Collected & Edited By:
Gururaj.B.Kulkarni
guruk2k5@gmail.com
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
My Words
Searching a job or changing a job is not an easy task. Especially for a fresher, it is difficult
to clear the interview procedure. Computer Science graduates or graduates from other branch,
who try to get into IT field, are bit lucky. The internet helps them to seek the help from blogs,
websites, discussion forums and other resources. But, internet doesn’t helps to seek the desired
solutions easily. One should know how to Google effectively since googling is also an art. I came
across so many resources to find questions and answers, asked in interviews often. I collected some
of the questions and answers from huge resource. When I looked back at my buddies, I felt that
couple of them are also struggling in the same way as me. So resource is to share with others, else it
will be only source. I feel it is a cup of coffee from coffee shop. I am able to fetch a cup of coffee for
you not the entire coffee available at coffee shop. If you feel this document is helpful, please forward
to others. If you find any wrong or misleading information in the document, you can mail me at
guruk2k5@gmail.com with a description note. This document deals with only java related question.
Reader’s support encourages to produce the same kind of a document for other concepts like,
.NET, FLEX, PHP,PERL, C, C++, Database, Operating systems etc. Here I acknowledge my
gratitude to all my friends who are my backbones.
Thank you.
Gururaj.B.Kulkarni
guruk2k5@gmail.com
http://myblog-gururaj.blogspot.com
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
CORE JAVA
Q. Explain the Public ,Private and Protected access modifiers?
a)public: public can be accessed from anywhere.
b)private:private can’t be seen outside of its class.
c)protected:protected can be accessed by classes in the same package and subclasses in the other
packages.
Q. Explain the final Keyword?
a)Final keyword can be applied to class, method and variables.
b)Final class can not be inherited.
c)Final method can not be overridden.
d)Final variable can not be changed after initialisation.
Q. Explain the Finalize() method?
finalize() method is used just before an object is destroyed and can be called just prior to garbage
collection.
Q. What is UNICODE?
UNICODE is an international standard for represanting characters.It uses two byte to represent a
character.
Q. What is the difference between Volatile and Transient Modifiers?
a)Volatile: Volatile modifier tells the compiler that the variable can be changed unexpectedly by other
parts of the program.
b)Transient: Transient modifier tells the compiler that the variable can not be serialized.
Q. What is the difference between Overloading and overriding?
a)overloading: different methods share the same name in the same class.overloading must have
different signature for methods.
b)overriding:childclass method replaces the parentclass method.overriding must have same signature
for methods.
Q. What is a package?
A package is a collection of classes and interfaces which provides access protection and name space
management.
Q: What is the difference between an Interface and an Abstract class?
A: 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
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
is a class which may have the usual flavors of class members (private, protected, etc.), but has some
abstract methods.
Q: What is the purpose of garbage collection in Java, and when is it used?
A: 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.
Q: Describe synchronization in respect to multithreading.
A: 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.
Q: Explain different way of using thread?
A: 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.
Q: What are pass by reference and passby value?
A: 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.
Q: What is HashMap and Map?
A: Map is Interface and Hashmap is class that implements that.
Q: Difference between HashMap and HashTable?
A: 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.
Q: Difference between Vector and ArrayList?
A: Vector is synchronized whereas arraylist is not.
Q: Difference between Swing and Awt?
A: AWT are heavy-weight componenets. Swings are light-weight components. Hence swing works
faster than AWT.
Q: What is the difference between a constructor and a method?
A: 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.
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
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.
Q: What is an Iterator?
A: Some of the collection classes provide traversal of their contents via a java.util.Iterator interface.
This interface allows you to walk through a collection of objects, operating on each object in turn.
Remember when using Iterators that they contain a snapshot of the collection at the time the Iterator
was obtained; generally it is not advisable to modify the collection itself while traversing an Iterator.
Q: State the significance of public, private, protected, default modifiers both singly and in
combination and state the effect of package relationships on declared items qualified by these
modifiers.
A: public : Public class is visible in other packages, field is visible everywhere (class must be public too)
private : Private variables or methods may be used only by an instance of the same class that declares
the variable or method, A private feature may only be accessed by the class that owns the feature.
protected : Is available to all classes in the same package and also available to all subclasses of the
class that owns the protected feature.This access is provided even to subclasses that reside in a
different package from the class that owns the protected feature.
default :What you get by default ie, without any access modifier (ie, public private or protected).It
means that it is visible to all within a particular package.
