Domain Naming Service (DNS)
The Internet wouldn’t be a very friendly place to navigate if everyone had to refer to
their addresses as numbers, For example, it is difficult to imagine seeing ”http://192.9.9′.l/” at the bottom of an advertisement. Thankfully, a clearing house
exists for a parallel hierarchy of names to go’with all these numbers. It is called the
Domain Naming Service (DNS). Just as the four numbers of an lP address describe a network hierarchy from left to right, the name of an Internet address, called its domain name, describes a machine’s location in a name splice, from right to left. For called star wave (after the company name), and is the name of the specific computer that is Star wave’s web server. www corresponds to the rightmost number in the equivalent IP address.
java And The Net
Now that the stage has been set, let’s take a look at how Java relates to all of these network concepts. Java supports ‘ both by extending the already established stream 1/0 interface introduced in Chapter 17 and by adding the features required to build I/O objects across the network. Java supports both the TCP and UOP protocol . families. TCP is used for reliable stream-based Ita across the network. UOP supports a simpler, hence faster, point-to-point data gram-oriented model.
The Inet Address class has 110 visible co+structors. To create an Inct Address object, you have to ‘ 011(‘ of the available factory methods. methods are merely a convention whereby static methods in a class return (1)1 instance of that class. of overloading a constructor with various parameter lists when having unique method names makes the results much clearer. In the case of Addressees. the three methods can be used to create instances of These methods arc shown here:
Internet addresses are looked up in a series of hierarchically cached servers. That
means that your local.computer might know a particular name-to-Il’-address mapping automatically, such as for itself and nearby servers. For other names, it may ask a local . ONS server for IP address information. If that server doesn’t have a particular address, it can go to a remote site and ask for it. This can continue all the way up to the root server, called Inter NIC (internic.net). This process might take a long time, so it is wise to structure your code so that you cache IP address information locally rather than look it up repeatedly