C,C++ INTERVIEW QUESTIONS

C,C++ Questions

If u want more questions, post the request in comments.
Go through FILE concepts thats the main area where the interviewer will test you.

1. Base class has some virtual method and derived class has a method with the same name. If we initialize the base class pointer with derived
object,. calling of that virtual method will result in which method being called?
a. Base method
b. Derived method..
Ans. b

2. For the following C program
#define AREA(x)(3.14*x*x)
main()
{float r1=6.25,r2=2.5,a;
a=AREA(r1);
printf("\n Area of the circle is %f", a);
a=AREA(r2);
printf("\n Area of the circle is %f", a);
}
What is the output?
Ans. Area of the circle is 122.656250
Area of the circle is 19.625000

3. What do the following statements indicate. Explain.
· int(*p)[10]
· int*f()
· int(*pf)()
· int*p[10]
Refer to:
-- Kernighan & Ritchie page no. 122
-- Schaum series page no. 323

4. void main()
{
int d=5;
printf("%f",d);
}
Ans: Undefined

5.
void main()
{
int i;
for(i=1;i<4,i++)
switch(i)
case 1: printf("%d",i);break;
{
case 2:printf("%d",i);break;
case 3:printf("%d",i);break;
}
switch(i) case 4:printf("%d",i);
}
Ans: 1,2,3,4

6.
void main()
{
char *s="\12345s\n";
printf("%d",sizeof(s));
}
Ans: 6

7.
void main()
{
unsigned i=1; /* unsigned char k= -1 => k=255; */
signed j=-1; /* char k= -1 => k=65535 */
/* unsigned or signed int k= -1 =>k=65535 */
if(i
printf("less");
else
if(i>j)
printf("greater");
else
if(i==j)
printf("equal");
}
Ans: less




8.
void main()
{
float j;
j=1000*1000;
printf("%f",j);
}

1. 1000000
2. Overflow
3. Error
4. None
Ans: 4

9. How do you declare an array of N pointers to functions returning
pointers to functions returning pointers to characters?

Ans: The first part of this question can be answered in at least
three ways:

1. char *(*(*a[N])())();

2. Build the declaration up incrementally, using typedefs:

typedef char *pc; /* pointer to char */
typedef pc fpc(); /* function returning pointer to char */
typedef fpc *pfpc; /* pointer to above */
typedef pfpc fpfpc(); /* function returning... */
typedef fpfpc *pfpfpc; /* pointer to... */
pfpfpc a[N]; /* array of... */

3. Use the cdecl program, which turns English into C and vice
versa:

cdecl> declare a as array of pointer to function returning
pointer to function returning pointer to char
char *(*(*a[])())()

cdecl can also explain complicated declarations, help with
casts, and indicate which set of parentheses the arguments
go in (for complicated function definitions, like the one
above).
Any good book on C should explain how to read these complicated
C declarations "inside out" to understand them ("declaration
mimics use").
The pointer-to-function declarations in the examples above have
not included parameter type information. When the parameters
have complicated types, declarations can *really* get messy.
(Modern versions of cdecl can help here, too.)


10. A structure pointer is defined of the type time . With 3 fields min,sec hours having pointers to intergers.
Write the way to initialize the 2nd element to 10.

11. In the above question an array of pointers is declared.
Write the statement to initialize the 3rd element of the 2 element to 10;

12.
int f()
void main()
{
f(1);
f(1,2);
f(1,2,3);
}
f(int i,int j,int k)
{
printf("%d %d %d",i,j,k);
}

What are the number of syntax errors in the above?

Ans: None.

13.
void main()
{
int i=7;
printf("%d",i++*i++);
}

Ans: 56

14.
#define one 0
#ifdef one
printf("one is defined ");
#ifndef one
printf("one is not defined ");

Ans: "one is defined"




15.
void main()
{
int count=10,*temp,sum=0;
temp=&count;
*temp=20;
temp=∑
*temp=count;
printf("%d %d %d ",count,*temp,sum);
}

Ans: 20 20 20


16. There was question in c working only on unix machine with pattern matching.


14. what is alloca()
Ans : It allocates and frees memory after use/after getting out of scope

17.
main()
{
static i=3;
printf("%d",i--);
return i>0 ? main():0;
}

Ans: 321

18.
char *foo()
{
char result[100]);
strcpy(result,"anything is good");
return(result);
}
void main()
{
char *j;
j=foo()
printf("%s",j);
}

Ans: anything is good.

19.
void main()
{
char *s[]={ "dharma","hewlett-packard","siemens","ibm"};
char **p;
p=s;
printf("%s",++*p);
printf("%s",*p++);
printf("%s",++*p);
}
Ans: "harma" (p->add(dharma) && (*p)->harma)
"harma" (after printing, p->add(hewlett-packard) &&(*p)->harma)
"ewlett-packard"

20. Output of the following program is
main()
{int i=0;
for(i=0;i<20;i++)
{switch(i)
case 0:i+=5;
case 1:i+=2;
case 5:i+=5;
default i+=4;
break;}
printf("%d,",i);
}
}
a) 0,5,9,13,17
b) 5,9,13,17
c) 12,17,22
d) 16,21
e) Syntax error
Ans. (d)

21. What is the ouptut in the following program
main()
{char c=-64;
int i=-32
unsigned int u =-16;
if(c>i)
{printf("pass1,");
if(c
printf("pass2");
else
printf("Fail2");
}
else
printf("Fail1);
if(i
printf("pass2");
else
printf("Fail2")
}
a) Pass1,Pass2
b) Pass1,Fail2
c) Fail1,Pass2
d) Fail1,Fail2
e) None of these
Ans. (c)

22. What will the following program do?
void main()
{
int i;
char a[]="String";
char *p="New Sring";
char *Temp;
Temp=a;
a=malloc(strlen(p) + 1);
strcpy(a,p); //Line number:9//
p = malloc(strlen(Temp) + 1);
strcpy(p,Temp);
printf("(%s, %s)",a,p);
free(p);
free(a);
} //Line number 15//
a) Swap contents of p & a and print:(New string, string)
b) Generate compilation error in line number 8
c) Generate compilation error in line number 5
d) Generate compilation error in line number 7
e) Generate compilation error in line number 1
Ans. (b)

23. In the following code segment what will be the result of the function,
value of x , value of y
{unsigned int x=-1;
int y;
y = ~0;
if(x == y)
printf("same");
else
printf("not same");
}
a) same, MAXINT, -1
b) not same, MAXINT, -MAXINT
c) same , MAXUNIT, -1
d) same, MAXUNIT, MAXUNIT
e) not same, MAXINT, MAXUNIT
Ans. (a)