Q: What is an abstract class?
A: Abstract class must be extended/subclassed (to be useful). It serves as a template. A class that is
abstract may not be instantiated (ie, you may not call its constructor), abstract class may contain
static data. Any class with an abstract method is automatically abstract itself, and must be declared as
such.
A class may be declared abstract even if it has no abstract methods. This prevents it from being
instantiated.
Q: What is static in java?
A: Static means one per class, not one for each object no matter how many instance of a class might
exist. This means that you can use them without creating an instance of a class.Static methods are
implicitly final, because overriding is done based on the type of the object, and static methods are
attached to a class, not an object. A static method in a superclass can be shadowed by another static
method in a subclass, as long as the original method was not declared final. However, you can't
override a static method with a nonstatic method. In other words, you can't change a static method
into an instance method in a subclass.
Q: What is final?
A: A final class can't be extended ie., final class may not be subclassed. A final method can't be
overridden when its class is inherited. You can't change value of a final variable (is a constant).
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
Q: What if the main method is declared as private?
A: The program compiles properly but at runtime it will give "Main method not public." message.
Q: What if the static modifier is removed from the signature of the main method?
A: Program compiles. But at runtime throws an error "NoSuchMethodError".
Q: What if I write static public void instead of public static void?
A: Program compiles and runs properly.
Q: What if I do not provide the String array as the argument to the method?
A: Program compiles but throws a runtime error "NoSuchMethodError".
Q: What is the first argument of the String array in main method?
A: The String array is empty. It does not have any element. This is unlike C/C++ where the first
element by default is the program name.
Q: If I do not provide any arguments on the command line, then the String array of Main method will
be empty or null?
A: It is empty. But not null.
Q: How can one prove that the array is not null but empty using one line of code?
A: Print args.length. It will print 0. That means it is empty. But if it would have been null then it would
have thrown a NullPointerException on attempting to print args.length.
Q: What environment variables do I need to set on my machine in order to be able to run Java
programs?
A: CLASSPATH and PATH are the two variables.
Q: Can an application have multiple classes having main method?
A: Yes it is possible. While starting the application we mention the class name to be run. The JVM will
look for the Main method only in the class whose name you have mentioned. Hence there is not
conflict amongst the multiple classes having main method.
Q: Can I have multiple main methods in the same class?
A: No the program fails to compile. The compiler says that the main method is already defined in the
class.
Q: Do I need to import java.lang package any time? Why ?
A: No. It is by default loaded internally by the JVM.
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
Q: Can I import same package/class twice? Will the JVM load the package twice at runtime?
A: One can import the same package or same class multiple times. Neither compiler nor JVM
complains abt it. And the JVM will internally load the class only once no matter how many times you
import the same class.
Q: What are Checked and UnChecked Exception?
A: A checked exception is some subclass of Exception (or Exception itself), excluding class
RuntimeException and its subclasses.
Making an exception checked forces client programmers to deal with the possibility that the
exception will be thrown. eg, IOException thrown by java.io.FileInputStream's read() method•
Unchecked exceptions are RuntimeException and any of its subclasses. Class Error and its subclasses
also are unchecked. With an unchecked exception, however, the compiler doesn't force client
programmers either to catch the
exception or declare it in a throws clause. In fact, client programmers may not even know that the
exception could be thrown. eg, StringIndexOutOfBoundsException thrown by String's charAt()
method• Checked exceptions must be caught at compile time. Runtime exceptions do not need to be.
Errors often cannot be.
Q: What is Overriding?
A: When a class defines a method using the same name, return type, and arguments as a method in its
superclass, the method in the class overrides the method in the superclass.
When the method is invoked for an object of the class, it is the new definition of the method that is
called, and not the method definition from superclass. Methods may be overridden to be more public,
not more private.
Q: What are different types of inner classes?
A: Nested top-level classes, Member classes, Local classes, Anonymous classesNested top-level
classes- If you declare a class within a class and specify the static modifier, the compiler treats the
class just like any other top-level class.
Any class outside the declaring class accesses the nested class with the declaring class name acting
similarly to a package. eg, outer.inner. Top-level inner classes implicitly have access only to static
variables.There can also be inner interfaces. All of these are of the nested top-level variety.
Member classes - Member inner classes are just like other member methods and member variables
and access to the member class is restricted, just like methods and variables. This means a public
member class acts similarly to a nested top-level class. The primary difference between member
classes and nested top-level classes is that member classes have access to the specific instance of the
enclosing class.
