Interview
Questions in Core Java
1.what is a
transient variable?
A transient variable is a
variable that may not be serialized.
2.which
containers use a border Layout as their default layout?
The window, Frame and Dialog
classes use a border layout as their default layout.
3.Why do threads
block on I/O?
Threads block on i/o (that is
enters the waiting state) so that other threads may execute while the i/o
Operation is performed.
4. How are
Observer and Observable used?
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.
5. What is
synchronization and why is it important?
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.
6. Can a lock be
acquired on a class?
Yes, a lock can be acquired on a
class. This lock is acquired on the class's Class object.
7. What's new
with the stop(), suspend() and resume() methods in JDK 1.2?
The stop(), suspend() and
resume() methods have been deprecated in JDK 1.2.
8. Is null a
keyword?
The null value is not a keyword.
9. What is the
preferred size of a component?
The preferred size of a component
is the minimum component size that will allow the component to display
normally.
10. What method
is used to specify a container's layout?
The setLayout() method is used to
specify a container's layout.
11. Which
containers use a FlowLayout as their default layout?
The Panel and Applet classes use
the FlowLayout as their default layout.
12. What state
does a thread enter when it terminates its processing?
When a thread terminates its
processing, it enters the dead state.
13. What is the
Collections API?
The Collections API is a set of
classes and interfaces that support operations on collections of objects.
14. Which
characters may be used as the second character of an identifier, but not as the
first
character of an
identifier?
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.
15. What is the
List interface?
The List interface provides
support for ordered collections of objects.
16. How does
Java handle integer overflows and underflows?
It uses those low order bytes of
the result that can fit into the size of the type allowed by the operation.
17. What is the
Vector class?
The Vector class provides the
capability to implement a growable array of objects
18. What
modifiers may be used with an inner class that is a member of an outer class?
A (non-local) inner class may be
declared as public, protected, private, static, final, or abstract.
19. What is an
Iterator interface?
The Iterator interface is used to
step through the elements of a Collection.
20. What is the
difference between the >> and >>> operators?
The >> operator carries the
sign bit when shifting right. The >>> zero-fills bits that have been
shifted out.
21. Which method
of the Component class is used to set the position and size of a component?
setBounds()
22. How many
bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters?
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.
23What is the
difference between yielding and sleeping?
When a task invokes its yield()
method, it returns to the ready state. When a task invokes its sleep()
method, it returns to the waiting
state.
24. Which
java.util classes and interfaces support event handling?
The EventObject class and the
EventListener interface support event processing.
25. Is sizeof a
keyword?
The sizeof operator is not a
keyword.
26. What are
wrapped classes?
Wrapped classes are classes that
allow primitive types to be accessed as objects.
27. Does garbage
collection guarantee that a program will not run out of memory?
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
28. What
restrictions are placed on the location of a package statement within a source
code file?
A package statement must appear
as the first line in a source code file (excluding blank lines and
comments).
29. Can an
object's finalize() method be invoked while it is reachable?
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.
30. What is the
immediate superclass of the Applet class?
Panel
31. What is the
difference between preemptive scheduling and time slicing?
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.
32. Name three
Component subclasses that support painting.
The Canvas, Frame, Panel, and
Applet classes support painting.
33. What value does
readLine() return when it has reached the end of a file?
The readLine() method returns
null when it has reached the end of a file.
34. What is the
immediate superclass of the Dialog class?
Window
35. What is
clipping?
Clipping is the process of confining
paint operations to a limited area or shape.
36. What is a
native method?
A native method is a method that
is implemented in a language other than Java.
37. Can a for
statement loop indefinitely?
Yes, a for statement can loop
indefinitely. For example, consider the following:
for(;;) ;
38. What are
order of precedence and associativity, and how are they used?
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
39. When a
thread blocks on I/O, what state does it enter?
A thread enters the waiting state
when it blocks on I/O.
40. To what
value is a variable of the String type automatically initialized?
The default value of an String
type is null.
41. What is the
catch or declare rule for method declarations?
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.
42. What is the
difference between a MenuItem and a CheckboxMenuItem?
The CheckboxMenuItem class
extends the MenuItem class to support a menu item that may be checked or
unchecked.
43. What is a
task's priority and how is it used in scheduling?
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.
44. What class
is the top of the AWT event hierarchy?
The java.awt.AWTEvent class is
the highest-level class in the AWT event-class hierarchy.
45. When a
thread is created and started, what is its initial state?
A thread is in the ready state
after it has been created and started.
46. Can an
anonymous class be declared as implementing an interface and extending a class?
An anonymous class may implement
an interface or extend a superclass, but may not be declared to do
both.
47. What is the
range of the short type?
The range of the short type is
-(2^15) to 2^15 - 1.
48. What is the
range of the char type?
The range of the char type is 0
to 2^16 - 1.
49. In which
package are most of the AWT events that support the event-delegation model
defined?
Most of the AWT-related events of
the event-delegation model are defined in the java.awt.event package.
The AWTEvent class is defined in
the java.awt package.
50. What is the
immediate superclass of Menu?
MenuItem
51. What is the
purpose of finalization?
The purpose of finalization is to
give an unreachable object the opportunity to perform any cleanup
processing before the object is
garbage collected.
52. Which class
is the immediate superclass of the MenuComponent class.
Object
53. What invokes
a thread's run() method?
After a thread is started, via
its start() method or that of the Thread class, the JVM invokes the thread's
run() method when the thread is
initially executed.
54. What is the
difference between the Boolean & operator and the && operator?
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.
55. Name three
subclasses of the Component class.
Box.Filler, Button, Canvas,
Checkbox, Choice, Container, Label, List, Scrollbar, or TextComponent
56. What is the
GregorianCalendar class?
The GregorianCalendar provides
support for traditional Western calendars.
57. Which
Container method is used to cause a container to be laid out and redisplayed?
validate()
58. What is the
purpose of the Runtime class?
The purpose of the Runtime class
is to provide access to the Java runtime system.
59. How many
times may an object's finalize() method be invoked by the garbage collector?
An object's finalize() method may
only be invoked once by the garbage collector.
60. What is the
purpose of the finally clause of a try-catch-finally statement?
The finally clause is used to
provide the capability to execute code no matter whether or not an exception is
thrown or caught.
61. What is the
argument type of a program's main() method?
A program's main() method takes
an argument of the String[] type.
62. Which Java
operator is right associative?
The = operator is right
associative.
63. What is the
Locale class?
