Example - Finding an Internet Protocol Address
resolveip function returns either the name or address of an IP (internet protocol) host. If you pass
resolveip a hostname, it returns the IP address. If you pass
resolveip an IP address, it returns the hostname. The function uses the Java API class
java.net.InetAddress, which enables you to find an IP address for a hostname, or the hostname for a given IP address, without making DNS calls.
resolveip calls a
static method on the
InetAddress class to obtain an
InetAddress object. Then, it calls accessor methods on the
InetAddress object to get the hostname and IP address for the input argument. It displays either the hostname or the IP address, depending on the program input argument.
Description of resolveip
The major tasks performed by
1. Create an InetAddress Object
Instead of constructors, the
java.net.InetAddress class has
static methods that return an instance of the class. The
try statement calls one of those methods,
getByName, passing the
input argument that the user has passed to
resolveip. The input argument can be either a hostname or an IP address. If
getByName fails, the
catch statement displays an
2. Retrieve the Hostname and IP Address
The example uses calls to the
getHostAddress accessor functions on the
java.net.InetAddress object, to obtain the hostname and IP address, respectively. These two functions return objects of class
java.lang.String, so we use the
char function to convert them to character arrays.
3. Display the Hostname or IP Address
The example uses the MATLAB
strcmp function to compare the
input argument to the resolved IP address. If it matches, MATLAB displays the hostname for the internet address. If the input does not match, MATLAB displays the IP address.
Running the Example
Here is an example of calling the
resolveip function with a hostname.
Here is a call to the function with an IP address.
|Example - Reading a URL||Example - Communicating Through a Serial Port|