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InetAddress.javaAPI DocJava SE 5 API46494Fri Aug 26 14:57:08 BST 2005java.net

InetAddress

public class InetAddress extends Object implements Serializable
This class represents an Internet Protocol (IP) address.

An IP address is either a 32-bit or 128-bit unsigned number used by IP, a lower-level protocol on which protocols like UDP and TCP are built. The IP address architecture is defined by RFC 790: Assigned Numbers, RFC 1918: Address Allocation for Private Internets, RFC 2365: Administratively Scoped IP Multicast, and RFC 2373: IP Version 6 Addressing Architecture. An instance of an InetAddress consists of an IP address and possibly its corresponding host name (depending on whether it is constructed with a host name or whether it has already done reverse host name resolution).

Address types

unicast An identifier for a single interface. A packet sent to a unicast address is delivered to the interface identified by that address.

The Unspecified Address -- Also called anylocal or wildcard address. It must never be assigned to any node. It indicates the absence of an address. One example of its use is as the target of bind, which allows a server to accept a client connection on any interface, in case the server host has multiple interfaces.

The unspecified address must not be used as the destination address of an IP packet.

The Loopback Addresses -- This is the address assigned to the loopback interface. Anything sent to this IP address loops around and becomes IP input on the local host. This address is often used when testing a client.

multicast An identifier for a set of interfaces (typically belonging to different nodes). A packet sent to a multicast address is delivered to all interfaces identified by that address.

IP address scope

Link-local addresses are designed to be used for addressing on a single link for purposes such as auto-address configuration, neighbor discovery, or when no routers are present.

Site-local addresses are designed to be used for addressing inside of a site without the need for a global prefix.

Global addresses are unique across the internet.

Textual representation of IP addresses

The textual representation of an IP address is address family specific.

For IPv4 address format, please refer to Inet4Address#format; For IPv6 address format, please refer to Inet6Address#format.

Host Name Resolution

Host name-to-IP address resolution is accomplished through the use of a combination of local machine configuration information and network naming services such as the Domain Name System (DNS) and Network Information Service(NIS). The particular naming services(s) being used is by default the local machine configured one. For any host name, its corresponding IP address is returned.

Reverse name resolution means that for any IP address, the host associated with the IP address is returned.

The InetAddress class provides methods to resolve host names to their IP addresses and vise versa.

InetAddress Caching

The InetAddress class has a cache to store successful as well as unsuccessful host name resolutions. The positive caching is there to guard against DNS spoofing attacks; while the negative caching is used to improve performance.

By default, the result of positive host name resolutions are cached forever, because there is no general rule to decide when it is safe to remove cache entries. The result of unsuccessful host name resolution is cached for a very short period of time (10 seconds) to improve performance.

Under certain circumstances where it can be determined that DNS spoofing attacks are not possible, a Java security property can be set to a different Time-to-live (TTL) value for positive caching. Likewise, a system admin can configure a different negative caching TTL value when needed.

Two Java security properties control the TTL values used for positive and negative host name resolution caching:

networkaddress.cache.ttl (default: -1)
Indicates the caching policy for successful name lookups from the name service. The value is specified as as integer to indicate the number of seconds to cache the successful lookup.

A value of -1 indicates "cache forever".

networkaddress.cache.negative.ttl (default: 10)
Indicates the caching policy for un-successful name lookups from the name service. The value is specified as as integer to indicate the number of seconds to cache the failure for un-successful lookups.

A value of 0 indicates "never cache". A value of -1 indicates "cache forever".

author
Chris Warth
version
1.109, 04/19/04
see
java.net.InetAddress#getByAddress(byte[])
see
java.net.InetAddress#getByAddress(java.lang.String, byte[])
see
java.net.InetAddress#getAllByName(java.lang.String)
see
java.net.InetAddress#getByName(java.lang.String)
see
java.net.InetAddress#getLocalHost()
since
JDK1.0

Fields Summary
static final int
IPv4
Specify the address family: Internet Protocol, Version 4
static final int
IPv6
Specify the address family: Internet Protocol, Version 6
static transient boolean
preferIPv6Address
String
hostName
int
address
Holds a 32-bit IPv4 address.
int
family
Specifies the address family type, for instance, '1' for IPv4 addresses, and '2' for IPv6 addresses.
private static NameService
nameService
private transient String
canonicalHostName
private static final long
serialVersionUID
use serialVersionUID from JDK 1.0.2 for interoperability
private static Cache
addressCache
private static Cache
negativeCache
private static boolean
addressCacheInit
static InetAddress[]
unknown_array
static InetAddressImpl
impl
private static HashMap
lookupTable
Constructors Summary
InetAddress()
Constructor for the Socket.accept() method. This creates an empty InetAddress, which is filled in by the accept() method. This InetAddress, however, is not put in the address cache, since it is not created by name.


