learn java programming step by step

learn java programming step by step

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JAVA

CONNECT PRINTER

CONNECT PRINTER 

Sharing the Printer

Step 1

Open the "Start" menu on the computer directly connected to the printer and click "Control Panel," "Printers and Other Hardware" and then "Printers and Faxes."

Step 2

Right-click on the printer's icon and click "Sharing." If the computer has multiple printers, pick the correct model.

Step 3

Click the "Sharing" tab and press "Share As." Type in any name for the printer to identify it to other users on the network.

Step 4

Push "Additional Drivers" if any computers on the network use a different operating system than the computer attached to the printer. Follow the prompts to pick the extra drivers to install. If you're missing any drivers for another operating system, users printing from that system will have to install them on their end instead.

Step 5

Click "Ok," or "Close" if you installed additional drivers.

Adding the Printer

Step 1

Open the "Start" menu on another computer on the network and click "Control Panel," "Printers and Other Hardware" and then "Printers and Faxes."

Step 2

Click "Add a Printer" under "Printer Tasks" and press "Next" to start the Add Printer Wizard.

Step 3

Select the option labeled "A network printer, or a printer attached to another computer" and click "Next."

Step 4

Click "Connect to this printer" and type in the location of the printer in the format "\\Computer\Printer," where "Computer" is the network name of the computer attached to the printer, and "Printer" is the name given to the printer during sharing. You can also browse the network to locate the printer instead.

Step 5

Press "Next" and wait while the setup finishes. After it completes, close the window and print a test from the shared printer to ensure it works.

TYPE OF ATTACKS

Viruses

 A virus is a destructive program that infects systems by replicating itself and spreading across the network. Viruses can easily hide within a system by attaching themselves to other files or programs because they are small. It is difficult to trace a virus after it has spread across a network. Viruses either destroy data or change the functionality of the software applications on a computer. Virus attacks are one of the main areas that need to be considered while planning for the security of the networking infrastructure within an organization.

Worms 

A worm is a self-replicating program that uses the network and security gaps for its replication. It scans the network for a computer with a specific security gap. The worm copies itself to a computer by using the security gap and starts replicating itself into the newly infected computer. A worm also takes up the memory resources of a computer system on a network. In addition, a worm can travel across networks, and consumes the network bandwidth and system memory of the computers in the network.

Some of the differences between a virus and a worm are:

• A virus can replicate itself from one program to another on a single computer. However, a worm can replicate itself from one computer to another in a network.
•  A worm spreads faster than a virus. This is because a virus needs human intervention to spread from one computer to another unlike a worm. 

Trojan Horse

 Trojan Horse is a destructive program that masquerades as a useful program. Trojans do not replicate themselves like viruses. Users install Trojans thinking them to be legitimate programs. However, Trojans can contain viruses 

that destroy or corrupt the data and programs on the network. Trojans can also corrupt software applications. Like the name suggests, a Trojan can bring other viruses and worms with itself. A Trojan can be concealed within any software. Trojans can also be created by using existing utility programs. 

Man-in-the-Middle Attacks

 In the man-in-the-middle attack, a hacker can redirect the data being exchanged between two authorized entities to multiple unauthorized entities. In other words, before the authorized entities exchange data, a third party intercepts to monitor, capture, or control communication on a network. In this type of attack, the hacker acts as an authorized entity and captures the data meant for the authorized entity.

Denial-of-service Attacks 

A Denial-of-service (DoS) attack is a mechanism of making a computer or network resource, such as a Web server, unavailable to the intended users. Such attacks generally target sites or services hosted on Web servers, such as banks and credit card payment gateways. DoS attacks are based on the concept of network congestion or starvation of resources and aimed at disrupting network use for legitimate users. Resource starvation can be caused in many ways. Typical examples would include sending a large number of junk email messages or a large number of IP request packets to a mail server. Any intruder can cause network congestion by sending loads of junk data over the network. As a result, the target computers are inaccessible for some time because all routes to reach the computers are blocked. It can even cause the target computers to stop responding due to lack of resources, such as memory and disk space. A DoS attack can be executed from any IP packet sent over a network. The intruder’s identity is kept anonymous. Some of the commonly used methods to initiate DoS attacks are:

• SYN flood
•  Broadcast storm
•  Ping of death 
• Mail bomb 
• Spamming 

SYN Flood

 The SYN flood attack is primarily focused on the TCP protocol used by all the computers on the Internet. To understand how this attack occurs, you need to understand the SYN-ACK (three-way) handshake process

The steps in this process are: 

The first node requests communication by sending a packet with the sequence number and the SYN bit. The second node acknowledges the receipt of data and responds with an acknowledgement (ACK) that contains the sequence number, plus one increment in value, and its own sequence number (SYN-ACK). The first node responds, and the communication between the two nodes continues. 