Local classes - Local classes are like local variables, specific to a block of code. Their visibility is only
within the block of their declaration. In order for the class to be useful beyond the declaration block,
it would need to implement a
more publicly available interface.Because local classes are not members, the modifiers public,
protected, private, and static are not usable.
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
Anonymous classes - Anonymous inner classes extend local inner classes one level further. As
anonymous classes have no name, you cannot provide a constructor.
Q: Are the imports checked for validity at compile time? e.g. will the code containing an import such
as java.lang.ABCD compile?
A: Yes. the imports are checked for the semantic validity at compile time. The code containing above
line of import will not compile. It will throw an error saying,can not resolve symbol
symbol : class ABCD
location: package io
import java.io.ABCD;
Q: Does importing a package imports the subpackages as well? e.g. Does importing com.MyTest.* also
import com.MyTest.UnitTests.*?
A: No. you will have to import the subpackages explicitly. Importing com.MyTest.* will import classes
in the package MyTest only. It will not import any class in any of it's subpackage.
Q: What is the difference between declaring a variable and defining a variable?
A: In declaration we just mention the type of the variable and it's name. We do not initialize it. But
defining means declaration + initialization.
e.g String s; is just a declaration while String s = new String ("abcd"); Or String s = "abcd"; are both
definitions.
Q: What is the default value of an object reference declared as an instance variable?
A: null unless we define it explicitly.
Q: Can a top level class be private or protected?
A: No. A top level class can not be private or protected. It can have either "public" or no modifier. If it
does not have a modifier it is supposed to have a default access.If a top level class is declared as
private the compiler will complain that the "modifier private is not allowed here". This means that a
top level class can not be private. Same is the case with protected.
Q: What type of parameter passing does Java support?
A: In Java the arguments are always passed by value .
Q: Primitive data types are passed by reference or pass by value?
A: Primitive data types are passed by value.
Q: Objects are passed by value or by reference?
A: Java only supports pass by value. With objects, the object reference itself is passed by value and so
both the original reference and parameter copy both refer to the same object .
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
Q: What is serialization?
A: Serialization is a mechanism by which you can save the state of an object by converting it to a byte
stream.
Q: How do I serialize an object to a file?
A: The class whose instances are to be serialized should implement an interface Serializable. Then you
pass the instance to the ObjectOutputStream which is connected to a fileoutputstream. This will save
the object to a file.
Q: Which methods of Serializable interface should I implement?
A: The serializable interface is an empty interface, it does not contain any methods. So we do not
implement any methods.
Q: How can I customize the seralization process? i.e. how can one have a control over the serialization
process?
A: Yes it is possible to have control over serialization process. The class should implement
Externalizable interface. This interface contains two methods namely readExternal and writeExternal.
You should implement these methods and write the logic for customizing the serialization process.
Q: What is the common usage of serialization?
A: Whenever an object is to be sent over the network, objects need to be serialized. Moreover if the
state of an object is to be saved, objects need to be serilazed.
Q: What is Externalizable interface?
A: Externalizable is an interface which contains two methods readExternal and writeExternal. These
methods give you a control over the serialization mechanism. Thus if your class implements this
interface, you can customize the serialization process by implementing these methods.
Q: When you serialize an object, what happens to the object references included in the object?
A: The serialization mechanism generates an object graph for serialization. Thus it determines
whether the included object references are serializable or not. This is a recursive process. Thus when
an object is serialized, all the included objects are also serialized alongwith the original object.
Q: What one should take care of while serializing the object?
A: One should make sure that all the included objects are also serializable. If any of the objects is not
serializable then it throws a NotSerializableException.
Q: What happens to the static fields of a class during serialization?
A: There are three exceptions in which serialization doesnot necessarily read and write to the stream.
These are
1. Serialization ignores static fields, because they are not part of ay particular state state.
2. Base class fields are only hendled if the base class itself is serializable.
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
3. Transient fields.
Q: Does Java provide any construct to find out the size of an object?
A:No there is not sizeof operator in Java. So there is not direct way to determine the size of an object
directly in Java.
Q: Give a simplest way to find out the time a method takes for execution without using any profiling
tool?
A:Read the system time just before the method is invoked and immediately after method returns.
Take the time difference, which will give you the time taken by a method for execution.