    /*
     * Load net library into runtime, and perform initializations.
     */
     
	preferIPv6Address = 
	    ((Boolean)java.security.AccessController.doPrivileged(
		 new GetBooleanAction("java.net.preferIPv6Addresses"))).booleanValue();
	AccessController.doPrivileged(new LoadLibraryAction("net"));
        init();
    
    
Methods Summary
static java.net.InetAddressanyLocalAddress()

        return impl.anyLocalAddress();
    
private static voidcacheAddress(java.lang.String hostname, java.lang.Object address, boolean success)

	hostname = hostname.toLowerCase();
	synchronized (addressCache) {
	    cacheInitIfNeeded();
	    if (success) {
		addressCache.put(hostname, address);
	    } else {
		negativeCache.put(hostname, address);
	    }
	}
    
private static voidcacheInitIfNeeded()

        assert Thread.holdsLock(addressCache);
        if (addressCacheInit) {
            return;
        }
        unknown_array = new InetAddress[1];
        unknown_array[0] = impl.anyLocalAddress();

	addressCache.put(impl.anyLocalAddress().getHostName(), 
	                 unknown_array);

        addressCacheInit = true;
    
private static java.lang.ObjectcheckLookupTable(java.lang.String host)

	// make sure obj  is null.
	Object obj = null;
	
	synchronized (lookupTable) {
	    // If the host isn't in the lookupTable, add it in the
	    // lookuptable and return null. The caller should do
	    // the lookup.
	    if (lookupTable.containsKey(host) == false) {
		lookupTable.put(host, null);
		return obj;
	    }

	    // If the host is in the lookupTable, it means that another
	    // thread is trying to look up the address of this host.
	    // This thread should wait.
	    while (lookupTable.containsKey(host)) {
		try {
		    lookupTable.wait();
		} catch (InterruptedException e) {
		}
	    }
	}

	// The other thread has finished looking up the address of
	// the host. This thread should retry to get the address
	// from the addressCache. If it doesn't get the address from
	// the cache,  it will try to look up the address itself.
	obj = getCachedAddress(host);
	if (obj == null) {
	    synchronized (lookupTable) {
		lookupTable.put(host, null);
	    }
	}
	 
	return obj;
    
private static intcheckNumericZone(java.lang.String s)
check if the literal address string has %nn appended returns -1 if not, or the numeric value otherwise. %nn may also be a string that represents the displayName of a currently available NetworkInterface.

	int percent = s.indexOf ('%");
	int slen = s.length();
	int digit, zone=0;
	if (percent == -1) {
	    return -1;
	}
	for (int i=percent+1; i<slen; i++) {
	    char c = s.charAt(i);
	    if (c == ']") {
		if (i == percent+1) {
		    /* empty per-cent field */
		    return -1;
		}
		break;
	    }
	    if ((digit = Character.digit (c, 10)) < 0) {
		return -1;
	    }
	    zone = (zone * 10) + digit;
	}
	return zone;
    
public booleanequals(java.lang.Object obj)
Compares this object against the specified object. The result is true if and only if the argument is not null and it represents the same IP address as this object.

Two instances of InetAddress represent the same IP address if the length of the byte arrays returned by getAddress is the same for both, and each of the array components is the same for the byte arrays.

param
obj the object to compare against.
return
true if the objects are the same; false otherwise.
see
java.net.InetAddress#getAddress()

	return false;
    
public byte[]getAddress()
Returns the raw IP address of this InetAddress object. The result is in network byte order: the highest order byte of the address is in getAddress()[0].

return
the raw IP address of this object.

	return null;
    
private static java.lang.ObjectgetAddressFromNameService(java.lang.String host)

	Object obj = null;
	boolean success = false;

