Java Interview Question & Answer Set-6

Q:	Is next a keyword in Java?
A:	No, next is not a keyword.

Q:	Is delete a keyword in Java?
A:	No, delete is not a keyword in Java. Java does not make use of explicit destructors the way C++ does.

Q:	Is exit a keyword in Java?
A:	No. To exit a program explicitly you use exit method in System object.

Q:	What happens if you dont initialize an instance variable of any of the primitive types in Java?
A:	Java by default initializes it to the default value for that primitive type. Thus an int will be initialized to 0, a boolean will be initialized to false.

Q:	What will be the initial value of an object reference which is defined as an instance variable?
A:	The object references are all initialized to null in Java. However in order to do anything useful with these references, you must set them to a valid object, else you will get NullPointerExceptions everywhere you try to use such default initialized references.

Q:	What are the different scopes for Java variables?
A:	The scope of a Java variable is determined by the context in which the variable is declared. Thus a java variable can have one of the three scopes at any given point in time. 1. Instance : - These are typical object level variables, they are initialized to default values at the time of creation of object, and remain accessible as long as the object accessible. 2. Local : - These are the variables that are defined within a method. They remain accessbile only during the course of method excecution. When the method finishes execution, these variables fall out of scope. 3. Static: - These are the class level variables. They are initialized when the class is loaded in JVM for the first time and remain there as long as the class remains loaded. They are not tied to any particular object instance.
Q:	What is the default value of the local variables?
A:	The local variables are not initialized to any default value, neither primitives nor object references. If you try to use these variables without initializing them explicitly, the java compiler will not compile the code. It will complain abt the local varaible not being initilized..

Q:	How many objects are created in the following piece of code? MyClass c1, c2, c3; c1 = new MyClass (); c3 = new MyClass ();
A:	Only 2 objects are created, c1 and c3. The reference c2 is only declared and not initialized.

Q:	Can a public class MyClass be defined in a source file named YourClass.java?
A:	No the source file name, if it contains a public class, must be the same as the public class name itself with a .java extension.

Q:	Can main method be declared final?
A:	Yes, the main method can be declared final, in addition to being public static.

Q:	What will be the output of the following statement?System.out.println ("1" + 3);
A:	It will print 13.

Q:	What will be the default values of all the elements of an array defined as an instance variable?
A:	If the array is an array of primitive types, then all the elements of the array will be initialized to the default value corresponding to that primitive type. e.g. All the elements of an array of int will be initialized to 0, while that of boolean type will be initialized to false. Whereas if the array is an array of references (of any type), all the elements will be initialized to null.

Q:	What is the Collections API?
A:	The Collections API is a set of classes and interfaces that support operations on collections of objects.

Q:	What is the List interface?
A:	The List interface provides support for ordered collections of objects.

Q:	What is the Vector class?
A:	The Vector class provides the capability to implement a growable array of objects.

Q:	What is an Iterator interface?
A:	The Iterator interface is used to step through the elements of a Collection .

Q:	Which java.util classes and interfaces support event handling?
A:	The EventObject class and the EventListener interface support event processing.

Q:	What is the GregorianCalendar class?
A:	The GregorianCalendar provides support for traditional Western calendars

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

Q:	What is the SimpleTimeZone class?
A:	The SimpleTimeZone class provides support for a Gregorian calendar .

Q:	What is the Map interface?
A:	The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with values.

Q:	What is the highest-level event class of the event-delegation model?
A:	The java.util.EventObject class is the highest-level class in the event-delegation class hierarchy.

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

Q:	What is the Set interface?
A:	The Set interface provides methods for accessing the elements of a finite mathematical set. Sets do not allow duplicate elements.

Q:	What is the typical use of Hashtable?
A:	Whenever a program wants to store a key value pair, one can use Hashtable.

Q:	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?
A:	The existing object will be overwritten and thus it will be lost.

Q:	What is the difference between the size and capacity of a Vector?
A:	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.

Q:	Can a vector contain heterogenous objects?
A:	Yes a Vector can contain heterogenous objects. Because a Vector stores everything in terms of Object.

Q:	Can a ArrayList contain heterogenous objects?
A:	Yes a ArrayList can contain heterogenous objects. Because a ArrayList stores everything in terms of Object.

Q:	What is an enumeration?
A:	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.

Q:	Considering the basic properties of Vector and ArrayList, where will you use Vector and where will you use ArrayList?
A:	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.

Q:	Can a vector contain heterogenous objects?
A:	Yes a Vector can contain heterogenous objects. Because a Vector stores everything in terms of Object.