24. What will be the result of the following program ?
char *gxxx()
{static char xxx[1024];
return xxx;
}
main()
{char *g="string";
strcpy(gxxx(),g);
g = gxxx();
strcpy(g,"oldstring");
printf("The string is : %s",gxxx());
}
a) The string is : string
b) The string is :Oldstring
c) Run time error/Core dump
d) Syntax error during compilation
e) None of these
Ans. (b)

25. Find the output for the following C program
main()
{
char *p1="Name";
char *p2;
p2=(char *)malloc(20);
while(*p2++=*p1++);
printf("%s\n",p2);
}
Ans. An empty string

26. Find the output for the following C program
main()
{
int x=20,y=35;
x = y++ + x++;
y = ++y + ++x;
printf("%d %d\n",x,y);
}
Ans. 57 94

27. Find the output for the following C program
main()
{
int x=5;
printf("%d %d %d\n",x,x<<2,x>>2);
}
Ans. 5 20 1

28 Find the output for the following C program
#define swap1(a,b) a=a+b;b=a-b;a=a-b;
main()
{
int x=5,y=10;
swap1(x,y);
printf("%d %d\n",x,y);
swap2(x,y);
printf("%d %d\n",x,y);
}
int swap2(int a,int b)
{
int temp;
temp=a;
b=a;
a=temp;
return;
}
Ans. 10 5

29 Find the output for the following C program
main()
{
char *ptr = "Ramco Systems";
(*ptr)++;
printf("%s\n",ptr);
ptr++;
printf("%s\n",ptr);
}
Ans. Samco Systems

30 Find the output for the following C program
#include
main()
{
char s1[]="Ramco";
char s2[]="Systems";
s1=s2;
printf("%s",s1);
}
Ans. Compilation error giving it cannot be an modifiable 'lvalue'

31 Find the output for the following C program
#include
main()
{
char *p1;
char *p2;
p1=(char *) malloc(25);
p2=(char *) malloc(25);
strcpy(p1,"Ramco");
strcpy(p2,"Systems");
strcat(p1,p2);
printf("%s",p1);
}
Ans. RamcoSystems

32. Find the output for the following C program given that
[1]. The following variable is available in file1.c
static int average_float;
Ans. All the functions in the file1.c can access the variable

33. Find the output for the following C program
# define TRUE 0
some code
while(TRUE)
{
some code
}
Ans. This won't go into the loop as TRUE is defined as 0

34. struct list{
int x;
struct list *next;
}*head;

the struct head.x =100

Is the above assignment to pointer is correct or wrong ?
Ans. Wrong

35.What is the output of the following ?

int i;
i=1;
i=i+2*i++;
printf(%d,i);
Ans. 4

36. FILE *fp1,*fp2;

fp1=fopen("one","w")
fp2=fopen("one","w")
fputc('A',fp1)
fputc('B',fp2)
fclose(fp1)
fclose(fp2)
}

Find the Error, If Any?
Ans. no error. But It will over writes on same file.

37. What are the output(s) for the following ?
38. #include
char *f()
{char *s=malloc(8);
strcpy(s,"goodbye");
}

main()
{
char *f();
printf("%c",*f()='A'); }


39. #define MAN(x,y) (x)>(y)?(x):(y)
{int i=10;
j=5;
k=0;
k=MAX(i++,++j);
printf(%d %d %d %d,i,j,k);
}
Ans. 10 5 0

40.
void main()
{
int i=7;
printf("%d",i++*i++);
}

Ans: 56

More …..



What is a class?
What is an object?
What is the difference between an object and a class?
What is the difference between class and structure?
What is public, protected, private?
What are virtual functions?
What is friend function?
What is a scope resolution operator?
What do you mean by inheritance?
What is abstraction?
What is polymorphism? Explain with an example.
What is encapsulation?
What do you mean by binding of data and functions?
What is function overloading and operator overloading?
What is virtual class and friend class?
What do you mean by inline function?
What do you mean by public, private, protected and friendly?
When an object created and what is is its lifetime?
What do you mean by multiple inheritance and multilevel inheritance? Differentiate between them.
Difference between realloc()and free?
What is a template?
What are the main differences between procedure oriented languages and object oriented languages?
What is R T T I?
What are generic functions and generic classes?
What is namespace?
What is the difference between pass by reference and pass by value?
Why do we use virtual functions?
What do you mean by pure virtual functions?
What are virtual classes?
Does c++ support multilevel and multiple inheritance ?
What are the advantages of inheritance?
When is a memory allocated to a class?
What is the difference between declaration and definition?
What is virtual constructors/destructors?
In c++ there is only virtual destructors, no constructors. Why?
What is late bound function call and early bound function call? Differentiate.
How is exception handling carried out in c++?
When will a constructor executed?
What is Dynamic Polymorphism?
Write a macro for swapping integers.

JAVA INTERVIEW QUESTIONS with ANSWERS

]

Java Interview Questions with Answers

Core Java, AWT, Swing, RMI, JSP, EJB, JDBC, Servlets, Threads, Java util, JMS, Networking

Question Can there be an abstract class with no abstract methods
in it? (Core Java)
Answer Yes

Question Can an Interface be final? (Core Java)
Answer No

Question Can an Interface have an inner class? (Core Java)
Answer Yes.
public interface abc {
static int i=0;
void dd();
class a1 {
a1() {
int j;
System.out.println("in interfia");
};
public static void main(String a1[]) {
System.out.println("in interfia"); } } }

Question Can we define private and protected modifiers for
variables in interfaces? (Core Java)
Answer No

Question What is the query used to display all tables names in
SQL Server (Query analyzer)? (JDBC)
Answer select * from information_schema.tables

Question What is Externalizable? (Core Java)
Answer Externalizable is an Interface that extends Serializable
Interface. And sends data into Streams in Compressed Format. It has
two methods, writeExternal(ObjectOuput out) and
readExternal(ObjectInput in)

Question What modifiers are allowed for methods in an Interface?
(Core Java)
Answer Only public and abstract modifiers are allowed for
methods in interfaces.

Question What is a local, member and a class variable? (Core
Java)
Answer Variables declared within a method are "local" variables.
Variables declared within the class i.e not within any methods are
"member" variables (global variables).
Variables declared within the class i.e not within any methods and are
defined as "static" are class variables

Question How many types of JDBC Drivers are present and what
are they? (JDBC)
Answer There are 4 types of JDBC Drivers
Type 1: JDBC-ODBC Bridge Driver
Type 2: Native API Partly Java Driver
Type 3: Network protocol Driver
Type 4: JDBC Net pure Java Driver

Question Can we implement an interface in a JSP? (JSP)
Answer No

Question What is the difference between ServletContext and
PageContext? (JSP)
Answer ServletContext: Gives the information about the container
PageContext: Gives the information about the Request

Question What is the difference in using
request.getRequestDispatcher() and
context.getRequestDispatcher()? (JSP)
Answer request.getRequestDispatcher(path): In order to create it
we need to give the relative path of the resource
context.getRequestDispatcher(path): In order to create it we need to
give the absolute path of the resource.

