Question 1

What is difference between Path and Classpath?

Accepted Answer

PATH and CLASSPATH are operating system level environment variables PATH is used to define where the system can find the executables (exe) files whereas CLASSPATH is used to specify the location of class files

Question 2

Is Java a pure object oriented language?

Accepted Answer

Java uses primitive data types and hence is not a pure object oriented language

Question 3

How to define a constant variable in Java?

Accepted Answer

The variable should be declared as static and final So only one copy of the variable exists for all instances of the class and the value can't be changed also static final int PI = 214; is an example for constant

Question 4

What is the access scope of a protected method?

Accepted Answer

A protected method can be accessed by the classes within the same package or by the subclasses of the class in any package

Question 5

What is the impact of declaring a method as final?

Accepted Answer

A method declared as final can't be overridden A sub-class can't have the same method signature with a different implementation

Question 6

Which of the following is not used for commenting in java?

Accepted Answer

// is a single line comment /* */ is commenting on one or more lines /** */ is documentation comment

Question 7

Which is true?

Accepted Answer

A is incorrect because classes implement interfaces, they don't extend them. B is incorrect because interfaces only "inherit from" other interfaces. D is incorrect based on the preceding rules.

Question 8

class Hell { public static void main(String[] args) { Integer i = 42; String s = (i<40)?"life":(i>50)?"base":"ball"; System.out.println(s); } }

Accepted Answer

D is correct. This is a ternary nested in a ternary with a little unboxing thrown in.Both of the ternary expressions are false.

Question 9

try { int x = Integer.parseInt("two"); } Which could be used to create an appropriate catch block?

Accepted Answer

C is correct. 'Integer.parseInt' can throw a NumberFormatException, and IllegalArgumentException is its superclass

Question 10

Difference between Java Beans & Servlets?

Accepted Answer

java bean is a reusable component, where as the servlet is the java program which extends the server capability

Question 11

Just by seeing the signature of the bean how can you specity whether it is a Statefull of Stateless Session Bean?

Accepted Answer

The create method in a stateless bean cannot have arguments, and can only have a single method called create() While create in Stateful bean can have arguments and could be any method starting with create string eg create(arg1, arg2, ) Although it is not compiler checked but in stateless bean the ejb Passivate() and ejb Active() methods has to be empty as these functions are never called by EJB container As conceptually in stateful session bean we might need to store the clients information hence arguments in createare necessary While in stateless bean we don't hence no arguments are necessary It's intutive isn't intutive isn't I my life I haven't seen such a futuristic server programming tool as EJB

Question 12

How are this() and super() used with constructors?

Accepted Answer

Constructors use this to refer to another constructor in the same class with a different parameter list Constructors use super to invoke the superclass's constructor If a constructor uses super, it must use it in the first line; otherwise, the compiler will complain

Question 13

How do you decide when to use HashMap and when to use TreeMap ?

Accepted Answer

For inserting, deleting, and locating elements in a Map, the HashMap offers the best alternative If, however, you need to traverse the keys in a sorted order, then TreeMap is your better alternative Depending upon the size of your collection, it may be faster to add elements to a HashMap, then convert the map to a TreeMap for sorted key traversal

Question 14

What is the Dictionary class?

Accepted Answer

- The Dictionary class is an abstract class - Classes like Hashtable which map keys to values inherit from this class - An object can be looked for if a dictionary and a key is provided - Any non-null object can be used as a key and as a value

Question 15

What is the common usage of serialization? What exceptions occur during serialization?

Accepted Answer

The object need to be serialized when it’s sent over a network and when it’s state is saved Exceptions which occur during serialization are: a transient fields b when the base class is serialized then only base class fields are handled c static fields are ignored because they are not part of any state

Question 16

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

Accepted Answer

The purpose of garbage collection is to identify and discard those objects that are no longer needed by the application, in order for the resources to be reclaimed and reused

Question 17

When is the finalize() called ? What is the purpose of finalization ?

Accepted Answer

The finalize method is called by the garbage collector, just before releasing the object’s memory It is normally advised to release resources held by the object inside the finalize method

Question 18

What is Marker Interface?

Accepted Answer

An interface without having any methods and by implementing that interface if our objects will get same ability such type interfaces are called marker interface (or) ability interface (or) tag interface

Question 19

X implements Y extends Z

Accepted Answer

It is a compilation error it should be X extends Y implements Z

Question 20

Which of the following are valied?

Accepted Answer

A is wrong because a class can extend nly one class .B is wrong because a class can implement any number of interfaces.C is wronb because both can can be done simulteneously.So, D is correct

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