The Locale class is used to
tailor program output to the conventions of a particular geographic, political,
or
cultural region.
64. Can a double
value be cast to a byte?
Yes, a double value can be cast
to a byte.
65. What is the
difference between a break statement and a continue statement?
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.
66. What must a
class do to implement an interface?
It must provide all of the
methods in the interface and identify the interface in its implements clause.
67. What method
is invoked to cause an object to begin executing as a separate thread?
The start() method of the Thread
class is invoked to cause an object to begin executing as a separate thread.
68. Name two
subclasses of the TextComponent class.
TextField and TextArea
69. What is the
advantage of the event-delegation model over the earlier event-inheritance
model?
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.
70. Which
containers may have a MenuBar?
Frame
71. How are commas
used in the initialization and iteration parts of a for statement?
Commas are used to separate
multiple statements within the initialization and iteration parts of a for
statement.
72. What is the
purpose of the wait(), notify(), and notifyAll() methods?
The wait(),notify(), and
notifyAll() methods are used to provide an efficient way for threads to wait
for a
shared resource. When a thread
executes an object's wait() method, it enters the waiting state. It only enters
the ready state after another thread
invokes the object's notify() or notifyAll() methods.
73. What is an
abstract method?
An abstract method is a method
whose implementation is deferred to a subclass.
74. How are Java
source code files named?
A Java source code file takes the
name of a public class or interface that is defined within the file. A source
code file may contain at most one
public class or interface. If a public class or interface is defined within a
source code file, then the source
code file must take the name of the public class or interface. If no public
class or interface is defined
within a source code file, then the file must take on a name that is different
than
its classes and interfaces.
Source code files use the .java extension.
75. What is the
relationship between the Canvas class and the Graphics class?
A Canvas object provides access
to a Graphics object via its paint() method.
76. What are the
high-level thread states?
The high-level thread states are
ready, running, waiting, and dead.
77. What value
does read() return when it has reached the end of a file?
The read() method returns -1 when
it has reached the end of a file.
78. Can a Byte
object be cast to a double value?
No, an object cannot be cast to a
primitive value.
79. What is the
difference between a static and a non-static inner class?
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.
80. What is the
difference between the String and StringBuffer classes?
String objects are constants.
StringBuffer objects are not.
81. If a
variable is declared as private, where may the variable be accessed?
A private variable may only be
accessed within the class in which it is declared.
82. What is an
object's lock and which object's have locks?
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.
83. What is the
Dictionary class?
The Dictionary class provides the
capability to store key-value pairs.
84. How are the
elements of a BorderLayout organized?
The elements of a BorderLayout
are organized at the borders (North, South, East, and West) and the center
of a container.
85. What is the
% operator?
It is referred to as the modulo
or remainder operator. It returns the remainder of dividing the first operand
by the second operand.
86. When can an
object reference be cast to an interface reference?
An object reference be cast to an
interface reference when the object implements the referenced interface.
87. What is the
difference between a Window and a Frame?
The Frame class extends Window to
define a main application window that can have a menu bar.
88. Which class
is extended by all other classes?
The Object class is extended by
all other classes.
89. Can an
object be garbage collected while it is still reachable?
A reachable object cannot be
garbage collected. Only unreachable objects may be garbage collected..
90. Is the
ternary operator written x : y ? z or x ? y : z ?
It is written x ? y : z.
91. What is the
difference between the Font and FontMetrics classes?
The FontMetrics class is used to
define implementation-specific properties, such as ascent and descent, of a
Font object.
92. How is
rounding performed under integer division?
The fractional part of the result
is truncated. This is known as rounding toward zero.
93. What happens
when a thread cannot acquire a lock on an object?
If a thread attempts to execute a
synchronized method or synchronized statement and is unable to acquire
an object's lock, it enters the
waiting state until the lock becomes available.
94. What is the
difference between the Reader/Writer class hierarchy and the InputStream/
OutputStream
class hierarchy?
The Reader/Writer class hierarchy
is character-oriented, and the InputStream/OutputStream class hierarchy
is byte-oriented.
95. What classes
of exceptions may be caught by a catch clause?
A catch clause can catch any
exception that may be assigned to the Throwable type. This includes the Error
and Exception types.
96. If a class
is declared without any access modifiers, where may the class be accessed?
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.
97. What is the
SimpleTimeZone class?
The SimpleTimeZone class provides
support for a Gregorian calendar.
98. What is the
Map interface?
The Map interface replaces the
JDK 1.1 Dictionary class and is used associate keys with values.
99. Does a class
inherit the constructors of its superclass?
A class does not inherit
constructors from any of its superclasses.
100. For which
statements does it make sense to use a label?
The only statements for which it
makes sense to use a label are those statements that can enclose a break or
continue statement.
101. What is the
purpose of the System class?
The purpose of the System class
is to provide access to system resources.
102. Which
TextComponent method is used to set a TextComponent to the read-only state?
setEditable()
103. How are the
elements of a CardLayout organized?
The elements of a CardLayout are
stacked, one on top of the other, like a deck of cards.
104. Is
&&= a valid Java operator?
No, it is not.
105. Name the
eight primitive Java types.
The eight primitive types are
byte, char, short, int, long, float, double, and boolean.
106. Which class
should you use to obtain design information about an object?
The Class class is used to obtain
information about an object's design.
107. What is the
relationship between clipping and repainting?
When a window is repainted by the
AWT painting thread, it sets the clipping regions to the area of the
window that requires repainting.
108. Is
"abc" a primitive value?
The String literal
"abc" is not a primitive value. It is a String object.
109. What is the
relationship between an event-listener interface and an event-adapter class?
An event-listener interface
defines the methods that must be implemented by an event handler for a
particular kind of event. An
event adapter provides a default implementation of an event-listener interface.
110. What
restrictions are placed on the values of each case of a switch statement?
During compilation, the values of
each case of a switch statement must evaluate to a value that can be
promoted to an int value.
111. What
modifiers may be used with an interface declaration?
An interface may be declared as
public or abstract.
112. Is a class
a subclass of itself?
A class is a subclass of itself.
113. What is the
highest-level event class of the event-delegation model?
The java.util.EventObject class
is the highest-level class in the event-delegation class hierarchy.
114. What event
results from the clicking of a button?
The ActionEvent event is
generated as the result of the clicking of a button.
115. How can a
GUI component handle its own events?
A component can handle its own
events by implementing the required event-listener interface and adding
itself as its own event listener.
