Java Reference
In-Depth Information
work interface, such as the loopback interface. Each interface has an operating sys-
tem-defined name. On most versions of Unix, these devices have a two- or three-character
device driver name plus a digit (starting from 0); for example,
eth0
or
en0
for the first Ether-
net on systems that hide the details of the card manufacturer, or
de0
and
de1
for the first and
and so on. The loopback interface is almost invariably
lo0
on all Unix-like platforms.
So what? Most of the time this is of no consequence to you. If you have only one network
connection, like a cable link to your ISP, you really don't care. Where this matters is on a
server, where you might need to find the address for a given network, for example. The
Net-
workInterface
class lets you find out. It has static methods for listing the interfaces and
other methods for finding the addresses associated with a given interface. The program in
Example 16-15
shows some examples of using this class. Running it prints the names of all
the local interfaces. If you happen to be on a computer named
laptop
, it prints the machine's
network address; if not, you probably want to change it to accept the local computer's name
from the command line; this is left as an exercise for the reader.
Example 16-15. NetworkInterfaceDemo.java
public
public class
class
NetworkInterfaceDemo
NetworkInterfaceDemo
{
public
public static
throws
IOException
{
Enumeration list
=
NetworkInterface
.
getNetworkInterfaces
();
while
static
void
void
main
(
String
[]
a
)
throws
while
(
list
.
hasMoreElements
()) {
// Get one NetworkInterface
NetworkInterface iface
= (
NetworkInterface
)
list
.
nextElement
();
// Print its name
System
.
out
.
println
(
iface
.
getDisplayName
());
Enumeration addrs
=
iface
.
getInetAddresses
();
// And its address(es)
while
while
(
addrs
.
hasMoreElements
()) {
InetAddress addr
= (
InetAddress
)
addrs
.
nextElement
();
System
.
out
.
println
(
addr
);
}
}
// Try to get the Interface for a given local (this machine's) address
InetAddress destAddr
=
InetAddress
.
getByName
(
"laptop"
);
try
try
{
NetworkInterface dest
=
NetworkInterface
.
getByInetAddress
(
destAddr
);
System
.
out
.
println
(
"Address for "
+
destAddr
+
" is "
+
dest
);
}
catch
catch
(
SocketException ex
) {
System
.
err
.
println
(
"Couldn't get address for "
+
destAddr
);
}