Broadcast Storm 

In a broadcast storm , an intruder sends a large number of fake broadcast packets to all the computers on the network. As a result, each computer forwards these packets to the specified fake target address, increasing the amount of network traffic excessively. 

Ping of Death 

Ping of death is a technique that involves sending abnormally large ping packets to a specific computer. The target computer receives the ping command in fragments. On receiving the ping command, the computer tries to reassemble the fragments into a big packet. However, the size of the data packets is so large that they cannot fit into the computer’s buffer. As a result, these large-sized ICMP packets cause an overflow, which may cause the system to stop responding, reboot frequently, or the protocol will hang.

Mail Bomb 

The mail bomb is a simple and effective harassment tool. In a mail bomb attack, a message is sent repeatedly to the targeted recipient. This action can cause the recipient’s mail box to crash or spam by sending unauthorized mails by using the target’s Simple Mail Transfer Protocol (SMTP) gateway. Mail bombs can exist in the form of an email message that has huge files attached or is in the 

form of thousands of email messages. For example, some software programs generate thousands of email messages and dispatch them to a user’s mailbox, causing the mail server to stop responding or denying users resources.

 Spamming

 Spamming is an attempt to deliver an email message to someone who might otherwise not choose to receive it. The most common example is commercial advertising. Mail spamming engines are sold on the Internet, with thousands of email addresses adding to the explosive growth of junk mail.

Password-cracking 

On a typical computer network, all the users have fixed passwords until they decide to change it. When the password is typed in, the computer’s authentication kernel encrypts and translates it into a string of characters, and checks it against the long list of encrypted passwords. This list is in a password file stored on the computer. When the authentication module finds an identical string of characters paired with the user name, access to the system is permitted. If a hacker gains access to a copy of this file and runs a password-cracking program, the string of characters can be converted to the original password. A password-cracking program encrypts a long list of character strings, such as all the words in a dictionary, and checks it against the encrypted set of passwords. If the program finds even one match, an intruder can access the system. This type of attack does not require a high level of skill, and as a result, many password-cracking programs are available on the Internet.

Sniffing

 A sniffer is a hardware or software device that passively intercepts and copies all the network traffic on a system, a server, a router, or a firewall. Intruders can use stealth sniffers that are extremely dangerous to a network’s security because they are difficult to detect and can be self-installed almost anywhere. Most stealth sniffers are programmed to specifically detect and extract a copy of data containing a user name and a password. The attacker can then use a network utility or hacking software to capture the user name and password, and impersonate the user. The attacker gains access to the remote server with the help of captured credentials. 

Spoofing

 Spoofing is used to assume the identity of a trusted host to subvert security and attain trustful communication with a target host. IP spoofing is a form in which a network attacker breaches security and gains access by masquerading as a trusted host. 

Email Hacking

 Users often use email to communicate with other users. If email headers and content are sent in the plaintext format, hackers may read or alter the messages in transit. Hackers may also change the header to modify the sender name or redirect the message to another user. They may use a technique called packet replay to retransmit message packets over a network. Packet replay may cause serious security threats to programs on the network that require authentication sequences. A hacker may replay the packets containing authentication data to gain access to the resources of a computer system on a network.

security threats

 SECURITY THREATS

In context of computers, the term security refers to the protection of system resources from intentional or accidental disclosure, destruction, or modification. These resources include infrastructure, hardware, software applications, files and directories, the data stored in the database, and the data in transit.

 Different types of security threats, which can be:

• Network security
•  threats Attacks

Network Security Threats

Based on their sources, security threats can be broadly categorized into human threats and threats caused by natural calamities. 

Natural Calamities 

Security threats from natural calamities include damage caused to network systems due to floods, earthquakes, hurricanes, and fire. This may result in the loss of information, system downtime, or damage to hardware. For example, if the organizational premises of an organization are destroyed due to flood in the area, the computer resources will become unusable. The operations would stop and there is a possibility that critical data is lost. This may amount to huge losses to the organization. 