116. What is the
difference between a while statement and a do statement?
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.
117. How are the
elements of a GridBagLayout organized?
The elements of a GridBagLayout
are organized according to a grid. However, the elements are of different
sizes and may occupy more than
one row or column of the grid. In addition, the rows and columns may
have different sizes.
118. What
advantage do Java's layout managers provide over traditional windowing systems?
Java uses layout managers to lay
out components in a consistent manner across all windowing platforms.
Since Java's layout managers
aren't tied to absolute sizing and positioning, they are able to accomodate
platform-specific differences
among windowing systems.
119. What is the
Collection interface?
The Collection interface provides
support for the implementation of a mathematical bag - an unordered
collection of objects that may
contain duplicates.
120. What
modifiers can be used with a local inner class?
A local inner class may be final
or abstract.
121. What is the
difference between static and non-static variables?
A static variable is associated
with the class as a whole rather than with specific instances of a class.
Nonstatic
variables take on unique values
with each object instance.
122. What is the
difference between the paint() and repaint() methods?
The paint() method supports
painting via a Graphics object. The repaint() method is used to cause paint()
to
be invoked by the AWT painting
thread.
123. What is the
purpose of the File class?
The File class is used to create
objects that provide access to the files and directories of a local file
system.
124. Can an
exception be rethrown?
Yes, an exception can be
rethrown.
125. Which Math
method is used to calculate the absolute value of a number?
The abs() method is used to
calculate absolute values.
126. How does
multithreading take place on a computer with a single CPU?
The operating system's task
scheduler allocates execution time to multiple tasks. By quickly switching
between executing tasks, it
creates the impression that tasks execute sequentially.
127. When does
the compiler supply a default constructor for a class?
The compiler supplies a default
constructor for a class if no other constructors are provided.
128. When is the
finally clause of a try-catch-finally statement executed?
The finally clause of the
try-catch-finally statement is always executed unless the thread of execution
terminates or an exception occurs
within the execution of the finally clause.
129. Which class
is the immediate superclass of the Container class?
Component
130. If a method
is declared as protected, where may the method be accessed?
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.
131. How can the
Checkbox class be used to create a radio button?
By associating Checkbox objects
with a CheckboxGroup.
132. Which
non-Unicode letter characters may be used as the first character of an
identifier?
The non-Unicode letter characters
$ and _ may appear as the first character of an identifier
133. What
restrictions are placed on method overloading?
Two methods may not have the same
name and argument list but different return types.
134. What
happens when you invoke a thread's interrupt method while it is sleeping or
waiting?
When a task's interrupt() method
is executed, the task enters the ready state. The next time the task enters
the running state, an
InterruptedException is thrown.
135. What is
casting?
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.
136. What is the
return type of a program's main() method?
A program's main() method has a
void return type.
137. Name four
Container classes.
Window, Frame, Dialog,
FileDialog, Panel, Applet, or ScrollPane
138. What is the
difference between a Choice and a List?
A Choice is displayed in a
compact form that requires you to pull it down to see the list of available
choices. Only one item may be
selected from a Choice. A List may be displayed in such a way that several
List items are visible. A List
supports the selection of one or more List items.
139. What class
of exceptions are generated by the Java run-time system?
The Java runtime system generates
RuntimeException and Error exceptions.
140. What class
allows you to read objects directly from a stream?
The ObjectInputStream class
supports the reading of objects from input streams.
141. What is the
difference between a field variable and a local variable?
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.
142. Under what
conditions is an object's finalize() method invoked by the garbage collector?
The garbage collector invokes an
object's finalize() method when it detects that the object has become
unreachable.
143. How are
this() and super() used with constructors?
this() is used to invoke a
constructor of the same class. super() is used to invoke a superclass
constructor.
144. What is the
relationship between a method's throws clause and the exceptions that can be
thrown during
the method's execution?
A method's throws clause must
declare any checked exceptions that are not caught within the body of the
method.
145. What is the
difference between the JDK 1.02 event model and the event-delegation model
introduced with
JDK 1.1?
The JDK 1.02 event model uses an
event inheritance or bubbling approach. In this model, components are
required to handle their own
events. If they do not handle a particular event, the event is inherited by (or
bubbled up to) the component's
container. The container then either handles the event or it is bubbled up to
its container and so on, until
the highest-level container has been tried.
In the event-delegation model,
specific objects are designated as event handlers for GUI components.
These objects implement
event-listener interfaces. The event-delegation model is more efficient than
the
event-inheritance model because
it eliminates the processing required to support the bubbling of unhandled
events.
146. How is it
possible for two String objects with identical values not to be equal under the
==
operator?
The == operator compares two
objects to determine if they are the same object in memory. It is possible for
two String objects to have the
same value, but located indifferent areas of memory.
147. Why are the
methods of the Math class static?
So they can be invoked as if they
are a mathematical code library.
148. What
Checkbox method allows you to tell if a Checkbox is checked?
getState()
149. What state
is a thread in when it is executing?
An executing thread is in the
running state.
150. What are
the legal operands of the instanceof operator?
The left operand is an object
reference or null value and the right operand is a class, interface, or array
type.
151. How are the
elements of a GridLayout organized?
The elements of a GridBad layout
are of equal size and are laid out using the squares of a grid.
152. What an I/O
filter?
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.
153. If an
object is garbage collected, can it become reachable again?
Once an object is garbage
collected, it ceases to exist. It can no longer become reachable again.
154. What is the
Set interface?
The Set interface provides
methods for accessing the elements of a finite mathematical set. Sets do not
allow duplicate elements.
155. What
classes of exceptions may be thrown by a throw statement?
A throw statement may throw any
expression that may be assigned to the Throwable type.
156. What are E
and PI?
E is the base of the natural
logarithm and PI is mathematical value pi.
157. Are true
and false keywords?
The values true and false are not
keywords.
158. What is a
void return type?
A void return type indicates that
a method does not return a value.
159. What is the
purpose of the enableEvents() method?
The enableEvents() method is used
to enable an event for a particular object. Normally, an event is enabled
when a listener is added to an
object for a particular event. The enableEvents() method is used by objects
that handle events by overriding
their event-dispatch methods.
160. What is the
difference between the File and RandomAccessFile classes?
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.
161. What
happens when you add a double value to a String?
The result is a String object.
162. What is
your platform's default character encoding?
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..
163. Which
package is always imported by default?
The java.lang package is always
imported by default.
164. What
interface must an object implement before it can be written to a stream as an
object?