To put it in code...
long start = System.currentTimeMillis ();
method ();
long end = System.currentTimeMillis ();
System.out.println ("Time taken for execution is " + (end - start));
Remember that if the time taken for execution is too small, it might show that it is taking zero
milliseconds for execution. Try it on a method which is big enough, in the sense the one which is doing
considerable amount of processing.
Q: What are wrapper classes?
A:Java provides specialized classes corresponding to each of the primitive data types. These are called
wrapper classes. They are e.g. Integer, Character, Double etc.
Q: Why do we need wrapper classes?
A: It is sometimes easier to deal with primitives as objects. Moreover most of the collection classes
store objects and not primitive data types. And also the wrapper classes provide many utility methods
also. Because of these resons we need wrapper classes. And since we create instances of these classes
we can store them in any of the collection classes and pass them around as a collection. Also we can
pass them around as method parameters where a method expects an object.
Q: What are checked exceptions?
A: Checked exception are those which the Java compiler forces you to catch. e.g. IOException are
checked Exceptions.
Q: What are runtime exceptions?
A: Runtime exceptions are those exceptions that are thrown at runtime because of either wrong input
data or because of wrong business logic etc. These are not checked by the compiler at compile time.
Q: What is the difference between error and an exception?
A: An error is an irrecoverable condition occurring at runtime. Such as OutOfMemory error. These
JVM errors and you can not repair them at runtime. While exceptions are conditions that occur
because of bad input etc. e.g. FileNotFoundException will be thrown if the specified file does not exist.
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
Or a NullPointerException will take place if you try using a null reference. In most of the cases it is
possible to recover from an exception (probably by giving user a feedback for entering proper values
etc.).
Q: How to create custom exceptions?
A: Your class should extend class Exception, or some more specific type thereof.
Q: If I want an object of my class to be thrown as an exception object, what should I do?
A: The class should extend from Exception class. Or you can extend your class from some more precise
exception type also.
Q: If my class already extends from some other class what should I do if I want an instance of my class
to be thrown as an exception object?
A: One can not do anytihng in this scenarion. Because Java does not allow multiple inheritance and
does not provide any exception interface as well.
Q: How does an exception permeate through the code?
A: An unhandled exception moves up the method stack in search of a matching When an exception is
thrown from a code which is wrapped in a try block followed by one or more catch blocks, a search is
made for matching catch block. If a matching type is found then that block will be invoked. If a
matching type is not found then the exception moves up the method stack and reaches the caller
method. Same procedure is repeated if the caller method is included in a try catch block. This process
continues until a catch block handling the appropriate type of exception is found. If it does not find
such a block then finally the program terminates.
Q: What are the different ways to handle exceptions?
A: There are two ways to handle exceptions,
1. By wrapping the desired code in a try block followed by a catch block to catch the exceptions. and
2. List the desired exceptions in the throws clause of the method and let the caller of the method
hadle those exceptions.
Q: What is the basic difference between the 2 approaches to exception handling.
1> try catch block and
2> specifying the candidate exceptions in the throws clause?
When should you use which approach?
A: In the first approach as a programmer of the method, you urself are dealing with the exception.
This is fine if you are in a best position to decide should be done in case of an exception. Whereas if it
is not the responsibility of the method to deal with it's own exceptions, then do not use this approach.
In this case use the second approach. In the second approach we are forcing the caller of the method
to catch the exceptions, that the method is likely to throw. This is often the approach library creators
use. They list the exception in the throws clause and we must catch them. You will find the same
approach throughout the java libraries we use.
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
Q: Is it necessary that each try block must be followed by a catch block?
A: It is not necessary that each try block must be followed by a catch block. It should be followed by
either a catch block OR a finally block. And whatever exceptions are likely to be thrown should be
declared in the throws clause of the method.
Q: If I write return at the end of the try block, will the finally block still execute?
A: Yes even if you write return as the last statement in the try block and no exception occurs, the
finally block will execute. The finally block will execute and then the control return.
Q: If I write System.exit (0); at the end of the try block, will the finally block still execute?
A: No in this case the finally block will not execute because when you say System.exit (0); the control
immediately goes out of the program, and thus finally never executes.
Q: How are Observer and Observable used?
A: Objects that subclass the Observable class maintain a list of observers. When an Observable object
is updated it invokes the update() method of each of its observers to notify the observers that it has
changed state. The Observer interface is implemented by objects that observe Observable objects.