Human Threats

 Human threats include threats from the users of a computer system on a network or on the host machine. Human threats can be further categorized into intentional and unintentional threats. 

Intentional Threats

 Intentional threats include threats from the internal and external users of a computer system. The motive behind intentional attacks is to delete or alter important information, commit information theft, cause damage to 

the resources, commit fraud by impersonation, or disrupt the normal, day-to-day business activities of an organization. 

External users include hackers. A hacker is a person who breaks into a system on a network without owning the appropriate authorization. Hackers discover the vulnerabilities of a computer system on the network and exploit these weaknesses to gain control of the system. After taking control of the system, hackers can easily access confidential information and manipulate the resources of the system on a network. For example, a hacker can attack an e-commerce website and gain access to the credit card numbers provided by the users of this website. 

Unintentional Threats 

Unintentional threats are threats from ignorant users who perform certain tasks without knowing the impact of their actions. These threats are usually from employees who are not trained to use computer systems and are unaware of the security threats and vulnerabilities. For example, a data entry operator may key in erroneous data, which may affect the consistency of the data stored in a database. Another example is that of a programmer who may develop an erroneous application that may cause the system to stop responding

Different Types of Attacks

• Viruses Worms
•  Trojan horse
•  Man-in-the-middle attacks
•  Denial-of-service (DoS)
•  Password-cracking
•  Sniffing
•  Spoofing 
• Email hacking 

word

Introducing the Ribbon Panel Ribbon is a panel at the top of a Word document window. It comprises easily accessible commands required to work on a document. The Ribbon panel consists of the following eight basic tabs:


Home : This tab contains options that help you perform basic functions in a Word document, such as formatting and editing text.
Insert : This tab contains options that help you add different objects, such as pictures, tables, shapes, apps, media, and symbols in a document. You can insert these objects from your local PC or from various online sources. The online options include inserting images within the Office Clipart collection online, via a Bing search, or from your own SkyDrive.
Design : This tab makes it easier to use themes, styles, and other formatting features, such as the page background color, page border, or document watermark.
 Page Layout : This tab contains options that help you define page settings in a document. In addition, it contains options for controlling the position of text and graphics.
References : This tab contains options for citing sources of information and creating a bibliography. It also helps you select a style for formatting the citations and references in a document.
 Mailings : This tab contains the options related to a feature called mail merge. Mail merge helps you create and print letters and mailing labels.
Review : This tab contains various options that help you review and edit the contents of a document. View : This tab contains various options that help you view a document in different layouts.
Each tab is divided into several groups incorporating features designed to perform specific tasks during document creation. You can hide the Ribbon panel by double-clicking any
active tab.

HUB

HUB

A hub is a central network device used to connect multiple nodes to form a single network. It contains a number of ports to connect multiple computers. When a computer connected to a hub needs to communicate, it sends data packets to the hub. When a data packet arrives at the hub, it broadcasts the data packet to all devices in the network. The destined recipient whose Media Access Control (MAC) address is mentioned in the data packet receives it,
and all the other devices discard the data packet. The following figure shows a hub.

A Hub This method of transmitting a data packet is inefficient because all the nodes receive the data packet even if the data packet is not meant for them. In addition, when the data packets are on the network, the network cannot be used by other devices, which results in network traffic. This wastes network bandwidth. It also causes security problems because all the nodes can read the data packet sent by the hub. When two nodes simultaneously send the data packet to the hub, a collision occurs. When this collision occurs, the message becomes unreadable and the network must reset itself before delivering the data packet again. A hub can have 5, 8, 16, or more ports depending on its size. In addition, a hub contains a port, known as uplink port, which is used to connect with the next hub.

NOTE

A data packet is a basic unit of communication on a network. The data always travels in the form of data packets in a network.
A MAC address is a binary address unique to a single network. This address is 4 8 -bit long and is used to identify each node of a network uniquely.

WHAT IS NETWORK DEVICES?

WHAT IS NETWORK DEVICES?