An object must implement the
Serializable or Externalizable interface before it can be written to a stream
as
an object.
165. How are
this and super used?
this is used to refer to the
current object instance. super is used to refer to the variables and methods of
the
superclass of the current object
instance.
166. What is the
purpose of garbage collection?
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.
167. What is a
compilation unit?
A compilation unit is a Java
source code file.
168. What
interface is extended by AWT event listeners?
All AWT event listeners extend
the java.util.EventListener interface.
169. What
restrictions are placed on method overriding?
Overridden methods must have the
same name, argument list, and return type. The overriding method may
not limit the access of the
method it overrides. The overriding method may not throw any exceptions that
may not be thrown by the
overridden method.
170. How can a
dead thread be restarted?
A dead thread cannot be
restarted.
171. What
happens if an exception is not caught?
An uncaught exception results in
the uncaughtException() method of the thread's ThreadGroup being
invoked, which eventually results
in the termination of the program in which it is thrown.
172. What is a
layout manager?
A layout manager is an object
that is used to organize components in a container.
173. Which
arithmetic operations can result in the throwing of an ArithmeticException?
Integer / and % can result in the
throwing of an ArithmeticException.
174. What are
three ways in which a thread can enter the waiting state?
A thread can enter the waiting
state by invoking its sleep() method, by blocking on I/O, by unsuccessfully
attempting to acquire an object's
lock, or by invoking an object's wait() method. It can also enter the
waiting state by invoking its
(deprecated) suspend() method.
175. Can an
abstract class be final?
An abstract class may not be
declared as final.
176. What is the
ResourceBundle class?
The ResourceBundle class is used
to store locale-specific resources that can be loaded by a program to
tailor the program's appearance
to the particular locale in which it is being run.
177. What
happens if a try-catch-finally statement does not have a catch clause to handle
an
exception that
is thrown within the body of the try statement?
The exception propagates up to
the next higher level try-catch statement (if any) or results in the program's
termination.
178. What is
numeric promotion?
Numeric promotion is the
conversion of a smaller numeric type to a larger numeric type, so that integer
and
floating-point operations may
take place. In numerical promotion, byte, char, and short values are
converted to int values. The int
values are also converted to long values, if necessary. The long and float
values are converted to double
values, as required.
179. What is the
difference between a Scrollbar and a ScrollPane?
A Scrollbar is a Component, but
not a Container. A ScrollPane is a Container. A ScrollPane handles its
own events and performs its own
scrolling.
180. What is the
difference between a public and a non-public class?
A public class may be accessed
outside of its package. A non-public class may not be accessed outside of
its package.
181. To what
value is a variable of the boolean type automatically initialized?
The default value of the boolean
type is false.
182. Can try
statements be nested?
Try statements may be tested.
183. What is the
difference between the prefix and postfix forms of the ++ operator?
The prefix form performs the
increment operation and returns the value of the increment operation. The
postfix form returns the current
value all of the expression and then performs the increment operation on
that value.
184. What is the
purpose of a statement block?
A statement block is used to
organize a sequence of statements as a single statement group.
185. What is a
Java package and how is it used?
A Java package is a naming
context for classes and interfaces. A package is used to create a separate name
space for groups of classes and
interfaces. Packages are also used to organize related classes and interfaces
into a single API unit and to
control accessibility to these classes and interfaces.
186. What
modifiers may be used with a top-level class?
A top-level class may be public,
abstract, or final.
187. What are
the Object and Class classes used for?
The Object class is the
highest-level class in the Java class hierarchy. The Class class is used to
represent
the classes and interfaces that
are loaded by a Java program.
188. How does a
try statement determine which catch clause should be used to handle an
exception?
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 exception
is executed. The remaining catch
clauses are ignored.
189. Can an
unreachable object become reachable again?
An unreachable object may become
reachable again. This can happen when the object's finalize() method is
invoked and the object performs
an operation which causes it to become accessible to reachable objects.
190. When is an
object subject to garbage collection?
An object is subject to garbage
collection when it becomes unreachable to the program in which it is used.
191. What method
must be implemented by all threads?
All tasks must implement the
run() method, whether they are a subclass of Thread or implement the
Runnable interface.
192. What
methods are used to get and set the text label displayed by a Button object?
getLabel() and setLabel()
193. Which
Component subclass is used for drawing and painting?
Canvas
194. What are
synchronized methods and synchronized statements?
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.
195. What are
the two basic ways in which classes that can be run as threads may be defined?
A thread class may be declared as
a subclass of Thread, or it may implement the Runnable interface.
196. What are
the problems faced by Java programmers who don't use layout managers?
Without layout managers, Java
programmers are faced with determining how their GUI will be displayed
across multiple windowing systems
and finding a common sizing and positioning that will work within the
constraints imposed by each
windowing system.
197. What is the
difference between an if statement and a switch statement?
The if statement is used to
select among two alternatives. It uses a boolean expression to decide which
alternative should be executed.
The switch statement is used to select among multiple alternatives. It uses
an int expression to determine
which alternative should be executed.
198. What is the
List interface?
The List interface provides
support for ordered collections of objects.
Most frequent
questions
0) Q: Java and
C++
A: Some of the similarities and
differences are in the table:
Features Java C/C++
Pointer No Yes
Operator Overload No Yes
Typedef, Define,
Preprocessors No Yes
Structures, Unions No Yes
Enums No Yes
Functions No (only methods within
classes) Yes
Goto statement No Yes
Automatic CoercionsNo(types
should be converted explicitly) Yes
Global Variables No. Variable is
part of a class Yes
Templates No Yes
Private, Protected, Public
Inheritance No Yes
Default parameters No Yes
Garbage Collection Yes No
Multi-thread support Yes No
Multiple Inheritance
Yes. Supports only interface
inheritance and not implementation inheritance!
Yes
Exception Handling
Yes. try/catch must be defined if
the function declares that it may throw an exception.
Yes. You may not include the
try/catch even if the function
throws an exception.
Function Overload Yes Yes
Internationalization Yes Yes
Include of other Objects #import
#include
Comments "//","/*
*/,/** */ "//","/* */"
1) Q: What is
the purpose of the toolkit in the Abstract Window Toolkit (AWT)? How does AWT
work ?
A: The AWT toolkit is an
interface between the abstract window layer and a specific windowing
implementation.
2) Q: What is
layout manager ? How does it work ?