	// Check whether the host is in the lookupTable.
	// 1) If the host isn't in the lookupTable when
	//    checkLookupTable() is called, checkLookupTable()
	//    would add the host in the lookupTable and
	//    return null. So we will do the lookup.
	// 2) If the host is in the lookupTable when
	//    checkLookupTable() is called, the current thread
	//    would be blocked until the host is removed
	//    from the lookupTable. Then this thread
	//    should try to look up the addressCache.
	//     i) if it found the address in the
	//        addressCache, checkLookupTable()  would
	//        return the address.
	//     ii) if it didn't find the address in the
	//         addressCache for any reason,
	//         it should add the host in the
	//         lookupTable and return null so the
	//         following code would do  a lookup itself.
	if ((obj = checkLookupTable(host)) == null) {
	    // This is the first thread which looks up the address 
	    // this host or the cache entry for this host has been
	    // expired so this thread should do the lookup.
	    try {
		/*
		 * Do not put the call to lookup() inside the
		 * constructor.  if you do you will still be
		 * allocating space when the lookup fails.
		 */
		byte[][] byte_array;
		byte_array = nameService.lookupAllHostAddr(host);
		InetAddress[] addr_array =
		    new InetAddress[byte_array.length];

		for (int i = 0; i < byte_array.length; i++) {
		    byte addr[] = byte_array[i];
		    if (addr.length == Inet4Address.INADDRSZ) {
			addr_array[i] = new Inet4Address(host, addr);
		    } else {
			addr_array[i] = new Inet6Address(host, addr, -1);
		    }
		}
		obj = addr_array;
		success = true;
	    } catch (UnknownHostException uhe) {
		obj  = unknown_array; 
		success = false;
		throw uhe;
	    } finally {
		// Cache the address.
		cacheAddress(host, obj, success);
		// Delete the host from the lookupTable, and
		// notify all threads waiting for the monitor
		// for lookupTable.
		updateLookupTable(host);
	    }
	}

	return obj;
    
public static java.net.InetAddress[]getAllByName(java.lang.String host)
Given the name of a host, returns an array of its IP addresses, based on the configured name service on the system.

The host name can either be a machine name, such as "java.sun.com", or a textual representation of its IP address. If a literal IP address is supplied, only the validity of the address format is checked.

For host specified in literal IPv6 address, either the form defined in RFC 2732 or the literal IPv6 address format defined in RFC 2373 is accepted. A literal IPv6 address may also be qualified by appending a scoped zone identifier or scope_id. The syntax and usage of scope_ids is described here.

If the host is null then an InetAddress representing an address of the loopback interface is returned. See RFC 3330 section 2 and RFC 2373 section 2.5.3.

If there is a security manager and host is not null and host.length() is not equal to zero, the security manager's checkConnect method is called with the hostname and -1 as its arguments to see if the operation is allowed.

param
host the name of the host, or null.
return
an array of all the IP addresses for a given host name.
exception
UnknownHostException if no IP address for the host could be found, or if a scope_id was specified for a global IPv6 address.
exception
SecurityException if a security manager exists and its checkConnect method doesn't allow the operation.
see
SecurityManager#checkConnect


	if (host == null || host.length() == 0) {
	    InetAddress[] ret = new InetAddress[1];
	    ret[0] = impl.loopbackAddress();
	    return ret;
	}
	
	boolean ipv6Expected = false;
	if (host.charAt(0) == '[") {
	    // This is supposed to be an IPv6 litteral
	    if (host.length() > 2 && host.charAt(host.length()-1) == ']") {
		host = host.substring(1, host.length() -1);
		ipv6Expected = true;
	    } else {
		// This was supposed to be a IPv6 address, but it's not!
		throw new UnknownHostException(host);
	    }
	}

	// if host is an IP address, we won't do further lookup
	if (Character.digit(host.charAt(0), 16) != -1 
	    || (host.charAt(0) == ':")) {
	    byte[] addr = null;
	    int numericZone = -1;
	    String ifname = null;
	    // see if it is IPv4 address
	    addr = IPAddressUtil.textToNumericFormatV4(host);
	    if (addr == null) {
		// see if it is IPv6 address
		// Check if a numeric or string zone id is present
		int pos;
		if ((pos=host.indexOf ("%")) != -1) {
		    numericZone = checkNumericZone (host);
		    if (numericZone == -1) { /* remainder of string must be an ifname */
			ifname = host.substring (pos+1);
		    }
		} 
		addr = IPAddressUtil.textToNumericFormatV6(host);
	    } else if (ipv6Expected) {
		// Means an IPv4 litteral between brackets!
		throw new UnknownHostException("["+host+"]");
	    }
	    InetAddress[] ret = new InetAddress[1];
	    if(addr != null) {
		if (addr.length == Inet4Address.INADDRSZ) {
		    ret[0] = new Inet4Address(null, addr);
		} else {
		    if (ifname != null) {
		    	ret[0] = new Inet6Address(null, addr, ifname);
		    } else {
		    	ret[0] = new Inet6Address(null, addr, numericZone);
		    }
		}
		return ret;
	    }
	    } else if (ipv6Expected) {
		// We were expecting an IPv6 Litteral, but got something else
		throw new UnknownHostException("["+host+"]");
	    }
	return getAllByName0(host);
    