Network Devices
In a small network, you can connect computers directly with the help of cables. However, in a large network, such as MAN, connecting computers with each other directly through cables is difficult. In addition, it may cause problems in managing the network. In such cases, you need hardware devices to set up a network. You can place these devices in a network and connect each node on the network with them. Various hardware devices are required to establish a network connection. These devices are collectively known as communication devices. The commonly used communication devices in a network are:

• Hub
•  Switch
•  Router 
• Bridge
•  Gateway 
• Modem

Wireless Network

Wireless Network

Mobile communication and connectivity over networks have become indispensable with the increased use of laptops, cell phones, and other mobile communication devices. For an individual who is located away from the main office network, physical connectivity with the office network is not always possible. In these situations, wireless connectivity proves useful. The advantage of the wireless technology is that it helps connect distant networks without needing to physically set up cables between the destination and source points. A wireless setup uses the atmosphere to transmit and receive signals in the form of electro-magnetic waves using an antenna. The electro-magnetic waves can be transmitted through different types of wireless transmission carriers, which include the following:

1. Radio
2.  Microwave
3.  Bluetooth

Radio

 Radio transmissions operate on radio waves. Radio waves are electro-magnetic waves used for transmitting audio signals, video signals, and data. Radio waves are less expensive than other wireless media and are relatively easy to install. However, they require skilled personnel to implement them. Radio waves are only limited to low transmission capacities, from 1 Mbps to 10 Mbps. If low- power devices are used, they may also suffer from weakening and distortion. However, with high power devices, the attenuation rate is much lower. The limitation of radio waves is that they are susceptible to EMI and eavesdropping, which allow outsiders to tap into an ongoing transmission. As a result, they are not recommended for confidential information exchanges. The following figure shows a radio transmission tower.

Microwave

 Microwave transmissions send data over a higher bandwidth than radio transmissions. Although microwaves support higher bandwidths and longer distances, they are more expensive than radio waves. The greater the range of transmission, the more expensive is the microwave transmissions. Microwave transmissions setups are difficult to install as they require extreme precision. In addition, their transmission is affected by atmospheric conditions, such as rain and fog. Similar to radio waves, microwaves are also susceptible to EMI and eavesdropping. 

Bluetooth 

A Bluetooth is a network standard that defines how two Bluetooth-enabled devices transmit data using short-range radio waves. To establish communication between two Bluetooth devices, the devices must be within 10 meters of range. The data between Bluetooth devices is transferred at a maximum rate of 3 Mbps. A Bluetooth device contains a small chip that enables it to communicate with other Bluetooth-enabled devices. Some examples of Bluetooth-enabled devices are laptops, cell phones, digital cameras, microphones, and printers. When two computers share data through Bluetooth, the recipient computer has a choice of accepting or declining the data. The following figure shows the logo of Bluetooth.

Network Media

Network Media

The physical channel that connects network components, such as nodes and printers, is known as transmission medium or network medium. The transmission medium determines speed and connectivity of the network, the resulting overall performance of the network, and the investment required to set up the network. The two types of network media are:

Cables : 

Cables connect networks over short distances. Different types of cables that can be used to set up networks include twisted pair cables, coaxial cables, and fiber optic cables.

Wireless :

 Wireless transmission channel connect mobile computers, such as laptops and PDAs, over a network. Various types of wireless transmission media are radio wave and microwave media.

Based on the type of media in the network, you can form wired network or a wireless network.

Wired Network

Cables are conventional media that is used to set up wired networks. 

The following types of cables are available to set up a wired network:

• Twisted pair cable
•  Coaxial cable 
• Fiber optic cable
•  Twisted Pair Cable 

Twisted pair cables

 are the most widely used cables for setting up networks. A twisted pair cable uses copper wires, which are good conductors of electricity. However, when two copper wires are placed in close proximity, they interfere with each other’s transmission, resulting in EMI. This is known as crosstalk. In a twisted pair network cable, multiple pairs of wires are twisted around each other at regular intervals. The twists negate the electro- magnetic field and reduce network crosstalk . Twisted pair cables are easy to set up, economical, and widely available media for network transmission. However, this media cannot be used in areas where network security is critical or the network is close to electronically sensitive equipment that may prove to be a potential source of EMI. Twisted pair cables are of the following types:

1. Unshielded Twisted Pair (UTP) cables
2.  Shielded Twisted Pair (STP) cables

 Unshielded Twisted Pair Cables 

UTP cables are the most commonly used cabling media. This type of cable is generally used in telephone systems. UTP cables consist of a set of twisted pairs that are covered with a plastic jacket. However, this plastic jacket does not provide any protection against EMI. To ensure that data transmission is not disrupted due to EMI, UTPs are not installed in close proximity to electro-magnetic devices. Another problem related to these cables is the signals that the UTP cables carry undergo rapid attenuation. As a result, the recommended length of these cables is not more than 100 meters. 