A: A layout manager is an object
that positions and resizes the components in a Container according to
some algorithm; for example, the
FlowLayout layout manager lays out components from left to right until it
runs out of room and then
continues laying out components below that row.
3) Q: Advantages
and disadvantages of layout manager ?
4) Q: Compare
SWING components to standard AWT.
A: Swing is an extension of, and
not a replacement for the AWT. There is some overlap between AWT and
Swing (for example a Swing
JButton component might be viewed as an improved functional replacement
for an AWT Button component.) One
of the advantages of Swing components is that because the
components are not rendered on
the screen by the operating system, the look and feel of a component does
not change as the application or
applet is executed on different platforms running under different operating
systems. Furthermore, it is
possible to cause Swing components to mimic the look and feel of a specific
platform no matter what platform
the program is running on. This is known as pluggable look and feel.
Swing components support the JDK
1.1
Delegation Event Model. From an
event handling viewpoint, Swing components operate the same as
AWT components (except that Swing
provides a number of new event types). Many Swing components
don't have an AWT counterpart. A
number of new and exciting components are included in the Swing
library that don't exist in the
AWT (tooltips, progress bars, trees, etc.)
5) Q: What is
Java Beans ?
A: According to JavaSoft, "A
Java Bean is a reusable software component that can be manipulated visually
in a builder tool."
6) Q: What you know
about Corba implementation in Java ?
A: Java 1.2 promises full CORBA
IDL support.
7) Q: What do
you know about networking support in Java ?
A: Java supports
"low-level" and "high-level" classes. "Low-level"
classes provide support for socket
programming: Socket,
DatagramSocket, and ServerSocket classes. "High-level" classes
provide "Web
programming": URL,
URLEncoder, and URLConnection classes. Networking programming classes ease
the programming of network
applications, but do not substitute your knowledge of networking. Java
networking like anything else in
Java is platform-independent.
8) Q: What is it
object serialization ?
A: Serialization is a way to
convert objects (including complex data structures such as lists and
trees) into a stream of bytes.
9) Q: How to
make application thread-safe ?
A: You should use the word
synchronized to mark the critical section of code. You may also use other
methods of thread synchronization
(see wait(), notify(), notifyAll() etc.
10) Q: What is
it reflection (introspection) ? Why is reflection possible in the Java
language?
A: Reflection (introspection) is
querying a class about its properties, and operating on methods and
fields by the name for a given
object instance. Reflection is possible in the Java language because of late
binding.
11) Q: Why are
Java ARchive (JAR) files important?
A: JAR files bundle .class files
and optimize applet downloads.
Following answer
may not be correct
12) Describe
what happens when an object is created in Java
Several things happen in a
particular order to ensure the object is constructed properly:
1. Memory is allocated from heap
to hold all instance variables and implementation-specific data of the
object and its superclasses.
Implemenation-specific data includes pointers to class and method data.
2. The instance variables of the
objects are initialized to their default values.
3. The constructor for the most
derived class is invoked. The first thing a constructor does is call the
consctructor for its
superclasses. This process continues until the constrcutor for java.lang.Object
is called,
as java.lang.Object is the base
class for all objects in java.
4. Before the body of the
constructor is executed, all instance variable initializers and initialization
blocks
are executed. Then the body of
the constructor is executed. Thus, the constructor for the base class
completes first and constructor
for the most derived class completes last.
13) In Java, You
can create a String object as below : String str = "abc"; &
String str = new
String("abc");
Why cant a button object be
created as : Button bt = "abc" Why is it compulsory to create a
button object
as: Button bt = new
Button("abc"); Why this is not compulsory in String's case.
The main reason you cannot create
a button by
Button bt1= "abc";
is because "abc" is a
literal string (something slightly different than a String object, by-the-way)
and bt1 is
a Button object. That simple. The
only object in Java that can be assigned a literal String is java.lang.String.
Important to not that you are NOT
calling a java.lang.String constuctor when you type String s = "abc";
For example
String x = "abc";
String y = "abc";
refer to the same object. While
String x1 = new
String("abc");
String x2 = new
String("abc");
refer to two different objects.
14) What are the
main differences between Java and C++?
Everything is an object in Java(
Single root hierarchy as everything gets derived from java.lang.Object)
Java does not have all the
complicated aspects of C++ ( For ex: Pointers, templates, unions, operator
overloading, structures etc..)
The Java language promoters
initially said "No pointers!", but when many programmers questioned
how
you can work without pointers,
the promoters began saying "Restricted pointers." You can make up
your
mind whether it’s really a
pointer or not. In any event, there’s no pointer arithmetic.
There are no destructors in Java.
(automatic garbage collection)
Java does not support conditional
compile (#ifdef/#ifndef type).
Thread support is built into java
but not in C++.
Java does not support default
arguments. There’s no scope resolution operator :: in Java. Java uses the
dot for everything, but can get
away with it since you can define elements only within a class. Even the
method definitions must always
occur within a class, so there is no need for scope
resolution there either.
There’s no "goto "
statement in Java.
Java doesn’t provide multiple
inheritance (MI), at least not in the same sense that C++ does.
Exception handling in Java is
different because there are no destructors.
Java has method overloading, but
no operator overloading. The String class does use the + and +=
operators to concatenate strings
and String expressions use automatic type conversion, but that’s a special
built-in case.
Java is interpreted for the most
part and hence platform independent.
15) What are
interfaces?
Interfaces provide more
sophisticated ways to organize and control the objects in your system.
The interface keyword takes the
abstract concept one step further. You could think of it as a “pure” abstract
class. It allows the creator to
establish the form for a class: method names, argument lists, and return
types, but no method bodies. An
interface can also contain fields, but The interface keyword takes the
abstract concept one step
further. You could think of it as a “pure” abstract class. It allows the
creator to
establish the form for a class:
method names, argument lists, and return types, but no method bodies.
An interface can also contain
fields, but
An interface says: “This is what
all classes that implement this particular interface will look like.” Thus,
any code that uses a particular
interface knows what methods might be called for that interface, and that’s
all. So the interface is used to
establish a “protocol” between classes. (Some object-oriented programming
languages have a keyword called
protocolto do the same thing.)
15) How can you
achieve Multiple Inheritance in Java?
Java's interface mechanism can be
used to implement multiple inheritance, with one important difference
from c++ way of doing MI: the
inherited interfaces must be abstract. This obviates the need to choose
between different
implementations, as with interfaces there are no implementations.
16) What is the
difference between StringBuffer and String class?
