map uses hashing algorithm to
return the value when a key is supplied.
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HashMap: is an implementation of Map. All the properties of Map,
discussed earlier, are attained by HashMap. To have the advantage of
performance, the HashMap object can be assigned explicitly with initial
capacity and load factor.
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The capacity gives the existing storage capability
and the load factor gives increment rate of providing additional capacity when
the existing capacity is exhausted.
17. Difference between HashMap and HashTable?
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The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized
and permits nulls. (HashMap allows null values as key and value whereas
Hashtable doesnt allow).
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HashMap does not guarantee that the order of the map will remain constant
over time.
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HashMap is unsynchronized and Hashtable is synchronized.
18. Difference between Vector and ArrayList?
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Vector is synchronized whereas arraylist is not.
19. Difference between Swing and Awt?
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AWT are heavy weight componenets. Swings are light weight components.Hence
swing works faster than AWT
20. What is the difference between a constructor and a method?
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A constructor is a member function of a class that is used to create
objects of that class. It has the same name as the class itself, has no return
type, and is invoked using the new operator.
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A method is an ordinary member function of a class. It has its own name, a
return type (which may be void), and is invoked using the dot operator.