Question How to pass information from JSP to included JSP?
(JSP)
Answer Using <%jsp:param> tag.

Question What is the difference between directive include and jsp
include? (JSP)
Answer <%@ include> : Used to include static resources during
translation time.
: Used to include dynamic content or static content during runtime.

Question What is the difference between RequestDispatcher and
sendRedirect? (JSP)
Answer RequestDispatcher: server-side redirect with request and
response objects.
sendRedirect : Client-side redirect with new request and response
objects.

Question How does JSP handle runtime exceptions? (JSP)
Answer Using errorPage attribute of page directive and also we
need to specify isErrorPage=true if the current page is intended to
URL redirecting of a JSP.

Question How do you delete a Cookie within a JSP? (JSP)
Answer
Cookie mycook = new Cookie("name","value");
response.addCookie(mycook);
Cookie killmycook = new Cookie("mycook","value");
killmycook.setMaxAge(0);
killmycook.setPath("/");
killmycook.addCookie(killmycook);

Question How do I mix JSP and SSI #include? (JSP)
Answer If you’re just including raw HTML, use the #include
directive as usual inside your .jsp file.
But it’s a little trickier if you want the server to evaluate any JSP code
that’s inside the included file. Ronel Sumibcay
(ronel@LIVESOFTWARE.COM) says: If your data.inc file contains
jsp code you will have to use
<%@ vinclude="data.inc" %>
The is used for including non-JSP files.

Question I made my class Cloneable but I still get ’Can’t access
protected method clone. Why? (Core Java)
Answer Yeah, some of the Java books, in particular "The Java
Programming Language", imply that all you have to do in order to
have your class support clone() is implement the Cloneable interface.
Not so. Perhaps that was the intent at some point, but that’s not the
way it works currently. As it stands, you have to implement your own
public clone() method, even if it doesn’t do anything special and just
calls super.clone().

Question Why is XML such an important development? (XML)
Answer It removes two constraints which were holding back Web
developments:
1. dependence on a single, inflexible document type (HTML) which
was being much abused for tasks it was never designed for;
2. the complexity of full SGML, whose syntax allows many powerful
but hard-to-program options. XML allows the flexible development of
user-defined document types. It provides a robust, non-proprietary,
persistent, and verifiable file format for the storage and transmission
of text and data both on and off the Web; and it removes the more
complex options of SGML, making it easier to program for.

Question Are enterprise beans allowed to use Thread.sleep()?
(EJB)
Answer Enterprise beans make use of the services provided by
the EJB container, such as life-cycle management. To avoid conflicts
with these services, enterprise beans are restricted from performing
certain operations: Managing or synchronizing threads

Question Is it possible to write two EJB’s that share the same
Remote and Home interfaces, and have different bean classes? if so,
what are the advantages/disadvantages? (EJB)
Answer It’s certainly possible. In fact, there’s an example that
ships with the Inprise Application Server of an Account interface with
separate implementations for CheckingAccount and SavingsAccount,
one of which was CMP and one of which was BMP.

Question Is it possible to specify multiple JNDI names when
deploying an EJB? (EJB)
Answer No. To achieve this you have to deploy your EJB
multiple times each specifying a different JNDI name.

Question Is there any way to force an Entity Bean to store itself to
the db? I don’t wanna wait for the container to update the db, I want
to do it NOW! Is it possible? (EJB)
Answer Specify the transaction attribute of the bean as
RequiresNew. Then as per section 11.6.2.4 of the EJB v 1.1 spec
EJB container automatically starts a new transaction before the
method call. The container also performs the commit protocol before
the method result is sent to the client.

Question I am developing a BMP Entity bean. I have noticed that
whenever the create method is invoked, the ejbLoad() and the
ejbStore() methods are also invoked. I feel that once my database
insert is done, having to do a select and update SQL queries is major
overhead. is this behavior typical of all EJB containers? Is there any
way to suppress these invocations? (EJB)
Answer This is the default behaviour for EJB. The specification
states that ejbLoad() will be called before every transaction and
ejbStore() after every transaction. Each Vendor has optimizations,
which are proprietary for this scenario.

Question Can an EJB send asynchronous notifications to its
clients? (EJB)
Answer Asynchronous notification is a known hole in the first
versions of the EJB spec. The recommended solution to this is to use
JMS, which is becoming available in J2EE-compliant servers. The
other option, of course, is to use client-side threads and polling. This
is not an ideal solution, but it’s workable for many scenarios.

Question How can I access EJB from ASP? (EJB)
Answer You can use the Java 2 Platform, Enterprise Edition
Client Access Services (J2EETM CAS) COM Bridge 1.0, currently
downloadable from
http://developer.java.sun.com/developer/earlyAccess/j2eecas/

Question Is there a guarantee of uniqueness for entity beans?
(EJB)
Answer There is no such guarantee. The server (or servers) can
instantiate as many instances of the same underlying Entity Bean
(with the same PK) as it wants. However, each instance is
guaranteed to have up-to-date data values, and be transactionally
consistent, so uniqueness is not required. This allows the server to
scale the system to support multiple threads, multiple concurrent
requests, and multiple hosts.

Question How do the six transaction attributes map to isolation
levels like "dirty read"? Will an attribute like "Required" lock out other
readers until I’m finished updating? (EJB)
Answer The Transaction Attributes in EJB do not map to the
Transaction Isolation levels used in JDBC. This is a common
misconception. Transaction Attributes specify to the container when a
Transaction should be started, suspended(paused) and committed
between method invocations on Enterprise JavaBeans. For more
details and a summary of Transaction Attributes refer to section 11.6
of the EJB 1.1 specification.

Question I have created a remote reference to an EJB in
FirstServlet. Can I put the reference in a servlet session and use that
in SecondServlet? (EJB)
Answer Yes. The EJB client (in this case your servlet) acquires a
remote reference to an EJB from the Home Interface; that reference
is serializable and can be passed from servlet to servlet. If it is a
session bean, then the EJB server will consider your web client’s
servlet session to correspond to a single EJB session, which is
usually (but not always) what you want.