A string buffer implements a
mutable sequence of characters. A string buffer is like a String, but can be
modified. At any point in time it
contains some particular sequence of characters, but the length and content
of the sequence can be changed
through certain method calls.
The String class represents
character strings. All string literals in Java programs, such as
"abc" are constant
and implemented as instances of
this class; their values cannot be changed after they are created.
17) Describe, in
general, how java's garbage collector works?
The Java runtime environment
deletes objects when it determines that they are no longer being used. This
process is known as garbage
collection.
The Java runtime environment
supports a garbage collector that periodically frees the memory used by
objects that are no longer
needed. The Java garbage collector is a mark-sweep garbage collector that scans
Java's dynamic memory areas for
objects, marking those that are referenced. After all possible paths to
objects are investigated, those
objects that are not marked (i.e. are not referenced) are known to be garbage
and are collected.
18) What's the
difference between == and equals method?
The equals method can be
considered to perform a deep comparison of the value of an object, whereas the
== operator performs a shallow
comparison.
The equals() method compares the
characters inside a string object. == operator compares two object
references to check whether they
refer to the same instances or not.
19) What are
abstract classes, abstract methods?
Simply speaking a class or a
method qualified with "abstract" keyword is an abstract class or
abstract
method.
You create an abstract class when
you want to manipulate a set of classes through a common interface. All
derived-class methods that match
the signature of the base-class declaration will be called using the
dynamic binding mechanism.
An abstract method is an
incomplete method. It has only a declaration and no method body. Here is the
syntax for an abstract method
declaration: abstract void f();
20) How can you
force all derived classes to implement a method present in the base class?
Creating and implementing an
interface would be the best way for this situation. Just create an interface
with empty methods which forces a
programmer to implement all the methods present under it.
Another way of achieving this
task is to declare a class as abstract with all its methods abstract.
21) What is the
difference between an Applet and an Application?
1. Applets can be embedded in
HTML pages and downloaded over the Internet whereas Applications have
no special support in HTML for
embedding or downloading.
2. Applets can only be executed
inside a java compatible container, such as a browser or appletviewer
whereas Applications are executed
at command line by java.exe or jview.exe.
3. Applets execute under strict
security limitations that disallow certain operations(sandbox model security)
whereas Applications have no
inherent security restrictions.
4. Applets don't have the main()
method as in applications. Instead they operate on an entirely different
mechanism where they are
initialized by init(),started by start(),stopped by stop() or destroyed by
destroy().
22) Java says
"write once, run anywhere". What are some ways this isn't quite true?
Any time you use system calls
specific to one operating system and do not create alternative calls for
another operating system, your
program will not function correctly.
Solaris systems and Intel systems
order the bits of an integer differently. (You may have heard of little
endian vs. big endian)
If your code uses bit shifting,
or other binary operators, they will not work on systems that have opposide
endianism.
23) Describe
java's security model.
Java's security model is one of
the most interesting and unique aspects of the language. For the most part
it's broken into two pieces: the
user adjustable security manager that checks various API operations like file
access, and the byte code
verifier that asserts the validity of compiled byte code.
public abstract class
SecurityManager java.lang.SecurityManager is an abstract class which different
applications subclass to
implement a particular security policy. It allows an application to determine
whether or not a particular
operation will generate a security exception.
24) What is the
difference between a Vector and an Array. Discuss the advantages and
disadvantages
of both?
The vector container class generalizes
the concept of an ordinary C array. Like an array, a vector is an
indexed data structure, with
index values that range from 0 to one less than the number of elements
contained in the structure. Also
like an array, values are most commonly assigned to and extracted from the
vector using the subscript
operator. However, the vector differs from an array in the following important
respects:
The size of the vector can change
dynamically. New elements can be inserted on to the end of a vector, or
into the middle. It is important
to note, however, that while these abilities are provided, insertion into the
middle of a vector is not as
efficient as insertion into the middle of a list.
A vector has more
"self-knowledge" than an ordinary array. In particular, a vector can
be queried about its
size, about the number of
elements it can potentially hold (which may be different from its current
size),
and so on.
A vector can only hold references
to objects and not primitive types.
Vector Implementaions are usually
slower then array because of all the functionality that comes with them.
As implemented in Java, vector is
a thread-safe class and hence all methods are synchronous methods,
which makes them considerably
slow.
25) How many
different types of JDBC drivers are present? Discuss them.
Type 1: JDBC-ODBC Bridge plus
ODBC Driver:
The first type of JDBC driver is
the JDBC-ODBC Bridge. It is a driver that provides JDBC access to
databases through ODBC drivers.
The ODBC driver must be configured on the client for the bridge to
work. This driver type is
commonly used for prototyping or when there is no JDBC driver available for a
particular DBMS.
Type 2: Native-API partly-Java
Driver:
The Native to API driver converts
JDBC commands to DBMS-specific native calls. This is much like the
restriction of Type 1 drivers.
The client must have some binary code loaded on its machine. These drivers
do have an advantage over Type 1
drivers because they interface directly with the database.
Type 3: JDBC-Net Pure Java
Driver:
The JDBC-Net drivers are a
three-tier solution. This type of driver translates JDBC calls into a
databaseindependent
network protocol that is sent to
a middleware server. This server then translates this DBMSindependent
protocol into a DBMS-specific
protocol, which is sent to a particular database. The results are
then routed back through the
middleware server and sent back to the client. This type of solution makes it
possible to implement a pure Java
client. It also makes it possible to swap databases without affecting the
client.
Type 4: Native-Protocol Pur Java
Driver
These are pure Java drivers that
communicate directly with the vendor's database. They do this by
converting JDBC commands directly
into the database engine's native protocol. This driver has no
additional translation or
middleware layer, which improves performance tremendously.
26) What does
the keyword "synchronize" mean in java. When do you use it? What are
the
disadvantages of
synchronization?
Synchronize is used when u want
to make ur methods thread safe. The disadvantage of synchronise is it
will end up in slowing down the
program. Also if not handled properly it will end up in dead lock.
1. Only use (and minimize it's
use)synchronization when writing multithreaded code as there is a speed (up
to five to six time slower,
depending on the execution time of the synchronized/non-synchronized method )
cost associated with its use.
2. In case of syncronized method
modifier, the byte code generated is the exact same as non-syncronized
method. The only difference is
that a flag called ACC_SYNCRONIZED property flag in method's
method_info structure is set if
the syncronized method modifier is present.
