Wi-Fi, which stands for wireless fidelity, in a play on the older term Hi-Fi, is a wireless networking technology used across the globe. Wi-Fi refers to any system that uses the 802.11 standard, which was developed by the Institute of Electrical and Electronics Engineers (IEEE) and released in 1997. The term Wi-Fi, which is alternatively spelled WiFi, Wi-fi, Wifi, or wifi, was pushed by the Wi-Fi Alliance, a trade group that pioneered commercialization of the technology.
In a Wi-Fi network, computers with wifi network cards connect wirelessly to a wireless router. The router is connected to the Internet by means of a modem, typically a cable or DSL modem. Any user within 200 feet or so (about 61 meters) of the access point can then connect to the Internet, though for good transfer rates, distances of 100 feet (30.5 meters) or less are more common. Retailers also sell wireless signal boosters that extend the range of a wireless network.
Wifi networks can either be "open", such that anyone can use them, or "closed", in which case a password is needed. An area blanketed in wireless access is often called a wireless hotspot. There are efforts underway to turn entire cities, such as San Francisco, Portland, and Philadelphia, into big wireless hotspots. Many of these plans will offer free, ad-supported service or ad-free service for a small fee. San Francisco recently chose Google to supply it with a wireless network.
Wifi technology uses radio for communication, typically operating at a frequency of 2.4GHz. Electronics that are "WiFi Certified" are guaranteed to interoperate with each other regardless of brand. Wifi is technology designed to cater to the lightweight computing systems of the future, which are mobile and designed to consume minimal power. PDAs, laptops, and various accessories are designed to be wifi-compatible. There are even phones under development that would switch seamlessly from cellular networks to wifi networks without dropping a call.
Last week, Microsoft finally announced that there would be six editions of Windows 7, just like there were for Windows XP and Windows Vista. The company will release Windows 7 Starter (worldwide only via OEMs), Windows 7 Home Basic (only in emerging markets), Windows 7 Home Premium (retail and OEM), Windows 7 Professional (retail and OEM), Windows 7 Ultimate Edition (retail only during promotions and OEM), and Windows 7 Enterprise (volume licenses).
However, as part of its initiative to simplify the lineup, the software giant will only market Home Premium and Professional to average users. Most will be getting Windows 7 with their next purchase of a desktop, notebook, or netbook. (Speaking of netbooks, Microsoft also noted last week that all editions of Windows 7 will work on netbooks and it will be up to the OEM's discretion as to what editions they want to offer on each product.)
If you won't be going through an OEM, you'll either want to purchase a full retail copy of Windows 7, a cheaper upgrade edition, or the OEM version (usually the cheapest and best way). While Microsoft has not given details on pricing for any of the three, the company has agreed to offer upgrade options to both Windows XP and Windows Vista users, and they are worth outlining in detail. From Windows XP to Windows 7
Information here is still a bit murky because Microsoft has not specified which XP editions will be eligible. The good news is that the company has confirmed that users currently running Windows XP will be able to buy the cheaper upgrade option of Windows 7. However, they will only be able to perform a clean install. The hassle of backing up applications and user data will fall on the user; the upgrade process will not backup anything.
That may come as a shock to some, but Microsoft typically lets users purchase the cheaper upgrade option by owners of the last two releases of Windows (in this case XP and Vista) but the older of the two operating systems usually require a clean install. From Windows Vista to Windows 7
Microsoft will only allow the following upgrade paths to Vista users. For example, users who purchase an upgrade copy of Windows 7 Professional and have Vista Home Premium will only be able to perform a clean install. Here's the migration list:
* Windows Vista Home Premium to Windows 7 Home Premium * Windows Vista Business to Windows 7 Professional * Windows Vista Ultimate to Windows 7 Ultimate
If you are performing an upgrade installation from Windows Vista, the base language must match the target Windows 7 language, you must have about 9GB of free space for the installation, and the installation can only occur on the same partition that holds Windows Vista. Existing applications and user data will be automatically migrated to the new Windows 7 installation.
Clean installs will require about 16GB for the installation process. Unless the user chooses to repartition or format the current partition, Vista's files from C:\WINDOWS will be preserved under C:\WINDOWS.OLD, just as when upgrading from XP to Vista. Clean installs will also have to be performed when upgrading from a 32-bit version to a 64-bit version. Windows Anytime Upgrade (WAU)
Once you have some edition of Windows 7 on your system, whether you purchased it via an OEM or just upgraded from Windows XP or Windows Vista, you will be able to upgrade to a "more premium" version of Windows 7 by purchasing an upgrade key to unlock additional features, just as in with Vista. For example, you could start off with Windows Vista Home Premium, upgrade to Windows 7 Home Premium, and then later choose to upgrade to Windows 7 Professional.
As with Vista, the same DVD includes the various editions. Unlike with Vista, every edition of Windows 7 is a superset of the previous edition, so you will not lose any features when upgrading. Windows 7 for free and Ultimate Extras
Some users have argued that Microsoft should release Windows 7 for free to everyone, while others suggest that only Windows Vista users should get Windows 7 for free. Finally, a third group says that Windows 7 should be the final Ultimate Extra that Microsoft gives out to Windows Vista Ultimate users. All three are unlikely scenarios, though I do have something to say about the last one.
Last week, Microsoft noted that there would be no Ultimate Extras in Windows 7 Ultimate. Currently, if you upgrade Vista Ultimate to the Windows 7 Ultimate beta, your Ultimate Extras disappear. When I asked Microsoft if this was the expected behavior, I only got an "it's still in beta" response. In terms of the fate of Ultimate Extras on Vista, a spokesman told me the software giant still hasn't decided whether Microsoft Tinker was going to be the last Ultimate Extra that the company releases.
Assuming that Windows 7 will not end up an Ultimate Extra for Vista, the only way to get Windows 7 for free will be to buy a Vista computer after July 1. In other words, if you purchase a computer with Vista preloaded on it, from July 1, 2009 through January 31, 2010 (OEMs can choose to have an even shorter time frame within the one Microsoft gives), you will have the option to upgrade to Windows 7 for free when it becomes available.
According to a draft of the Windows 7 Technical Guarantee Program that Tech ARP acquired, the January 31 date may still change, depending on when Windows 7 is released.
As you can see, Microsoft is offering many options for moving to Windows 7 on the consumer side. But if the upgrade won't be free, what will it cost? There's still no word on pricing, but Microsoft is certainly aware of the state of the economy; let's hope the software giant doesn't lose its business sense at a time like this.
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.
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.
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 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 intialization 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.
I am Vijay Ganesh. I would like to share the interview questions to who is willing to crack the interviews. Here i am going to post some of the most asked interview questions.