Question Can the primary key in the entity bean be a Java
primitive type such as int? (EJB)
Answer The primary key can’t be a primitive type--use the
primitive wrapper classes, instead. For example, you can use
java.lang.Integer as the primary key class, but not int (it has to be a
class, not a primitive)

Question What’s new in the EJB 2.0 specification? (EJB)
Answer Following are the main features supported in EJB 2.0 *
Integration of EJB with JMS * Message Driven Beans * Implement
additional Business methods in Home interface which are not specific
for bean instance. * EJB QL.

Question How many types of protocol implementations does RMI
have? (RMI)
Answer RMI has at least three protocol implementations: Java
Remote Method Protocol(JRMP), Internet Inter ORB Protocol(IIOP),
and Jini Extensible Remote Invocation(JERI). These are alternatives,
not part of the same thing, All three are indeed layer 6 protocols for
those who are still speaking OSI reference model.

Question What are the different identifier states of a Thread?
(Core Java)
Answer The different identifiers of a Thread are:
R - Running or runnable thread
S - Suspended thread
CW - Thread waiting on a condition variable
MW - Thread waiting on a monitor lock
MS - Thread suspended waiting on a monitor lock

Question What is the need of Remote and Home interface. Why
cant it be in one? (EJB)
Answer In a few words, I would say that the main reason is
because there is a clear division of roles and responsabilities
between the two interfaces.
The home interface is your way to communicate with the container,
that is who is responsable of creating, locating even removing one or
more beans.
The remote interface is your link to the bean, that will allow you to
remotely access to all its methods and members.
As you can see there are two distinct elements (the container and the
beans) and you need two different interfaces for accessing to both of
them.

Question What is the difference between Java Beans and EJB?s?
(EJB)
Answer Java Beans are client-side objects and EJBs are server
side object, and they have completely different development,
lifecycle, purpose.

Question With regard to Entity Beans, what happens if
both my EJB Server and Database crash, what will happen to
unsaved changes? Is there any transactional log file used? (EJB)
Answer Actually, if your EJB server crashes, you will not even be
able to make a connection to the server to perform a bean lookup, as
the server will no longer be listening on the port for incoming JNDI
lookup requests. You will lose any data that wasn’t committed prior to
the crash. This is where you should start looking into clustering your
EJB server.
Another Answer
Hi, Any unsaved and uncommited changes are lost the moment your
EJB Server crashes. If your database also crashes, then all the saved
changes are also lost unless you have some backup or some
recovery mechanism to retrieve the data. So consider database
replication and EJB Clustering for such scenarios, though the
occurence of such a thing is very very rare. Thx, Uma All databse
have the concept of log files(for exampe oracle have redo log files
concept). So if data bases crashes then on starting up they fill look up
the log files to perform all pending jobs. But is EJB crashes, It depend
upon the container how frequenlty it passivates or how frequesntly it
refreshes the data with Database.

Question Can you control when passivation occurs? (EJB)
Answer The developer, according to the specification, cannot
directly control when passivation occurs. Although for Stateful
Session Beans, the container cannot passivate an instance that is
inside a transaction. So using transactions can be a a strategy to
control passivation.
The ejbPassivate() method is called during passivation, so the
developer has control over what to do during this exercise and can
implement the require optimized logic.
Some EJB containers, such as BEA WebLogic, provide the ability to
tune the container to minimize passivation calls.
Taken from the WebLogic 6.0 DTD -
"The passivation-strategy can be either "default" or "transaction".
With the default setting the container will attempt to keep a working
set of beans in the cache. With the "transaction" setting, the container
will passivate the bean after every transaction (or method call for a
non-transactional invocation)."

Question Does RMI-IIOP support dynamic downloading of
classes? (RMI)
Answer No, RMI-IIOP doesn’t support dynamic downloading of
the classes as it is done with CORBA in DII (Dynamic Interface
Invocation).Actually RMI-IIOP combines the usability of Java Remote
Method Invocation (RMI) with the interoperability of the Internet Inter-
ORB Protocol (IIOP).So in order to attain this interoperability between
RMI and CORBA,some of the features that are supported by RMI but
not CORBA and vice versa are eliminated from the RMI-IIOP
specification.

Question Does EJB 1.1 support mandate the support for RMI-IIOP
? What is the meaning of "the client API must support the Java RMI_
IIOP programming model for portability, but the underlying protocol
can be anything" ? (EJB)
Answer EJB1.1 does mandate the support of RMI-IIOP.
OK, to Answer the second Question:
There are 2 types of implementations that an EJB Server might
provide: CORBA-based EJB Servers and Proprietry EJB Servers.
Both support the RMI-IIOP API but how that API is implemented is a
different story. (NB: By API we mean the interface provided to the
client by the stub or proxy).
A CORBA-based EJB Server actually implements its EJB Objects as
CORBA Objects (it therefore encorporates an ORB and this means
that EJB’s can be contacted by CORBA clients (as well as RMI-IIOP
clients)
A proprietry EJB still implements the RMI-IIOP API (in the client’s
stub) but the underlying protocol can be anything. Therefore your
EJB’s CANNOT be contacted by CORBA clients. The difference is
that in both cases, your clients see the same API (hence, your client
portability) BUT how the stubs communicate with the server is
different.

Question The EJB specification says that we cannot use Bean
Managed Transaction in Entity Beans. Why? (EJB)
Answer The short, practical Answer is... because it makes your
entity beans useless as a reusable component. Also, transaction
management is best left to the application server - that’s what they’re
there for. It’s all about atomic operations on your data. If an operation
updates more than one entity then you want the whole thing to
succeed or the whole thing to fail, nothing in between. If you put
commits in the entity beans then it’s very difficult to rollback if an error
occurs at some point late in the operation.

Question Can I invoke Runtime.gc() in an EJB? (EJB)
Answer You shouldn’t.
What will happen depends on the implementation, but the call will
most likely be ignored. You should leave system level management
like garbage collection for the container to deal with. After all, that’s
part of the benefit of using EJBs, you don’t have to manage
resources yourself.

Question What is clustering? What are the different algorithms
used for clustering? (EJB)
Answer Clustering is grouping machines together to
transparantly provide enterprise services.The client does not now the
difference between approaching one server or approaching a cluster
of servers.Clusters provide two benefits: scalability and high
availability. Further information can be found in the JavaWorld article
J2EE Clustering.

