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?
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.
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.
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
event-delegation 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.
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. Non-static 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.
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.
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 database-independent network protocol that is sent to a middleware
server. This server then translates this DBMS-independent 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 ?
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 ?
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 ?