Q: What is synchronization and why is it important?
A: With respect to multithreading, synchronization is the capability to control
the access of multiple threads to shared resources. Without synchronization, it is possible for one
thread to modify a shared object while another thread is in the process of using or updating that
object's value. This often leads to significant errors.
Q: How does Java handle integer overflows and underflows?
A: It uses those low order bytes of the result that can fit into the size of the type allowed by the
operation.
Q: Does garbage collection guarantee that a program will not run out of memory?
A: Garbage collection does not guarantee that a program will not run out of memory. It is possible for
programs to use up memory resources faster than they are garbage collected. It is also possible for
programs to create objects that are not subject to garbage collection.
Q: What is the difference between preemptive scheduling and time slicing?
A: Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead
states or a higher priority task comes into existence. Under time slicing, a task executes for a
predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines
which task should execute next, based on priority and other factors.
Q: When a thread is created and started, what is its initial state?
A: A thread is in the ready state after it has been created and started.
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
Q: What is the purpose of finalization?
A: The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup
processing before the object is garbage collected.
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 difference between a while statement and a do statement?
A: A while statement checks at the beginning of a loop to see whether the next loop iteration should
occur. A do statement checks at the end of a loop to see whether the next iteration of a loop should
occur. The do statement will always execute the body of a loop at least once.
Q: What is the difference between static and non-static variables?
A: A static variable is associated with the class as a whole rather than with specific instances of a class.
Non-static variables take on unique values with each object instance.
Q: How are this() and super() used with constructors?
A: This() is used to invoke a constructor of the same class. super() is used to invoke a superclass
constructor.
Q: What are synchronized methods and synchronized statements?
A: Synchronized methods are methods that are used to control access to an object. A thread only
executes a synchronized method after it has acquired the lock for the method's object or class.
Synchronized statements are similar to synchronized methods. A synchronized statement can only be
executed after a thread has acquired the lock for the object or class referenced in the synchronized
statement.
Q: What is daemon thread and which method is used to create the daemon thread?
A: Daemon thread is a low priority thread which runs intermittently in the back ground doing the
garbage collection operation for the java runtime system. setDaemon method is used to create a
daemon thread.
Q: Can applets communicate with each other?
A: At this point in time applets may communicate with other applets running in the same virtual
machine. If the applets are of the same class, they can communicate via shared static variables. If the
applets are of different classes, then each will need a reference to the same class with static variables.
In any case the basic idea is to pass the information back and forth through a static variable.
An applet can also get references to all other applets on the same page using the getApplets()
method of java.applet.AppletContext. Once you get the reference to an applet, you can communicate
with it by using its public members.
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It is conceivable to have applets in different virtual machines that talk to a server somewhere
on the Internet and store any data that needs to be serialized there. Then, when another applet needs
this data, it could connect to this same server. Implementing this is non-trivial.
Q: What are the steps in the JDBC connection?
A: While making a JDBC connection we go through the following steps :
Step 1 : Register the database driver by using :
Class.forName(\" driver classs for that specific database\" );
Step 2 : Now create a database connection using :
Connection con = DriverManager.getConnection(url,username,password);
Step 3: Now Create a query using :
Statement stmt = Connection.Statement(\"select * from TABLE NAME\");
Step 4 : Exceute the query :
stmt.exceuteUpdate();
Q: How does a try statement determine which catch clause should be used to handle an exception?
A: When an exception is thrown within the body of a try statement, the catch clauses of the try
statement are examined in the order in which they appear. The first catch clause that is capable of
handling the exceptionis executed. The remaining catch clauses are ignored.
Q: Is Empty .java file a valid source file?
A: Yes, an empty .java file is a perfectly valid source file.
Q: Can a .java file contain more than one java classes?
A: Yes, a .java file contain more than one java classes, provided at the most one of them is a public
class.
Q: Is String a primitive data type in Java?
A: No String is not a primitive data type in Java, even though it is one of the most extensively used
object. Strings in Java are instances of String class defined in java.lang package.
Q: Is main a keyword in Java?
A: No, main is not a keyword in Java.
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.
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
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.
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
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.
Servlets, JSP,EJBs
Q: Explain the life cycle methods of a Servlet.
A: The javax.servlet.Servlet interface defines the three methods known as life-cycle method.
public void init(ServletConfig config) throws ServletException
public void service( ServletRequest req, ServletResponse res) throws ServletException, IOException
public void destroy()
First the servlet is constructed, then initialized wih the init() method.