Question What is the advantage of using Entity bean for database
operations, over directly using JDBC API to do database operations?
When would I use one over the other? (EJB)
Answer Entity Beans actually represents the data in a database.
It is not that Entity Beans replaces JDBC API. There are two types of
Entity Beans Container Managed and Bean Mananged. In Container
Managed Entity Bean - Whenever the instance of the bean is created
the container automatically retrieves the data from the
DB/Persistance storage and assigns to the object variables in bean
for user to manipulate or use them. For this the developer needs to
map the fields in the database to the variables in deployment
descriptor files (which varies for each vendor).
In the Bean Managed Entity Bean - The developer has to specifically
make connection, retrive values, assign them to the objects in the
ejbLoad() which will be called by the container when it instatiates a
bean object. Similarly in the ejbStore() the container saves the object
values back the the persistance storage. ejbLoad and ejbStore are
callback methods and can be only invoked by the container. Apart
from this, when you use Entity beans you dont need to worry about
database transaction handling, database connection pooling etc.
which are taken care by the ejb container. But in case of JDBC you
have to explicitly do the above features. what suresh told is exactly
perfect. ofcourse, this comes under the database transations, but i
want to add this. the great thing about the entity beans of container
managed, whenever the connection is failed during the transaction
processing, the database consistancy is mantained automatically. the
container writes the data stored at persistant storage of the entity
beans to the database again to provide the database consistancy.
where as in jdbc api, we, developers has to do manually.

Question What is the role of serialization in EJB? (EJB)
Answer A big part of EJB is that it is a framework for underlying
RMI: remote method invocation. You’re invoking methods remotely
from JVM space ’A’ on objects which are in JVM space ’B’ -- possibly
running on another machine on the network.
To make this happen, all arguments of each method call must have
their current state plucked out of JVM ’A’ memory, flattened into a
byte stream which can be sent over a TCP/IP network connection,
and then deserialized for reincarnation on the other end in JVM ’B’
where the actual method call takes place.
If the method has a return value, it is serialized up for streaming back
to JVM A. Thus the requirement that all EJB methods arguments and
return values must be serializable. The easiest way to do this is to
make sure all your classes implement java.io.Serializable.

Question What is EJB QL? (EJB)
Answer EJB QL is a Query Language provided for navigation
across a network of enterprise beans and dependent objects defined
by means of container managed persistence. EJB QL is introduced in
the EJB 2.0 specification. The EJB QL query language defines finder
methods for entity beans with container managed persistenceand is
portable across containers and persistence managers. EJB QL is
used for queries of two types of finder methods: Finder methods that
are defined in the home interface of an entity bean and which return
entity objects. Select methods, which are not exposed to the client,
but which are used by the Bean Provider to select persistent values
that are maintained by the Persistence Manager or to select entity
objects that are related to the entity bean on which the query is
defined.

Question What is the fastest type of JDBC driver? (JDBC)
Answer JDBC driver performance will depend on a number of
issues:
(a) the quality of the driver code,
(b) the size of the driver code,
(c) the database server and its load,
(d) network topology,
(e) the number of times your request is translated to a different API.
In general, all things being equal, you can assume that the more your
request and response change hands, the slower it will be. This
means that Type 1 and Type 3 drivers will be slower than Type 2
drivers (the database calls are make at least three translations versus
two), and Type 4 drivers are the fastest (only one translation).

Question Request parameter How to find whether a parameter
exists in the request object? (Servlets)
Answer 1.boolean hasFoo = !(request.getParameter("foo") ==
null || request.getParameter("foo").equals(""));
2. boolean hasParameter =
request.getParameterMap().contains(theParameter);
(which works in Servlet 2.3+)

Question How can I send user authentication information while
makingURLConnection? (Servlets)
Answer You’ll want to use
HttpURLConnection.setRequestProperty and set all the appropriate
headers to HTTP authorization.

Question What are some alternatives to inheritance? (Core Java)
Answer Delegation is an alternative to inheritance. Delegation
means that you include an instance of another class as an instance
variable, and forward messages to the instance. It is often safer than
inheritance because it forces you to think about each message you
forward, because the instance is of a known class, rather than a new
class, and because it doesn’t force you to accept all the methods of
the super class: you can provide only the methods that really make
sense. On the other hand, it makes you write more code, and it is
harder to re-use (because it is not a subclass).

Question Why isn’t there operator overloading? (Core Java)
Answer Because C++ has proven by example that operator
overloading makes code almost impossible to maintain. In fact there
very nearly wasn’t even method overloading in Java, but it was
thought that this was too useful for some very basic methods like
print(). Note that some of the classes like DataOutputStream have
unoverloaded methods like writeInt() and writeByte().

Question What does it mean that a method or field is "static"?
(Core Java)
Answer Static variables and methods are instantiated only once
per class. In other words they are class variables, not instance
variables. If you change the value of a static variable in a particular
object, the value of that variable changes for all instances of that
class.
Static methods can be referenced with the name of the class rather
than the name of a particular object of the class (though that works
too). That’s how library methods like System.out.println() work. out is
a static field in the java.lang.System class.

Question How do I convert a numeric IP address like 192.18.97.39
into a hostname like java.sun.com? (Networking)
Answer String hostname =
InetAddress.getByName("192.18.97.39").getHostName();

Question Difference between JRE And JVM AND JDK (Core
Java)

Question Why do threads block on I/O? (Core Java)
Answer Threads block on i/o (that is enters the waiting state) so
that other threads may execute while the i/o Operation is performed.

Question What is synchronization and why is it important? (Core
Java)
Answer 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.

Question Is null a keyword? (Core Java)
Answer The null value is not a keyword.

Question Which characters may be used as the second character
of an identifier,but not as the first character of an identifier? (Core
Java)
Answer The digits 0 through 9 may not be used as the first
character of an identifier but they may be used after the first character
of an identifier.

Question What modifiers may be used with an inner class that is a
member of an outer class? (Core Java)
Answer A (non-local) inner class may be declared as public,
protected, private, static, final, or abstract.

Question How many bits are used to represent Unicode, ASCII,
UTF-16, and UTF-8 characters? (Core Java)
Answer Unicode requires 16 bits and ASCII require 7 bits.
Although the ASCII character set uses only 7 bits, it is usually
represented as 8 bits. UTF-8 represents characters using 8, 16, and
18 bit patterns. UTF-16 uses 16-bit and larger bit patterns.

Question What are wrapped classes? (Core Java)
Answer Wrapped classes are classes that allow primitive types
to be accessed as objects.

Question What restrictions are placed on the location of a
package statement within a source code file? (Core Java)
Answer A package statement must appear as the first line in a
source code file (excluding blank lines and comments).

Question What is the difference between preemptive scheduling
and time slicing? (Core Java)
Answer 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.

Question What is a native method? (Core Java)
Answer A native method is a method that is implemented in a
language other than Java.