Shielded Twisted Pair Cables 

STP cables consist of multiple twisted pairs surrounded by an insulator shield. This shield protects the copper-based core from EMI. This insulator shield, in turn, is covered with a plastic encasement.

STP cables are protected against EMI by two layers. As a result, they are less sensitive to EMI and interference. However, STP cable shielding should be grounded to prevent interference in the cable. In addition, as compared to UTP, STP cables offer higher transmission rates - from 16 Mbps to 155 Mbps. Despite high transmission rates, STP cables have a number of limitations. They are expensive and not as widely available as UTP and coaxial cables. STP cables are not implemented commonly on large networks because of their incompatibility with the normal telephone cabling. 

Coaxial cables, 

commonly referred to as coax cables, derive their name from their structure. The structure is designed in a way that the two conductors share a common axis. The structure of the coaxial cable consists of a center conductor responsible for transmitting data. The outer conductor or shield protects this center conductor from EMI, ensuring that data transmission is not disrupted. The insulator provides a uniform space between the two conductors. A plastic jacket covers the cable and protects it from damage.

Fiber Optic Cable

 Fiber optic cables are based on fiber optic technology, which uses light rays or laser rays instead of electricity to transmit data. This makes fiber optics a suitable carrier of data in areas that are prone to high levels of EMI or for long distance data transmissions, where electrical signals may be significantly distorted and degraded. The components of a fiber optic cable include light- conducting fiber, cladding, and insulator jacket. The cladding covers core fiber and prevents light from being reflected through the fiber and the insulating jacket. The outer covering (or the insulator jacket) is responsible for providing required strength and support to the core fiber as well as for protecting the core fiber from breakage or high temperature. The fiber optical cables can have single or multiple paths for light rays. Based on this, fiber optic cables can be differentiated into the following categories:

Single mode cables : 

These cables use single mode fiber, which provides a single path for light rays to pass through the cables. A single mode fiber is suitable for carrying data over long distances. The following figure shows a single mode cable.

Multimode cables :

 These cables use multimode fiber, which provide multiple paths for light rays to pass through. Light rays are unaffected by large distances or environment, the signals do not attenuate or suffer from EMI or other interferences. This makes multimode cables extremely safe and prevents outsiders from eavesdropping on an ongoing transmission.

IP

IP ADDRESS

An IP address is a unique number that identifies a resource in a network. The first part of the IP address identifies the network in which the host resides, and the second part identifies the host in the network. This can be explained in the context of the postal system. The postal address on a letter has the complete address of the receiver, including the house number, street name and number, city, and state. Using this address, the postal system identifies the exact house or office for delivering the letter.

1. Move the cursor to the bottom right of the screen to display the Charms bar, and then select Search . The apps page is displayed on the screen, with the Search pane on the right side.
2.  Select Settings in the Search pane , and then type Network and Sharing Center in the search box. The results are displayed in the Settings screen. 
3. Select the Network and Sharing Center tile from the results. The Network and Sharing Center window is displayed. 
4. Click the Change adapter settings link in the left pane. The Network Connections window is displayed. Right-click the active network adapter, and then select Properties . 

If the User Account Control dialog box is displayed, you need to provide the administrator credentials. If you already have the administrative rights, then you need to click the Yes button.
 5.Select the Internet Protocol Version (TCP/ IPv4) option under the This connection uses the following items section.
6. Click the Properties button. The Internet Protocol Version 4 (TCP/IPv4) Properties dialog box is displayed.
7.Ensure that the Use the following IP address option is selected.
8.Type the IP address provided by tech support in the IP address text box. Type the Subnet mask provided by tech support in the Subnet mask text box.
9.Subnet mask is used to define the network and host portion of an IP address.
10.Type the default gateway provided by your ISP in the Default gateway text box.
11.Ensure that the Use the following DNS server addresses option is selected.
12. Type the preferred DNS server provided by your ISP in the Preferred DNS server text box.
13.Click the OK button.
14.Click the Close button.

