What is the output of this program ? class main_arguments { public static void main(String [ ] args) { String [][] argument = new String[2][2]; int x; argument[0] = args; x = argument[0].length; for (int y = 0; y < x; y++) System.out.print(" " + argument[0][y]); } }

Correct Answer: Enumeration is twice as fast as compared to an Iterator and uses very less memory However, the Iterator is much safer compared to Enumeration, because other threads are not able to modify the collection object that is currently traversed by the iterator Also, Iteratorsallow the caller to remove elements from the underlying collection, something which is not possible with Enumerations

Correct Answer: The Big-O notation simply describes how well an algorithm scales or performs in the worst case scenario as the number of elements in a data structure increases The Big-O notation can also be used to describe other behavior such as memory consumption Since the collection classes are actually data structures, we usually use the Big-O notation to chose the best implementation to use, based on time, memory and performance Big-O notation can give a good indication about performance for large amounts of data

Correct Answer: Java Collections Framework provides a well designed set of interfaces and classes that support operations on a collections of objects The most basic interfaces that reside in the Java Collections Framework are: Collection, which represents a group of objects known as its elements Set, which is a collection that cannot contain duplicate elements List, which is an ordered collection and can contain duplicate elements Map, which is an object that maps keys to values and cannot contain duplicate keys

Correct Answer: - A process is an execution of a program, while a Thread is a single execution sequence within a process - A process can contain multiple threads A Thread is sometimes called a lightweight process

Correct Answer: There are three ways that can be used in order for a Thread to be created: A class may extend the Thread class A class may implement the Runnable interface An application can use the Executor framework, in order to create a thread pool The Runnable interface is preferred, as it does not require an object to inherit the Thread class In case your application design requires multiple inheritance, only interfaces can help you Also, the thread pool is very efficient and can be implemented and used very easily

Correct Answer: Autoboxing is the automatic conversion that the Java compiler makes between the primitive types and their corresponding object wrapper classes For example, converting an int to an Integer, a double to a Double, and so on If the conversion goes the other way, this is called unboxing

Correct Answer: A static variable in Java belongs to its class and its value remains the same for all its instances A static variable is initialized when the class is loaded by the JVM If your code tries to access a non-static variable, without any instance, the compiler will complain, because those variables are not created yet and they are not associated with any instance

Correct Answer: 1Main difference is methods of a Java interface are implicitly abstract and cannot have implementations A Java abstract class can have instance methods that implements a default behavior 2Variables declared in a Java interface is by default final An abstract class may contain non-final variables 3Members of a Java interface are public by default A Java abstract class can have the usual flavors of class members like private, protected, etc 4Java interface should be implemented using keyword ?implements?; A Java abstract class should be extended using keyword ?extends? 5An interface can extend another Java interface only, an abstract class can extend another Java class and implement multiple Java interfaces 6A Java class can implement multiple interfaces but it can extend only one abstract class 7Interface is absolutely abstract and cannot be instantiated; A Java abstract class also cannot be instantiated, but can be invoked if a main() exists 8In comparison with java abstract classes, java interfaces are slow as it requires extra indirection

Correct Answer: All are equal

Explanation:

All the statements are equal because inside an interface a variable declared will be public static final by default 

Correct Answer: During the time of declaration

Explanation:

They should be initialized during the time of declaration itself otherwise it is a compilation eror