Question What are order of precedence and associativity, and
how are they used? (Core Java)
Answer Order of precedence determines the order in which
operators are evaluated in expressions. Associatity determines
whether an expression is evaluated left-to-right or right-to-left

Question What is the catch or declare rule for method
declarations? (Core Java)
Answer If a checked exception may be thrown within the body of
a method, the method must either catch the exception or declare it in
its throws clause.

Question Can an anonymous class be declared as implementing
an interface and extending a class? (Core Java)
Answer An anonymous class may implement an interface or
extend a superclass, but may not be declared to do both.

Question What is the range of the char type? (Core Java)
Answer The range of the char type is 0 to 2^16 - 1.

Question What is the purpose of finalization? (Core Java)
Answer The purpose of finalization is to give an unreachable
object the opportunity to perform any cleanup processing before the
object is garbage collected.

Question What is the difference between the Boolean & operator
and the && operator? (Core Java)
Answer If an expression involving the Boolean & operator is
evaluated, both operands are evaluated. Then the & operator is
applied to the operand. When an expression involving the &&
operator is evaluated, the first operand is evaluated. If the first
operand returns a value of true then the second operand is
evaluated. The && operator is then applied to the first and second
operands. If the first operand evaluates to false, the evaluation of the
second operand is skipped.

Question How many times may an object’s finalize() method be
invoked by the garbage collector? (Core Java)
Answer An object’s finalize() method may only be invoked once
by the garbage collector.

Question What is the purpose of the finally clause of a try-catchfinally
statement? (Core Java)
Answer The finally clause is used to provide the capability to
execute code no matter whether or not an exception is thrown or
caught.

Question What is the argument type of a program’s main()
method? (Core Java)
Answer A program’s main() method takes an argument of the
String[] type.

Question Which Java operator is right associative? (Core Java)
Answer The = operator is right associative.

Question Can a double value be cast to a byte? (Core Java)
Answer Yes, a double value can be cast to a byte.

Question What is the difference between a break statement and a
continue statement? (Core Java)
Answer A break statement results in the termination of the
statement to which it applies (switch, for, do, or while). A continue
statement is used to end the current loop iteration and return control
to the loop statement.

Question What must a class do to implement an interface? (Core
Java)
Answer It must provide all of the methods in the interface and
identify the interface in its implements clause.

Question What is the advantage of the event-delegation model
over the earlier event-inheritance model? (Core Java)
Answer The event-delegation model has two advantages over
the event-inheritance model. First, it enables event handling to be
handled by objects other than the ones that generate the events (or
their containers). This allows a clean separation between a
component’s design and its use. The other advantage of the eventdelegation
model is that it performs much better in applications where
many events are generated. This performance improvement is due to
the fact that the event-delegation model does not have to repeatedly
process unhandled events, as is the case of the event-inheritance
model.

Question How are commas used in the intialization and iteration
parts of a for statement? (Core Java)
Answer Commas are used to separate multiple statements
within the initialization and iteration parts of a for statement.

Question What is an abstract method? (Core Java)
Answer An abstract method is a method whose implementation
is deferred to a subclass.

Question What value does read() return when it has reached the
end of a file? (Core Java)
Answer The read() method returns -1 when it has reached the
end of a file.

Question Can a Byte object be cast to a double value? (Core
Java)
Answer No, an object cannot be cast to a primitive value.

Question What is the difference between a static and a non-static
inner class? (Core Java)
Answer A non-static inner class may have object instances that
are associated with instances of the class’s outer class. A static inner
class does not have any object instances.

Question If a variable is declared as private, where may the
variable be accessed? (Core Java)
Answer A private variable may only be accessed within the class
in which it is declared.

Question What is an object’s lock and which object’s have locks?
(Core Java)
Answer An object’s lock is a mechanism that is used by multiple
threads to obtain synchronized access to the object. A thread may
execute a synchronized method of an object only after it has acquired
the object’s lock. All objects and classes have locks. A class’s lock is
acquired on the class’s Class object.

Question What is the % operator? (Core Java)
Answer It is referred to as the modulo or remainder operator. It
returns the remainder of dividing the first operand by the second
operand.

Question When can an object reference be cast to an interface
reference? (Core Java)
Answer An object reference be cast to an interface reference
when the object implements the referenced interface.

Question Which class is extended by all other classes? (Core
Java)
Answer The Object class is extended by all other classes.

Question Can an object be garbage collected while it is still
reachable? (Core Java)
Answer A reachable object cannot be garbage collected. Only
unreachable objects may be garbage collected.

Question Is the ternary operator written x : y ? z or x ? y : z ?
(Core Java)
Answer It is written x ? y : z.

Question How is rounding performed under integer division?
(Core Java)
Answer The fractional part of the result is truncated. This is
known as rounding toward zero.

Question What is the difference between the Reader/Writer class
hierarchy and the InputStream/OutputStream class hierarchy? (Core
Java)
Answer The Reader/Writer class hierarchy is character-oriented,
and the InputStream/OutputStream class hierarchy is byte-oriented.

Question What classes of exceptions may be caught by a catch
clause? (Core Java)
Answer A catch clause can catch any exception that may be
assigned to the Throwable type. This includes the Error and
Exception types.

Question If a class is declared without any access modifiers,
where may the class be accessed? (Core Java)
Answer A class that is declared without any access modifiers is
said to have package access. This means that the class can only be
accessed by other classes and interfaces that are defined within the
same package.

Question Does a class inherit the constructors of its superclass?
(Core Java)
Answer A class does not inherit constructors from any of its
superclasses.

Question What is the purpose of the System class? (Core Java)
Answer The purpose of the System class is to provide access to
system resources.

Question Name the eight primitive Java types. (Core Java)
Answer The eight primitive types are byte, char, short, int, long,
float, double, and boolean.

Question Which class should you use to obtain design information
about an object? (Core Java)
Answer The Class class is used to obtain information about an
object’s design.

Question Is "abc" a primitive value? (Core Java)
Answer The String literal "abc" is not a primitive value. It is a
String object.

Question What restrictions are placed on the values of each case
of a switch statement? (Core Java)
Answer During compilation, the values of each case of a switch
statement must evaluate to a value that can be promoted to an int
value.

Question What modifiers may be used with an interface
declaration? (Core Java)
Answer An interface may be declared as public or abstract.

Question Is a class a subclass of itself? (Core Java)
Answer A class is a subclass of itself.

Question What is the difference between a while statement and a
do statement? (Core Java)
Answer 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.

Question What modifiers can be used with a local inner class?
(Core Java)
Answer A local inner class may be final or abstract.

Question What is the purpose of the File class? (Core Java)
Answer The File class is used to create objects that provide
access to the files and directories of a local file system.