NOTE

Domain Name Server (DNS) address is used to define the servers that maintain the database, which maps IP addresses with the domain name of the servers, such as yahoo.com, and Universal Resource Locators (URLs) of websites, such as www.yahoo.com. DNS is used to perform one simple task of converting IP addresses to domain names that can be easily understood by everyone. It can be compared with the phone book. For example, if you know someone’s name but do not know his/her number, you can look up in the phone book to search for the number. DNS provides the similar service. For example, when you use the URL in a Web browser to visit a Web site, the computer uses the DNS service to retrieve the IP address of the site.

Network topology

. In a network based on the tree topology:

A child can only directly communicate with its parent and with no other node in the network. A parent can only directly communicate with its children and with its own parent. While sending a message from one node to another, the message must travel from the source node up the tree to the nearest common ancestor and then down the tree to the destination node.

 Hybrid topology

The hybrid topology is not a basic topology. However, it can be a combination of two or more basic topologies, such as bus, ring, star, mesh, or tree. For example, a star network can be connected to another bus network, which is further connected to a ring network. This new network, formed by two or more sub-networks of different
topologies, will be of a hybrid topology.

Network Topologies

Network Topologies

You can place the computers and other devices in a network in different physical layouts, termed as network topologies. The network topology is a schematic layout or map of the arrangement of nodes over a network. This layout also determines the manner in which information is exchanged within the network. The different types of network topologies that can be used to set up a network are:

• Bus
•  Star 
• Ring 
• Mesh 
• Tree
•  Hybrid

BUS

The bus topology connects all the nodes on a network to a main cable called bus. 

The star topology connects nodes over a network using a central control unit called the hub. The hub is a device that transmits information from one node to another. 

ring topology , each node in a network is connected with two adjacent nodes and, therefore, forms a circle. The ring topology connects the nodes on a network through a point- to-point connection. 

 in mesh topology , each node in a network is directly connected with every other node in the network. The mesh topology involves point-to-point connections between all the nodes on a network. 

Network Architecture

 Network Architecture

Computers and other devices connected on a network can interact with each other in many ways depending on the architecture of the network. The architecture of a network is a logical design that determines how devices in the network communicate. The commonly used architectures for computer networks are:

• The Client-server architecture 
• The Peer-to-peer architecture 
• The Hybrid architecture

The Client-server Architecture

On a network built using the client-server architecture, the devices communicate to other devices through a central computer referred to as a server. A server is a computer with high processing power, which provides services to other computers on the network. A client is a computer that accesses resources available on the network and those offered by a server. A server is connected to multiple client nodes. The client nodes may have relatively low or no processing capabilities of their own. The client computers send requests to the server for processing information.

The Peer-to-peer Architecture

On a network built using the peer-to-peer architecture, no specific distinction exists between a client and a server computer. In other words, any node can provide a service as well as send a request for a service from another node on the network. The peer-to-peer network architecture allows sharing of resources, data, and users. Each node on the network can have full control over the network resources. However, each user can only access resources for which access privileges have been assigned to the user. Peer-to-peer networks are also referred to as workgroups or P2P networks. 

The Hybrid architecture

A hybrid, in general, is a composition of different types of elements. In computer networks, the hybrid network architecture is not a basic architecture. However, it is a combination of the two basic network architectures, peer- to-peer and client-server. 

NETWORK

NETWORK

A network is a group of computers and other devices, such as a Personal Digital Assistant (PDA) or a printer, connected together with a medium, such as a cable. A network can be created to enable the devices communicate or share resources, such as a file or a printer. A network provides various features, such as:


Data sharing : You can access or share data stored on computers over a network spread across geographical locations.
 Resource sharing : You can share hardware peripheral devices, such as printers and scanners, over the network rather than investing in individual resources for each computer.

. Based on the size and coverage area, networks are categorized into following types:

• Personal Area Networks (PANs)
•  Local Area Networks (LANs) 
• Metropolitan Area Networks (MANs) 
• Wide Area Networks (WANs)

A PAN is a small network established for communication between different devices, such as laptops, computers, mobiles, and PDAs. The network extends to a range of 10 meters. The following figure shows a PAN.

A LAN connects computers in a room, the floors of a building, or a campus to share resources and exchange information extending up to a few kilometers. For example, when computers used at your home are connected together and share a printer, it forms a small LAN.The following figure shows a LAN.

MANs are relatively larger than LANs and extend across a city or a metropolitan. This is how they derive their name. A MAN is created by two or more LANs located at different locations in a city. For example, when the network of computers at different colleges of a university is connected together, it forms a MAN. The following figure shows a MAN.