Any request from client are handled initially by the service() method before delegating to the doXxx()
methods in the case of HttpServlet.
The servlet is removed from service, destroyed with the destroy() methid, then garbaged collected
and finalized.
Q: What is the difference between the getRequestDispatcher(String path) method of
javax.servlet.ServletRequest interface and javax.servlet.ServletContext interface?
A: The getRequestDispatcher(String path) method of javax.servlet.ServletRequest interface accepts
parameter the path to the resource to be included or forwarded to, which can be relative to the
request of the calling servlet. If the path begins with a "/" it is interpreted as relative to the current
context root.
The getRequestDispatcher(String path) method of javax.servlet.ServletContext interface
cannot accepts relative paths. All path must sart with a "/" and are interpreted as relative to curent
context root.
Q: Explain the directory structure of a web application.
A: The directory structure of a web application consists of two parts.
A private directory called WEB-INF
A public resource directory which contains public resource folder.
WEB-INF folder consists of
1. web.xml
2. classes directory
3. lib directory
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
Q: What are the common mechanisms used for session tracking?
A: Cookies
SSL sessions
URL- rewriting
Q: Explain ServletContext.
A: ServletContext interface is a window for a servlet to view it's environment. A servlet can use this
interface to get information such as initialization parameters for the web applicationor servlet
container's version. Every web application has one and only one ServletContext and is accessible to all
active resource of that application.
Q: What is preinitialization of a servlet?
A: A container doesnot initialize the servlets ass soon as it starts up, it initializes a servlet when it
receives a request for that servlet first time. This is called lazy loading. The servlet specification
defines the
the servlet container load and initialize the servlet as soon as it starts up. The process of loading a
servlet before any request comes in is called preloading or preinitializing a servlet.
Q: What is the difference between Difference between doGet() and doPost()?
A: A doGet() method is limited with 2k of data to be sent, and doPost() method doesn't have this
limitation. A request string for doGet() looks like the following:
http://www.allapplabs.com/svt1?p1=v1&p2=v2&...&pN=vN
doPost() method call doesn't need a long text tail after a servlet name in a request. All parameters are
stored in a request itself, not in a request string, and it's impossible to guess the data transmitted to a
servlet only looking at a request string.
Q: What is the difference between HttpServlet and GenericServlet?
A: A GenericServlet has a service() method aimed to handle requests. HttpServlet extends
GenericServlet and adds support for doGet(), doPost(), doHead() methods (HTTP 1.0) plus doPut(),
doOptions(), doDelete(), doTrace() methods (HTTP 1.1).
Both these classes are abstract.
Q: What is the difference between ServletContext and ServletConfig?
A: ServletContext: Defines a set of methods that a servlet uses to communicate with its servlet
container, for example, to get the MIME type of a file, dispatch requests, or write to a log file.The
ServletContext object is contained within the ServletConfig object, which the Web server provides the
servlet when the servlet is initialized
ServletConfig: The object created after a servlet is instantiated and its default constructor is read. It is
created to pass initialization information to the servlet.
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
Q: What is a output comment?
A: A comment that is sent to the client in the viewable page source.The JSP engine handles an output
comment as uninterpreted HTML text, returning the comment in the HTML output sent to the client.
You can see the comment by viewing the page source from your Web browser.
JSP Syntax
Example 1
Displays in the page source:
Q: What is a Hidden Comment?
A: A comments that documents the JSP page but is not sent to the client. The JSP engine ignores a
hidden comment, and does not process any code within hidden comment tags. A hidden comment is
not sent to the client, either in the displayed JSP page or the HTML page source. The hidden comment
is useful when you want to hide or "comment out" part of your JSP page.
You can use any characters in the body of the comment except the closing --%> combination. If you
need to use --%> in your comment, you can escape it by typing --%\>.
JSP Syntax
<%-- comment --%>
Examples
<%@ page language="java" %>
<%-- This comment will not be visible to the colent in the page source --%>
Q: What is a Expression?
A: An expression tag contains a scripting language expression that is evaluated, converted to a String,
and inserted where the expression appears in the JSP file. Because the value of an expression is
converted to a String, you can use an expression within text in a JSP file. Like
<%= someexpression %>
<%= (new java.util.Date()).toLocaleString() %>
You cannot use a semicolon to end an expression
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
Q: What is a Declaration?