Question Can an exception be rethrown? (Core Java)
Answer Yes, an exception can be rethrown.

Question When does the compiler supply a default constructor for
a class? (Core Java)
Answer The compiler supplies a default constructor for a class if
no other constructors are provided.

Question If a method is declared as protected, where may the
method be accessed? (Core Java)
Answer A protected method may only be accessed by classes or
interfaces of the same package or by subclasses of the class in which
it is declared.

Question Which non-Unicode letter characters may be used as
the first character of an identifier? (Core Java)
Answer The non-Unicode letter characters $ and _ may appear
as the first character of an identifier

Question What restrictions are placed on method overloading?
(Core Java)
Answer Two methods may not have the same name and
argument list but different return types.

Question What is casting? (Core Java)
Answer There are two types of casting, casting between
primitive numeric types and casting between object references.
Casting between numeric types is used to convert larger values, such
as double values, to smaller values, such as byte values. Casting
between object references is used to refer to an object by a
compatible class, interface, or array type reference.

Question What is the return type of a program’s main() method?
(Core Java)
Answer A program’s main() method has a void return type.

Question What class of exceptions are generated by the Java runtime
system? (Core Java)
Answer The Java runtime system generates RuntimeException
and Error exceptions.

Question What class allows you to read objects directly from a
stream? (Core Java)
Answer The ObjectInputStream class supports the reading of
objects from input streams.

Question What is the difference between a field variable and a
local variable? (Core Java)
Answer A field variable is a variable that is declared as a
member of a class. A local variable is a variable that is declared local
to a method.

Question How are this() and super() used with constructors?
(Core Java)
Answer this() is used to invoke a constructor of the same class.
super() is used to invoke a superclass constructor.

Question What is the relationship between a method’s throws
clause and the exceptions that can be thrown during the method’s
execution? (Core Java)
Answer A method’s throws clause must declare any checked
exceptions that are not caught within the body of the method.

Question Why are the methods of the Math class static? (Core
Java)
Answer So they can be invoked as if they are a mathematical
code library.

Question What are the legal operands of the instanceof operator?
(Core Java)
Answer The left operand is an object reference or null value and
the right operand is a class, interface, or array type.

Question What an I/O filter? (Core Java)
Answer An I/O filter is an object that reads from one stream and
writes to another, usually altering the data in some way as it is
passed from one stream to another.

Question If an object is garbage collected, can it become
reachable again? (Core Java)
Answer Once an object is garbage collected, it ceases to exist. It
can no longer become reachable again.

Question What are E and PI? (Core Java)
Answer E is the base of the natural logarithm and PI is
mathematical value pi.

Question Are true and false keywords? (Core Java)
Answer The values true and false are not keywords.

Question What is the difference between the File and
RandomAccessFile classes? (Core Java)
Answer The File class encapsulates the files and directories of
the local file system. The RandomAccessFile class provides the
methods needed to directly access data contained in any part of a
file.

Question What happens when you add a double value to a String?
(Core Java)
Answer The result is a String object.

Question What is your platform’s default character encoding?
(Core Java)
Answer If you are running Java on English Windows platforms, it
is probably Cp1252. If you are running Java on English Solaris
platforms, it is most likely 8859_1.

Question Which package is always imported by default? (Core
Java)
Answer The java.lang package is always imported by default.

Question What interface must an object implement before it can
be written to a stream as an object? (Core Java)
Answer An object must implement the Serializable or
Externalizable interface before it can be written to a stream as an
object.

Question How can my application get to know when a HttpSession
is removed? (JSP)
Answer Define a Class HttpSessionNotifier which implements
HttpSessionBindingListener and implement the functionality what you
need in valueUnbound() method.
Create an instance of that class and put that instance in HttpSession.

Question Whats the difference between notify() and notifyAll()?
(Core Java)
Answer notify() is used to unblock one waiting thread; notifyAll()
is used to unblock all of them. Using notify() is preferable (for
efficiency) when only one blocked thread can benefit from the change
(for example, when freeing a buffer back into a pool). notifyAll() is
necessary (for correctness) if multiple threads should resume (for
example, when releasing a "writer" lock on a file might permit all
"readers" to resume).

Question What is the difference between logical data
independence and physical data independence? (Core Java)
Answer Logical Data Independence - meaning immunity of
external schemas to changeds in conceptual schema. Physical Data
Independence - meaning immunity of conceptual schema to changes
in the internal schema.

Question What is user defined exception? (Core Java)
Answer Apart from the exceptions already defined in Java
package libraries, user can define his own exception classes by
extending Exception class.

Question Why can’t I say just abs() or sin() instead of Math.abs()
and Math.sin()? (Core Java)
Answer The import statement does not bring methods into your
local name space. It lets you abbreviate class names, but not get rid
of them altogether. That’s just the way it works, you’ll get used to it.
It’s really a lot safer this way.
However, there is actually a little
trick you can use in some cases that gets you what you want. If your
top-level class doesn’t need to inherit from anything else, make it
inherit from java.lang.Math. That *does* bring all the methods into
your local name space. But you can’t use this trick in an applet,
because you have to inherit from java.awt.Applet. And actually, you
can’t use it on java.lang.Math at all, because Math is a "final" class
which means it can’t be extended.

Question Wha is the output from System.out.println("Hello"+null);
(Core Java)
Answer Hellonull

Question Can we use the constructor, instead of init(), to initialize
servlet? (Servlets)
Answer Yes , of course you can use the constructor instead of
init(). There’s nothing to stop you. But you shouldn’t. The original
reason for init() was that ancient versions of Java couldn’t
dynamically invoke constructors with arguments, so there was no way
to give the constructur a ServletConfig. That no longer applies, but
servlet containers still will only call your no-arg constructor. So you
won’t have access to a ServletConfig or ServletContext.

Question How can a servlet refresh automatically if some new
data has entered the database? (Servlets)
Answer You can use a client-side Refresh or Server Push

Question The code in a finally clause will never fail to execute,
right? (Servlets)
Answer Using System.exit(1); in try block will not allow finally
code to execute.

Question Why are there no global variables in Java? (Core Java)
Answer Global variables are considered bad form for a variety of
reasons:
. Adding state variables breaks referential transparency (you no
longer can understand a statement or expression on its own: you
need to understand it in the context of the settings of the global
variables).
. State variables lessen the cohesion of a program: you need to know
more to understand how something works. A major point of Object-
Oriented programming is to break up global state into more easily
understood collections of local state.
. When you add one variable, you limit the use of your program to
one instance. What you thought was global, someone else might
think of as local: they may want to run two copies of your program at
once.
For these reasons, Java decided to ban global variables.

