JAVA COLLECTIONS 1.1

11. What is the Collection interface?

The Collection interface provides support for the implementation of a mathematical bag - an unordered collection of objects that may contain duplicates.
           
12. What is the Set interface?

The Set interface provides methods for accessing the elements of a finite mathematical set. Sets do not allow duplicate elements.
           
13. What is the typical use of Hashtable?

Whenever a program wants to store a key value pair, one can use Hashtable.           

14. I am trying to store an object using a key in a Hashtable. And some other object already exists in that location, then what will happen? The existing object will be overwritten? Or the new object will be stored elsewhere?

The existing object will be overwritten and thus it will be lost.
           
15. What is the difference between the size and capacity of a Vector?

The size is the number of elements actually stored in the vector, while capacity is the maximum number of elements it can store at a given instance of time.
           
16. Can a vector contain heterogenous objects?

Yes a Vector can contain heterogenous objects. Because a Vector stores everything in terms of Object.
           
17. Can a ArrayList contain heterogenous objects?

Yes a ArrayList can contain heterogenous objects. Because a ArrayList stores everything in terms of Object.
           
18. What is an enumeration?

An enumeration is an interface containing methods for accessing the underlying data structure from which the enumeration is obtained. It is a construct which collection classes return when you request a collection of all the objects stored in the collection. It allows sequential access to all the elements stored in the collection.
           
19. Considering the basic properties of Vector and ArrayList, where will you use Vector and where will you use ArrayList?

The basic difference between a Vector and an ArrayList is that, vector is synchronized while ArrayList is not. Thus whenever there is a possibility of multiple threads accessing the same instance, one should use Vector. While if not multiple threads are going to access the same instance then use ArrayList. Non synchronized data structure will give better performance than the synchronized one.
           
20. Can a vector contain heterogenous objects?

Yes a Vector can contain heterogenous objects. Because a Vector stores everything in terms of Object.

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JAVA COLLECTIONS 1.0

1. What is the Collections API?

The Collections API is a set of classes and interfaces that support operations on collections of objects.
           
2. What is the List interface?

The List interface provides support for ordered collections of objects.
           
3. What is the Vector class?

The Vector class provides the capability to implement a growable array of objects.
           
4. What is an Iterator interface?

The Iterator interface is used to step through the elements of a Collection .
           
5. Which java.util classes and interfaces support event handling?

The EventObject class and the EventListener interface support event processing.
           
6. What is the GregorianCalendar class?

The GregorianCalendar provides support for traditional Western calendars
           
7. What is the Locale class?

The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region.
           
8. What is the SimpleTimeZone class?

The SimpleTimeZone class provides support for a Gregorian calendar .
           
9. What is the Map interface?

The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with values.
           
10. What is the highest-level event class of the event-delegation model?

The java.util.EventObject class is the highest-level class in the event-delegation class hierarchy.

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HCL & HP Java/J2EE Technical question Set 1.0

1. What is the difference between an Interface and an Abstract class?

An abstract class can have instance methods that implement a default behavior. An Interface can only declare constants and instance methods, but cannot implement default behavior and all methods are implicitly abstract. An interface has all public members and no implementation. An abstract class is a class which may have the usual flavors of class members (private, protected, etc.), but has some abstract methods.

2. What is the purpose of garbage collection in Java, and when is it used?

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. A Java object is subject to garbage collection when it becomes unreachable to the program in which it is used.
           
3. Describe synchronization in respect to multithreading.

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.
           
4. Explain different way of using thread?

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.
           
5. What are pass by reference and passby value?

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.

6. What is HashMap and Map?

Map is Interface and Hashmap is class that implements that.
           
7. Difference between HashMap and HashTable?

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). HashMap does not guarantee that the order of the map will remain constant over time. HashMap is unsynchronized and Hashtable is synchronized.
           
8. Difference between Vector and ArrayList?

Vector is synchronized whereas arraylist is not.

9. Difference between Swing and Awt?

AWT are heavy-weight componenets. Swings are light-weight components. Hence swing works faster than AWT.
           
10. What is the difference between a constructor and a method?

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.
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.

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