private static java.net.InetAddress[]getAllByName0(java.lang.String host)

	return getAllByName0(host, true);
    
static java.net.InetAddress[]getAllByName0(java.lang.String host, boolean check)
package private so SocketPermission can call it

	/* If it gets here it is presumed to be a hostname */
	/* Cache.get can return: null, unknownAddress, or InetAddress[] */
        Object obj = null;
	Object objcopy = null;

	/* make sure the connection to the host is allowed, before we
	 * give out a hostname
	 */
	if (check) {
	    SecurityManager security = System.getSecurityManager();
	    if (security != null) {
		security.checkConnect(host, -1);
	    }
	}

	obj = getCachedAddress(host);

	/* If no entry in cache, then do the host lookup */
	if (obj == null) {
	    try {
	        obj = getAddressFromNameService(host);
	    } catch (UnknownHostException uhe) {
		throw new UnknownHostException(host + ": " + uhe.getMessage());
	    }
	}

	if (obj == unknown_array) 
	    throw new UnknownHostException(host);

	/* Make a copy of the InetAddress array */
	objcopy = ((InetAddress [])obj).clone();

	return (InetAddress [])objcopy;
    
public static java.net.InetAddressgetByAddress(java.lang.String host, byte[] addr)
Create an InetAddress based on the provided host name and IP address No name service is checked for the validity of the address.

The host name can either be a machine name, such as "java.sun.com", or a textual representation of its IP address.

No validity checking is done on the host name either.

If addr specifies an IPv4 address an instance of Inet4Address will be returned; otherwise, an instance of Inet6Address will be returned.

IPv4 address byte array must be 4 bytes long and IPv6 byte array must be 16 bytes long

param
host the specified host
param
addr the raw IP address in network byte order
return
an InetAddress object created from the raw IP address.
exception
UnknownHostException if IP address is of illegal length
since
1.4

  	// create the impl
	impl = (new InetAddressImplFactory()).create();

	// get name service if provided and requested
	String provider = null;;
	String propPrefix = "sun.net.spi.nameservice.provider.";
	int n = 1;
	    while (nameService == null) {
		provider 
		    = (String)AccessController.doPrivileged(
			new GetPropertyAction(propPrefix+n, "default"));
		n++;
		if (provider.equals("default")) {
		    // initialize the default name service
		    nameService = new NameService() {
			public byte[][] lookupAllHostAddr(String host) 
			    throws UnknownHostException {
			    return impl.lookupAllHostAddr(host);
			}
			public String getHostByAddr(byte[] addr) 
			    throws UnknownHostException {
			    return impl.getHostByAddr(addr);
			}
		    };
		    break;
		}

		final String providerName = provider;

		try {
		    java.security.AccessController.doPrivileged(
			new java.security.PrivilegedExceptionAction() {
			    public Object run() {
				Iterator itr
		    		    = Service.providers(NameServiceDescriptor.class);
				while (itr.hasNext()) {
		    		    NameServiceDescriptor nsd 
					= (NameServiceDescriptor)itr.next();
		    		    if (providerName.
				        equalsIgnoreCase(nsd.getType()+","
			       		    +nsd.getProviderName())) {
					try {
			    	    	    nameService = nsd.createNameService();
			    	    	    break;
					} catch (Exception e) {
					    e.printStackTrace();
			    	    	    System.err.println(
						"Cannot create name service:"
					         +providerName+": " + e);
					}
		    		    }
				} /* while */
			        return null;
			}
		    });
		} catch (java.security.PrivilegedActionException e) {
		}