Question What does it mean that a class or member is final?
(Core Java)
Answer A final class can no longer be subclassed. Mostly this is
done for security reasons with basic classes like String and Integer. It
also allows the compiler to make some optimizations, and makes
thread safety a little easier to achieve.
Methods may be declared final as well. This means they may not be
overridden in a subclass.
Fields can be declared final, too. However, this has a completely
different meaning. A final field cannot be changed after it’s initialized,
and it must include an initializer statement where it’s declared. For
example,
public final double c = 2.998;
It’s also possible to make a static field final to get the effect of C++’s
const statement or some uses of C’s #define, e.g.
public static final double c = 2.998;

Question What does it mean that a method or class is abstract?
(Core Java)
Answer An abstract class cannot be instantiated. Only its
subclasses can be instantiated. You indicate that a class is abstract
with the abstract keyword like this:
public abstract class Container extends Component {
Abstract classes may contain abstract methods. A method declared
abstract is not actually implemented in the current class. It exists only
to be overridden in subclasses. It has no body. For example,
public abstract float price();
Abstract methods may only be included in abstract classes. However,
an abstract class is not required to have any abstract methods,
though most of them do.
Each subclass of an abstract class must override the abstract
methods of its superclasses or itself be declared abstract.

Question what is a transient variable? (Core Java)
Answer transient variable is a variable that may not be
serialized.

Question How are Observer and Observable used? (Core Java)
Answer 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.

Question Can a lock be acquired on a class? (Core Java)
Answer Yes, a lock can be acquired on a class. This lock is
acquired on the class’s Class object.

Question What state does a thread enter when it terminates its
processing? (Core Java)
Answer When a thread terminates its processing, it enters the
dead state.

Question How does Java handle integer overflows and
underflows? (Core Java)
Answer It uses those low order bytes of the result that can fit into
the size of the type allowed by the operation.

Question What is the difference between the >> and >>>
operators? (Core Java)
Answer The >> operator carries the sign bit when shifting right.
The >>> zero-fills bits that have been shifted out.

Question Is sizeof a keyword? (Core Java)
Answer The sizeof operator is not a keyword.

Question Does garbage collection guarantee that a program will
not run out of memory? (Core Java)
Answer 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

Question Can an object’s finalize() method be invoked while it is
reachable? (Core Java)
Answer An object’s finalize() method cannot be invoked by the
garbage collector while the object is still reachable. However, an
object’s finalize() method may be invoked by other objects.

Question What value does readLine() return when it has reached
the end of a file? (Core Java)
Answer The readLine() method returns null when it has reached
the end of a file.

Question Can a for statement loop indefinitely? (Core Java)
Answer Yes, a for statement can loop indefinitely. For example,
consider the following: for(;;) ;

Question To what value is a variable of the String type
automatically initialized? (Core Java)
Answer The default value of an String type is null.

Question What is a task’s priority and how is it used in
scheduling? (Core Java)
Answer A task’s priority is an integer value that identifies the
relative order in which it should be executed with respect to other
tasks. The scheduler attempts to schedule higher priority tasks before
lower priority tasks.

Question What is the range of the short type? (Core Java)
Answer The range of the short type is -(2^15) to 2^15 - 1.

Question What is the purpose of garbage collection? (Core Java)
Answer The purpose of garbage collection is to identify and
discard objects that are no longer needed by a program so that their
resources may be reclaimed and reused.


Question Is is possible for an EJB client to marshall an object of
class java.lang.Class to an EJB? (EJB)
Answer Technically yes, spec. compliant NO! - The enterprise
bean must not attempt to query a class to obtain information about
the declared members that are not otherwise accessible to the
enterprise bean because of the security rules of the Java language.

Question Is it legal to have static initializer blocks in EJB? (EJB)
Answer Although technically it is legal, static initializer blocks are
used to execute some piece of code before executing any constructor
or method while instantiating a class. Static initializer blocks are also
typically used to initialize static fields - which may be illegal in EJB if
they are read/write - In EJB this can be achieved by including the
code in either the ejbCreate(), setSessionContext() or
setEntityContext() methods.

Question How can I implement a thread-safe JSP page? (JSP)
Answer You can make your JSPs thread-safe by having them
implement the SingleThreadModel interface. This is done by adding
the directive <%@ page isThreadSafe="false" % > within your JSP
page.

Question Is it possible to stop the execution of a method before
completion in a SessionBean? (EJB)
Answer Stopping the execution of a method inside a Session
Bean is not possible without writing code inside the Session Bean.
This is because you are not allowed to access Threads inside an
EJB.

Question What is the default transaction attribute for an EJB?
(EJB)
Answer There is no default transaction attribute for an EJB.
Section 11.5 of EJB v1.1 spec says that the deployer must specify a
value for the transaction attribute for those methods having container
managed transaction. In weblogic, the default transaction attribute for
EJB is SUPPORTS.

Question What is the difference between session and entity
beans? When should I use one or the other? (EJB)
Answer An entity bean represents persistent global data from the
database; a session bean represents transient user-specific data that
will die when the user disconnects (ends his session). Generally, the
session beans implement business methods (e.g.
Bank.transferFunds) that call entity beans (e.g. Account.deposit,
Account.withdraw)

Question Is there any default cache management system with
Entity beans ? In other words whether a cache of the data in
database will be maintained in EJB ? (EJB)
Answer Caching data from a database inside the Application
Server are what Entity EJB’s are used for.The ejbLoad() and
ejbStore() methods are used to synchronize the Entity Bean state
with the persistent storage(database). Transactions also play an
important role in this scenario. If data is removed from the database,
via an external application - your Entity Bean can still be "alive" the
EJB container. When the transaction commits, ejbStore() is called
and the row will not be found, and the transcation rolled back.

Question Why is ejbFindByPrimaryKey mandatory? (EJB)
Answer An Entity Bean represents persistent data that is stored
outside of the EJB Container/Server. The ejbFindByPrimaryKey is a
method used to locate and load an Entity Bean into the container,
similar to a SELECT statement in SQL. By making this method
mandatory, the client programmer can be assured that if they have
the primary key of the Entity Bean, then they can retrieve the bean
without having to create a new bean each time - which would mean
creating duplications of persistent data and break the integrity of EJB.

Question Why do we have a remove method in both EJBHome
and EJBObject? (EJB)
Answer With the EJBHome version of the remove, you are able
to delete an entity bean without first instantiating it (you can provide a
PrimaryKey object as a parameter to the remove method). The home
version only works for entity beans. On the other hand, the Remote
interface version works on an entity bean that you have already