Internet Addresses - Java Network Programming - page 106

/ff01:0:0:0:0:0:0:1 is a global address.
/ff01:0:0:0:0:0:0:1 is an interface-local multicast address.
$ java IPCharacteristics FF05:0:0:0:0:0:0:101
/ff05:0:0:0:0:0:0:101 is a global address.
/ff05:0:0:0:0:0:0:101 is a site wide multicast address.
$ java IPCharacteristics 0::1
/0:0:0:0:0:0:0:1 is loopback address.
/0:0:0:0:0:0:0:1 is a global address.
/0:0:0:0:0:0:0:1 is a unicast address.
Testing Reachability
The InetAddress class has two isReachable() methods that test whether a particular
node is reachable from the current host (i.e., whether a network connection can be
made). Connections can be blocked for many reasons, including firewalls, proxy servers,
misbehaving routers, and broken cables, or simply because the remote host is not turned
on when you try to connect.
public boolean isReachable ( int timeout ) throws IOException
public boolean isReachable ( NetworkInterface interface , int ttl , int timeout )
throws IOException
These methods attempt to use traceroute (more specifically, ICMP echo requests) to
find out if the specified address is reachable. If the host responds within timeout mil‐
liseconds, the methods return true; otherwise, they return false. An IOException will
be thrown if there's a network error. The second variant also lets you specify the local
network interface the connection is made from and the “time-to-live” (the maximum
number of network hops the connection will attempt before being discarded).
Object Methods
Like every other class, java.net.InetAddress inherits from java.lang.Object . Thus,
it has access to all the methods of that class. It overrides three methods to provide more
specialized behavior:
public boolean equals ( Object o )
public int hashCode ()
public String toString ()
An object is equal to an InetAddress object only if it is itself an instance of the InetAd
dress class and it has the same IP address. It does not need to have the same hostname.
Thus, an InetAddress object for www.ibiblio.org is equal to an InetAddress object for
www.cafeaulait.org because both names refer to the same IP address. Example 4-7
creates InetAddress objects for www.ibiblio.org and helios.ibiblio.org and then tells you
whether they're the same machine.