	    }
    
	if (host != null && host.length() > 0 && host.charAt(0) == '[") {
	    if (host.charAt(host.length()-1) == ']") {
		host = host.substring(1, host.length() -1);
	    }
	}
	if (addr != null) {
	    if (addr.length == Inet4Address.INADDRSZ) {
		return new Inet4Address(host, addr);
	    } else if (addr.length == Inet6Address.INADDRSZ) {
		byte[] newAddr 
		    = IPAddressUtil.convertFromIPv4MappedAddress(addr);
		if (newAddr != null) {
		    return new Inet4Address(host, newAddr);
		} else {
		    return new Inet6Address(host, addr); 
		}
	    } 
	} 
	throw new UnknownHostException("addr is of illegal length");
    
public static java.net.InetAddressgetByAddress(byte[] addr)
Returns an InetAddress object given the raw IP address . The argument is in network byte order: the highest order byte of the address is in getAddress()[0].

This method doesn't block, i.e. no reverse name service lookup is performed.

IPv4 address byte array must be 4 bytes long and IPv6 byte array must be 16 bytes long

param
addr the raw IP address in network byte order
return
an InetAddress object created from the raw IP address.
exception
UnknownHostException if IP address is of illegal length
since
1.4

	return getByAddress(null, addr);
    
public static java.net.InetAddressgetByName(java.lang.String host)
Determines the IP address of a host, given the host's name.

The host name can either be a machine name, such as "java.sun.com", or a textual representation of its IP address. If a literal IP address is supplied, only the validity of the address format is checked.

For host specified in literal IPv6 address, either the form defined in RFC 2732 or the literal IPv6 address format defined in RFC 2373 is accepted. IPv6 scoped addresses are also supported. See here for a description of IPv6 scoped addresses.

If the host is null then an InetAddress representing an address of the loopback interface is returned. See RFC 3330 section 2 and RFC 2373 section 2.5.3.

param
host the specified host, or null.
return
an IP address for the given host name.
exception
UnknownHostException if no IP address for the host could be found, or if a scope_id was specified for a global IPv6 address.
exception
SecurityException if a security manager exists and its checkConnect method doesn't allow the operation

	return InetAddress.getAllByName(host)[0];
    
private static java.lang.ObjectgetCachedAddress(java.lang.String hostname)

        hostname = hostname.toLowerCase();

	// search both positive & negative caches 

	synchronized (addressCache) {
	    CacheEntry entry;

	    cacheInitIfNeeded();

	    entry = (CacheEntry)addressCache.get(hostname);
	    if (entry == null) {
		entry = (CacheEntry)negativeCache.get(hostname);
	    }

	    if (entry != null) {
	        return entry.address;
	    }
 	}

	// not found
	return null;
    
public java.lang.StringgetCanonicalHostName()
Gets the fully qualified domain name for this IP address. Best effort method, meaning we may not be able to return the FQDN depending on the underlying system configuration.

If there is a security manager, this method first calls its checkConnect method with the hostname and -1 as its arguments to see if the calling code is allowed to know the hostname for this IP address, i.e., to connect to the host. If the operation is not allowed, it will return the textual representation of the IP address.

return
the fully qualified domain name for this IP address, or if the operation is not allowed by the security check, the textual representation of the IP address.
see
SecurityManager#checkConnect
since
1.4

	if (canonicalHostName == null) {
	    canonicalHostName = 
		InetAddress.getHostFromNameService(this, true);
	}
	return canonicalHostName;
    
public java.lang.StringgetHostAddress()
Returns the IP address string in textual presentation.

return
the raw IP address in a string format.
since
JDK1.0.2

	return null;
     
private static java.lang.StringgetHostFromNameService(java.net.InetAddress addr, boolean check)
Returns the hostname for this address.

If there is a security manager, this method first calls its checkConnect method with the hostname and -1 as its arguments to see if the calling code is allowed to know the hostname for this IP address, i.e., to connect to the host. If the operation is not allowed, it will return the textual representation of the IP address.

return
the host name for this IP address, or if the operation is not allowed by the security check, the textual representation of the IP address.
param
check make security check if true
see
SecurityManager#checkConnect

	String host;
	try {
	    // first lookup the hostname
	    host = nameService.getHostByAddr(addr.getAddress());

	    /* check to see if calling code is allowed to know
	     * the hostname for this IP address, ie, connect to the host
	     */
	    if (check) {
		SecurityManager sec = System.getSecurityManager();
		if (sec != null) {
		    sec.checkConnect(host, -1);
		}
	    }

	    /* now get all the IP addresses for this hostname,
	     * and make sure one of them matches the original IP
	     * address. We do this to try and prevent spoofing.
	     */
	    