WAN provides network connectivity spanning across large geographical areas, such as across states, countries, or the globe. A WAN may consist of two or more LANs and/or MANs. One of the most prominent examples of existing WANs is the Internet. The following figure shows a WAN that connects different large networks together.

window.alertin javascript

Using window.alert()

You can use an alert box to display data:

Example

<!DOCTYPE html>
<html>
<body>

<h1>My First Web Page</h1>
<p>My first paragraph.</p>

<script>
window.alert(5 + 6);
</script>

</body>
</html>

sotware in excel

FROM in EXCEL Using Visual Basic

 

FROM in EXCEL Using Visual Basic

CODING FOR SAVE BUTTON 

(excel From )

Private Sub CommandButton1_Click()

Dim rowcount As String

rowcount = Worksheets("sheet1").Range("A1").CurrentRegion.Rows.Count

With Range("a1")

.Offset(rowcount, 0).Value = Me.TextBox1.Value

End With

Dim rowcount2 As String

rowcount2 = Worksheets("sheet1").Range("b1").CurrentRegion.Rows.Count

With Range("b1")

.Offset(rowcount, 0).Value = Me.TextBox2.Value

End With

Dim rowcount3 As String

rowcount3 = Worksheets("sheet1").Range("c1").CurrentRegion.Rows.Count

With Range("c1")

.Offset(rowcount, 0).Value = Me.ComboBox1.Value

End With

Dim rowcount4 As String

rowcount4 = Worksheets("sheet1").Range("d1").CurrentRegion.Rows.Count

With Range("d1")

.Offset(rowcount, 0).Value = Me.TextBox3.Value

End With

Dim rowcount5 As String

rowcount5 = Worksheets("sheet1").Range("e1").CurrentRegion.Rows.Count

With Range("e1")

.Offset(rowcount, 0).Value = Me.TextBox4.Value

End With

Dim rowcount6 As String

rowcount6 = Worksheets("sheet1").Range("f1").CurrentRegion.Rows.Count

With Range("f1")

.Offset(rowcount, 0).Value = Me.TextBox5.Value

End With

If Me.TextBox1.Value = "" Then

MsgBox "Fill the Entry!", vbExclamation, "Warning"

Me.TextBox1.SetFocus

Exit Sub

End If

If Me.TextBox2.Value = "" Then

MsgBox "Fill the Entry!", vbExclamation, "Warning"

Me.TextBox2.SetFocus

Exit Sub

End If

If Me.TextBox3.Value = "" Then

MsgBox "Fill the Entry!", vbExclamation, "Warning"

Me.TextBox3.SetFocus

Exit Sub

End If

If Me.TextBox4.Value = "" Then

MsgBox "Fill the Entry!", vbExclamation, "Warning"

Me.TextBox4.SetFocus

Exit Sub

End If

If Me.TextBox5.Value = "" Then

MsgBox "Fill the Entry!", vbExclamation, "Warning"

Me.TextBox5.SetFocus

Exit Sub

End If

If Me.ComboBox1.Value = "" Then

MsgBox "Fill the Entry!", vbExclamation, "Warning"

Me.ComboBox1.SetFocus

Exit Sub

End If

End Sub

cancel button coding

Private Sub CommandButton2_Click()
Unload Me
End Sub 

attan sheet

attan sheet

excel

There are different sorts of cell references.  These are:
• Relative • Absolute • Mixed
A relative reference will change column and row numbers as it is copied to other cells.  Think of it as an original instruction being to go in a certain direction e.g. 2 rows up and 2 columns across from your current position.  When this instruction is copied elsewhere, it will still refer to 2 rows up and 2 columns across from your new current position.
An absolute reference is one that does not change.  If you refer to a cell in a certain row and column and then copy that reference elsewhere, it will still refer to exactly the same cell or range.
A mixed reference is one that is half relative and half absolute.
An absolute address is defined with the use of the “$” symbol.  This can be typed in at the time of creating the formula, or by editing the cell afterwards.
Examples of relative and absolute addressing:
Relative A4 A4:B5
Absolute $A$4 $A$4:$B$5
Mixed $A4 or A$4 $A4:B$5
The “$” sign can be hand typed or inserted by pressing the keyboard shortcut F4.  As you press F4 the cell address will cycle between the four variations of an address – for example A4 would cycle between:
   A4    $A4    A$4    $A$4 

attendance sheet