3. Also, syncronized keyword can
make the code larger in size if used in the body of the method as
bytecode for
monitorenter/monitorexit is generated in addition to any exception handling.
27) What are
native methods? How do you use them?
Native methods are methods that
are defined as public static methods within a java class, but whose
implementation is provided in
another programming language such as C.
28) What is RMI?
RMI stands for Remote Method
Invocation. Traditional approaches to executing code on other machines
across a network have been
confusing as well as tedious and error-prone to implement. The nicest way to
think about this problem is that
some object happens to live on another machine, and that you can send a
message to the remote object and
get a result as if the object lived on your local machine. This
simplification is exactly what
Java Remote Method Invocation (RMI) allows you to do.
29) What is
JDBC? Describe the steps needed to execute a SQL query using JDBC.
The JDBC is a pure Java API used
to execute SQL statements. It provides a set of classes and interfaces
that can be used by developers to
write database applications.
The steps needed to execute a SQL
query using JDBC:
1. Open a connection to the
database.
2. Execute a SQL statement.
3. Process th results.
4. Close the connection to the
database.
30) Access
specifiers: "public", "protected", "private",
nothing?
Public – any other class from any
package can instantiate and execute the classes and methods
Protected – only subclasses and
classes inside of the package can access the classes and methods
Private – the original class is
the only class allowed to executed the methods.
31) What does
the "final" keyword mean in front of a variable? A method? A class?
FINAL for a variable : value is
constant
FINAL for a method : cannot be
overridden
FINAL for a class : cannot be
derived
32) Does Java
have "goto"?
no
33) Why
"bytecode"? Can you reverse-engineer the code from bytecode?
34) What
synchronization constructs does Java provide? How do they work?
35) Are
constructors inherited? Can a subclass call the parent's class constructor?
When?
You cannot inherit a constructor.
That is, you cannot create a instance of a subclass using a constructor of
one of it's superclasses. One of
the main reasons is because you probably don't want to overide the
superclasses constructor, which
would be possible if they were inherited. By giving the developer the
ability to override a
superclasses constructor you would erode the encapsulation abilities of the
language.
36) Does Java
have destructors?
No garbage collector does the job
working in the background
37) What does
the "abstract" keyword mean in front of a method? A class?
Abstract keyword declares either
a method or a class. If a method has a abstract keyword in front of it,it is
called abstract method.Abstract
method hs no body.It has only arguments and return type.Abstract methods
act as placeholder methods that
are implemented in the subclasses.
Abstract classes can't be
instantiated.If a class is declared as abstract,no objects of that class can be
created.If a class contains any
abstract method it must be declared as abstract
38) Name four
methods every Java class will have.
public String toString();
public Object clone();
public boolean equals();
public int hashCode();
39) Given a text
file, input.txt, provide the statement required to open
this file with the appropriate
I/O stream to be able to read and process this file.
40) Discuss the
differences between creating a new class, extending a class and implementing an
interface; and when each
would be appropriate.
*Creating a new class is simply
creating a class with no extensions and no
implementations. The signature is
as follows
public class MyClass()
{
}
*Extending a class is when you
want to use the functionality of another class or
classes. The extended class
inherits all of the functionality of the previous class. An
example of this when you create
your own applet class and extend from
java.applet.Applet. This gives
you all of the functionality of the java.applet.Applet class.
The signature would look like
this
public class MyClass extends
MyBaseClass
{
}
*Implementing an interface simply
forces you to use the methods of the interface
implemented. This gives you two
advantages. This forces you to follow a standard
(forces you to use certain
methods) and in doing so gives you a channel for
polymorphism. This isn’t the only
way you can do polymorphism but this is one of the
ways.
public class Fish implements
Animal
{
}
40) What's the
difference between the == operator and the equals() method? What test does
Object.equals() use, and why?
The == operator would be used, in
an object sense, to see if the two objects were
actually the same object. This
operator looks at the actually memory address to see if it
actually the same object. The
equals() method is used to compare the values of the
object respectively. This is used
in a higher level to see if the object values are equal.
Of course the the equals() method
would be overloaded in a meaningful way for
whatever object that you were
working with.
41) why do you
create interfaces, and when MUST you use one.
You would create interfaces when
you have two or more functionalities talking to each other. Doing it this
way help you in creating a
protocol between the parties involved.
42) What is the
difference between instanceof and isInstance?
instanceof is used to check to
see if an object can be cast into a specified type without throwing a cast
class
exception.
isInstance()
Determines if the specified
Object is assignment-compatible with the object represented
by this Class. This method is the
dynamic equivalent of the Java language instanceof
operator. The method returns true
if the specified Object argument is non-null and can
be cast to the reference type
represented by this Class object without raising a
ClassCastException. It returns
false otherwise.
43) How many
methods do u implement if implement the Serializable Interface?
The Serializable interface is
just a "marker" interface, with no methods of its own to implement.
Are there any other 'marker'
interfaces?
java.rmi.Remote
java.util.EventListener
44) *What are
the advantages of developing an n-tiered system?
45) *Why is it
often difficult to separate the business layer from the data access layer?
46) . Diff
between ArrayList and Vector
47) Variable
shadowing with example
1. What is the diffrence between
an Abstract class and Interface ?
2. What is user defined exception
?
3. What do you know about the
garbate collector ?
4. What is the difference between
C++ & Java ?
5. Explain RMI Architecture?
6. How do you communicate in
between Applets & Servlets ?
7. What is the use of Servlets ?
8. What is JDBC? How do you
connect to the Database ?
9. In an HTML form I have a
Button which makes us to open another page in 15 seconds. How will do you
that ?
10. What is the difference
between Process and Threads ?
11. What is the difference
between RMI & Corba ?
12. What are the services in RMI
?
13. How will you initialize an
Applet ?
14. What is the order of method
invocation in an Applet ?
15. When is update method called
?
16. How will you pass values from
HTML page to the Servlet ?
17. Have you ever used HashTable
and Dictionary ?
18. How will you communicate
between two Applets ?
19. What are statements in JAVA ?
20. What is JAR file ?
21. What is JNI ?
22. What is the base class for
all swing components ?
23. What is JFC ?
24. What is Difference between
AWT and Swing ?
25. Considering notepad/IE or any
other thing as process, What > will happen if you start notepad or IE 3
times? Where 3 processes are
started or 3 threads are started ?
26. How does thread
synchronization occurs inside a monitor ?
27. How will you call an Applet
using a Java Script function ?
28. Is there any tag in HTML to
upload and download files ?