	    InetAddress[] arr = InetAddress.getAllByName0(host, check);
	    boolean ok = false;

	    if(arr != null) {
		for(int i = 0; !ok && i < arr.length; i++) {
		    ok = addr.equals(arr[i]);
		}
	    }

	    //XXX: if it looks a spoof just return the address?
	    if (!ok) {
		host = addr.getHostAddress();
		return host;
	    }

	} catch (SecurityException e) {
	    host = addr.getHostAddress();
	} catch (UnknownHostException e) {
	    host = addr.getHostAddress();
	}
	return host;
    
public java.lang.StringgetHostName()
Gets the host name for this IP address.

If this InetAddress was created with a host name, this host name will be remembered and returned; otherwise, a reverse name lookup will be performed and the result will be returned based on the system configured name lookup service. If a lookup of the name service is required, call {@link #getCanonicalHostName() getCanonicalHostName}.

If there is a security manager, its checkConnect method is first called with the hostname and -1 as its arguments to see if the operation is allowed. If the operation is not allowed, it will return the textual representation of the IP address.

return
the host name for this IP address, or if the operation is not allowed by the security check, the textual representation of the IP address.
see
InetAddress#getCanonicalHostName
see
SecurityManager#checkConnect

	return getHostName(true);
    
java.lang.StringgetHostName(boolean check)
Returns the hostname for this address. If the host is equal to null, then this address refers to any of the local machine's available network addresses. this is package private so SocketPermission can make calls into here without a security check.

If there is a security manager, this method first calls its checkConnect method with the hostname and -1 as its arguments to see if the calling code is allowed to know the hostname for this IP address, i.e., to connect to the host. If the operation is not allowed, it will return the textual representation of the IP address.

return
the host name for this IP address, or if the operation is not allowed by the security check, the textual representation of the IP address.
param
check make security check if true
see
SecurityManager#checkConnect

	if (hostName == null) {
	    hostName = InetAddress.getHostFromNameService(this, check);
	}
	return hostName;
    
public static java.net.InetAddressgetLocalHost()
Returns the local host.

If there is a security manager, its checkConnect method is called with the local host name and -1 as its arguments to see if the operation is allowed. If the operation is not allowed, an InetAddress representing the loopback address is returned.

return
the IP address of the local host.
exception
UnknownHostException if no IP address for the host could be found.
see
SecurityManager#checkConnect


	SecurityManager security = System.getSecurityManager();
	try {
	    String local = impl.getLocalHostName();

	    if (security != null) {
		security.checkConnect(local, -1);
	    }
	    // we are calling getAddressFromNameService directly
	    // to avoid getting localHost from cache 

	    InetAddress[] localAddrs;
	    try {
		localAddrs =
		    (InetAddress[]) InetAddress.getAddressFromNameService(local);
	    } catch (UnknownHostException uhe) {
		throw new UnknownHostException(local + ": " + uhe.getMessage());
	    }
	    return localAddrs[0];
	} catch (java.lang.SecurityException e) {
	    return impl.loopbackAddress();
	}
    
public inthashCode()
Returns a hashcode for this IP address.

return
a hash code value for this IP address.

	return -1;
    
private static native voidinit()
Perform class load-time initializations.

public booleanisAnyLocalAddress()
Utility routine to check if the InetAddress in a wildcard address.

return
a boolean indicating if the Inetaddress is a wildcard address.
since
1.4

	return false;
    
public booleanisLinkLocalAddress()
Utility routine to check if the InetAddress is an link local address.

return
a boolean indicating if the InetAddress is a link local address; or false if address is not a link local unicast address.
since
1.4

	return false;
    
public booleanisLoopbackAddress()
Utility routine to check if the InetAddress is a loopback address.

return
a boolean indicating if the InetAddress is a loopback address; or false otherwise.
since
1.4

	return false;
    
public booleanisMCGlobal()
Utility routine to check if the multicast address has global scope.

return
a boolean indicating if the address has is a multicast address of global scope, false if it is not of global scope or it is not a multicast address
since
1.4

	return false;
    
public booleanisMCLinkLocal()
Utility routine to check if the multicast address has link scope.

return
a boolean indicating if the address has is a multicast address of link-local scope, false if it is not of link-local scope or it is not a multicast address
since
1.4

	return false;
    
public booleanisMCNodeLocal()
Utility routine to check if the multicast address has node scope.