A: A declaration declares one or more variables or methods for use later in the JSP source file.
A declaration must contain at least one complete declarative statement. You can declare any number
of variables or methods within one declaration tag, as long as they are separated by semicolons. The
declaration must be valid in the scripting language used in the JSP file.
<%! somedeclarations %>
<%! int i = 0; %>
<%! int a, b, c; %>
Q: What is a Scriptlet?
A: A scriptlet can contain any number of language statements, variable or method declarations, or
expressions that are valid in the page scripting language.Within scriptlet tags, you can
1.Declare variables or methods to use later in the file (see also Declaration).
2.Write expressions valid in the page scripting language (see also Expression).
3.Use any of the JSP implicit objects or any object declared with a
You must write plain text, HTML-encoded text, or other JSP tags outside the scriptlet.
Scriptlets are executed at request time, when the JSP engine processes the client request. If the
scriptlet produces output, the output is stored in the out object, from which you can display it.
Q: What are implicit objects? List them?
A: Certain objects that are available for the use in JSP documents without being declared first. These
objects are parsed by the JSP engine and inserted into the generated servlet. The implicit objects re
listed below
•request
•response
•pageContext
•session
•application
•out
•config
•page
•exception
Q: Difference between forward and sendRedirect?
A: When you invoke a forward request, the request is sent to another resource on the server, without
the client being informed that a different resource is going to process the request. This process occurs
completely within the web container. When a sendRedirtect method is invoked, it causes the web
container to return to the browser indicating that a new URL should be requested. Because the
browser issues a completely new request any object that are stored as request attributes before the
redirect occurs will be lost. This extra round trip a redirect is slower than forward.
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
Q: What are the different scope values for the
A: The different scope values for
1. page
2. request
3.session
4.application
Q: Explain the life-cycle mehtods in JSP?
A: THe generated servlet class for a JSP page implements the HttpJspPage interface of the
javax.servlet.jsp package. Hte HttpJspPage interface extends the JspPage interface which inturn
extends the Servlet interface of the javax.servlet package. the generated servlet class thus
implements all the methods of the these three interfaces. The JspPage interface declares only two
mehtods - jspInit() and jspDestroy() that must be implemented by all JSP pages regardless of the
client-server protocol. However the JSP specification has provided the HttpJspPage interfaec
specifically for the JSp pages serving HTTP requests. This interface declares one method _jspService().
The jspInit()- The container calls the jspInit() to initialize te servlet instance.It is called before any
other method, and is called only once for a servlet instance.
The _jspservice()- The container calls the _jspservice() for each request, passing it the request and the
response objects.
The jspDestroy()- The container calls this when it decides take the instance out of service. It is the last
method called n the servlet instance.
Q: What are the different kinds of enterprise beans?
A: Different kind of enterprise beans are Stateless session bean, Stateful session bean, Entity bean,
Message-driven bean...........
Q: What is Session Bean?
A: A session bean is a non-persistent object that implements some business logic running on the
server. One way to think of a session object...........
Q: What is Entity Bean?
A:The entity bean is used to represent data in the database. It provides an object-oriented interface.
Q: What are the methods of Entity Bean?
A: An entity bean consists of 4 groups of methods, create methods...........
Q: What is the difference between Container-Managed Persistent (CMP) bean and Bean-Managed
Persistent(BMP) ?
A: Container-managed persistence (CMP) and bean-managed persistence (BMP). With CMP, the
container manages the persistence of the entity bean............
Collected & Edited By: Gururaj.B.Kulkarni. guruk2k5@gmail.com
Q: What are the callback methods in Entity beans?
A: Callback methods allows the container to notify the bean of events in its life cycle. The callback
methods are defined in the javax.ejb.EntityBean interface............
Q: What is software architecture of EJB?
A: Session and Entity EJBs consist of 4 and 5 parts respectively, a remote interface...........
Q: Can Entity Beans have no create() methods?
A: Yes. In some cases the data is inserted NOT using Java application,...........
Q: What is bean managed transaction?
A: If a developer doesn't want a Container to manage transactions, it's possible to implement all
database operations manually...........
Q: What are transaction attributes?
A: The transaction attribute specifies how the Container must manage transactions for a method
when a client invokes the method via the enterprise bean’s home or...........
Q: What are transaction isolation levels in EJB?
A: Transaction_read_uncommitted , Transaction_read_committed ,
Transaction_repeatable_read...........
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