29. Why do you Canvas ?
30. How can you push data from an
Applet to Servlet ?
31. What are 4 drivers available
in JDBC ?
32. How you can know about
drivers and database information ?
33. If you are truncated using
JDBC, How can you know ..that how much > > > data is truncated ?
34. And What situation , each of
the 4 drivers used ?
35. How will you perform
transaction using JDBC ?
36. In RMI, server object first
loaded into the memory and then the stub reference is sent to the client ? or
whether a stub reference is
directly sent to the client ?
37. Suppose server object is not
loaded into the memory, and theclient request for it , what will happen?
38. What is serialization ?
39. Can you load the server
object dynamically? If so, what are the major 3 steps involved in it ?
40. What is difference RMI
registry and OSAgent ?
41. To a server method, the
client wants to send a value 20, with this value exceeds to 20,. a message
should be sent to the client ?
What will you do for achieving for this ?
42. What are the benefits of
Swing over AWT ?
43. Where the CardLayout is used
?
44. What is the Layout for
ToolBar ?
45. What is the difference between
Grid and GridbagLayout ?
46. How will you add panel to a
Frame ?
47. What is the corresponding
Layout for Card in Swing ?
48. What is light weight
component ?
49. Can you run the product
development on all operating systems ?
50. What is the webserver used
for running the Servlets ?
51. What is Servlet API used for
conneting database ?
52. What is bean ? Where it can
be used ?
53. What is difference in between
Java Class and Bean ?
54. Can we send object using
Sockets ?
55. What is the RMI and Socket ?
56. How to communicate 2 threads
each other ?
57. What are the files generated
after using IDL to Java Compilet ?
58. What is the protocol used by
server and client ?
59. Can I modify an object in
CORBA ?
60. What is the functionality
stubs and skeletons ?
61. What is the mapping mechanism
used by Java to identify IDL language ?
62. Diff between Application and
Applet ?
63. What is serializable
Interface ?
64. What is the difference
between CGI and Servlet ?
65. What is the use of Interface
?
66. Why Java is not fully
objective oriented ?
67. Why does not support multiple
Inheritance ?
68. What it the root class for
all Java classes ?
69. What is polymorphism ?
70. Suppose If we have variable '
I ' in run method, If I can create one or more thread each thread will
occupy a separate copy or same
variable will be shared ?
71. In servlets, we are having a
web page that is invoking servlets username and password ? which is cheks
in the database ? Suppose the
second page also If we want to verify the same information whether it will
connect to the database or it
will be used previous information?
72. What are virtual functions ?
73. Write down how will you
create a binary Tree ?
74. What are the traverses in
Binary Tree ?
75. Write a program for recursive
Traverse ?
76. What are session variable in
Servlets ?
77. What is client server
computing ?
78. What is Constructor and
Virtual function? Can we call Virtual funciton in a constructor ?
79. Why we use OOPS concepts?
What is its advantage ?
80. What is the middleware ? What
is the functionality of Webserver ?
81. Why Java is not 100 % pure
OOPS ? ( EcomServer )
82. When we will use an Interface
and Abstract class ?
83. What is an RMI?
84. How will you pass parameters
in RMI ? Why u serialize?
85. What is the exact difference
in between Unicast and Multicast object ? Where we will use ?
86. What is the main
functionality of the Remote Reference Layer ?
87. How do you download stubs
from a Remote place ?
88. What is the difference in
between C++ and Java ? can u explain in detail ?
89. I want to store more than 10
objects in a remote server ? Which methodology will follow ?
90. What is the main
functionality of the Prepared Statement ?
91. What is meant by static query
and dynamic query ?
92. What are the Normalization
Rules ? Define the Normalization ?
93. What is meant by Servelet?
What are the parameters of the service method ?
94. What is meant by Session ?
Tell me something about HTTPSession Class ?
95. How do you invoke a Servelt?
What is the difference in between doPost and doGet methods ?
96. What is the difference in
between the HTTPServlet and Generic Servlet ? Expalin their methods ? Tell
me their parameter names also ?
97. Have you used threads in
Servelet ?
98. Write a program on RMI and
JDBC using StoredProcedure ?
99. How do you sing an Applet ?
100. In a Container there are 5
components. I want to display the all the components names, how will you
do that one ?
101. Why there are some null
interface in java ? What does it mean ? Give me some null interfaces in
JAVA ?
102. Tell me the latest versions
in JAVA related areas ?
103. What is meant by class
loader ? How many types are there? When will we use them ?
104. How do you load an Image in
a Servlet ?
105. What is meant by flickering
?
106. What is meant by distributed
Application ? Why we are using that in our applications ?
107. What is the functionality of
the stub ?
108. Have you used any version
control ?
109. What is the latest version
of JDBC ? What are the new features are added in that ?
110. Explain 2 tier and 3 -tier
Architecture ?
111. What is the role of the
webserver ?
112. How have you done validation
of the fileds in your project ?
113. What is the main
difficulties that you are faced in your project ?
114. What is meant by cookies ?
Explain ?
Make sure you have a copy of your
resume in front of you. OK to have a cheat sheet or two - just don't let
anyone hear papers shuffling.
Know your OOA&D definitions,
such as polymorphism, inheritance, etc.
Know the difference between an
interface and an abstract class.
Know that Java does not support
multiple inheritance the way C++ does.
Know that you implement an
interface (can implement more than one).
Know that you extend an abstract
class (can only extend more than one).
Know about the access modifiers:
public/friendly(default)/protected/private. Be able to explain in one or
two sentences for each case. This
is where you can get tangled up in a phone conversation and confuse the
heck out of the interviewer and
yourself.
Know AWT Event Model - tough to
do over the phone - but you may get hit on a question.
Know the two ways to start a
thread - "extending Thread" or "implementing Runnable".
Know that the method is
"run" but to run a thread you use "start".
1. How can I
improve the performance of a java application, what are the java optimization
techniques.
That question is about as
meaningful as "how do you code stuff?" There's no one right answer,
and the
interviewer probably just wanted
to see if you knew *anything* about optimization. The answer is to go to
the Performance thread and read
the postings. If you search there for "books", you should find some
good
references which will get you
started. You should also search for "tools".
quote:
2. What should you do to ensure
that your applet works exactly the same way on both IE and netscape.
Short answers include: make sure
they use the same JVM, don't use complex GUIs, and most importantly
test to be certain! Personally, I'd question the
benefit of the applet and ask if could be done with JSPs.
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