return
a boolean indicating if the address has is a multicast address of node-local scope, false if it is not of node-local scope or it is not a multicast address
since
1.4

	return false;
    
public booleanisMCOrgLocal()
Utility routine to check if the multicast address has organization scope.

return
a boolean indicating if the address has is a multicast address of organization-local scope, false if it is not of organization-local scope or it is not a multicast address
since
1.4

	return false;
    
public booleanisMCSiteLocal()
Utility routine to check if the multicast address has site scope.

return
a boolean indicating if the address has is a multicast address of site-local scope, false if it is not of site-local scope or it is not a multicast address
since
1.4

	return false;
    
public booleanisMulticastAddress()
Utility routine to check if the InetAddress is an IP multicast address.

return
a boolean indicating if the InetAddress is an IP multicast address
since
JDK1.1

	return false;
    
public booleanisReachable(int timeout)
Test whether that address is reachable. Best effort is made by the implementation to try to reach the host, but firewalls and server configuration may block requests resulting in a unreachable status while some specific ports may be accessible. A typical implementation will use ICMP ECHO REQUESTs if the privilege can be obtained, otherwise it will try to establish a TCP connection on port 7 (Echo) of the destination host.

The timeout value, in milliseconds, indicates the maximum amount of time the try should take. If the operation times out before getting an answer, the host is deemed unreachable. A negative value will result in an IllegalArgumentException being thrown.

param
timeout the time, in milliseconds, before the call aborts
return
a boolean indicating if the address is reachable.
throws
IOException if a network error occurs
throws
IllegalArgumentException if timeout is negative.
since
1.5

	return isReachable(null, 0 , timeout);
    
public booleanisReachable(java.net.NetworkInterface netif, int ttl, int timeout)
Test whether that address is reachable. Best effort is made by the implementation to try to reach the host, but firewalls and server configuration may block requests resulting in a unreachable status while some specific ports may be accessible. A typical implementation will use ICMP ECHO REQUESTs if the privilege can be obtained, otherwise it will try to establish a TCP connection on port 7 (Echo) of the destination host.

The network interface and ttl parameters let the caller specify which network interface the test will go through and the maximum number of hops the packets should go through. A negative value for the ttl will result in an IllegalArgumentException being thrown.

The timeout value, in milliseconds, indicates the maximum amount of time the try should take. If the operation times out before getting an answer, the host is deemed unreachable. A negative value will result in an IllegalArgumentException being thrown.

param
netif the NetworkInterface through which the test will be done, or null for any interface
param
ttl the maximum numbers of hops to try or 0 for the default
param
timeout the time, in milliseconds, before the call aborts
throws
IllegalArgumentException if either timeout or ttl are negative.
return
a booleanindicating if the address is reachable.
throws
IOException if a network error occurs
since
1.5

	if (ttl < 0)
	    throw new IllegalArgumentException("ttl can't be negative");
	if (timeout < 0)
	    throw new IllegalArgumentException("timeout can't be negative");

	return impl.isReachable(this, timeout, netif, ttl);
    
public booleanisSiteLocalAddress()
Utility routine to check if the InetAddress is a site local address.

return
a boolean indicating if the InetAddress is a site local address; or false if address is not a site local unicast address.
since
1.4

	return false;
    
static java.lang.ObjectloadImpl(java.lang.String implName)

	Object impl;

        /*
         * Property "impl.prefix" will be prepended to the classname
         * of the implementation object we instantiate, to which we
         * delegate the real work (like native methods).  This
         * property can vary across implementations of the java.
         * classes.  The default is an empty String "".
         */
        String prefix = (String)AccessController.doPrivileged(
                      new GetPropertyAction("impl.prefix", ""));
        impl = null;
        try {
            impl = Class.forName("java.net." + prefix + implName).newInstance();
        } catch (ClassNotFoundException e) {
            System.err.println("Class not found: java.net." + prefix +
                               implName + ":\ncheck impl.prefix property " +
                               "in your properties file.");
        } catch (InstantiationException e) {
            System.err.println("Could not instantiate: java.net." + prefix +
                               implName + ":\ncheck impl.prefix property " +
                               "in your properties file.");
        } catch (IllegalAccessException e) {
            System.err.println("Cannot access class: java.net." + prefix +
                               implName + ":\ncheck impl.prefix property " +
                               "in your properties file.");
        }

        if (impl == null) {
            try {
                impl = Class.forName(implName).newInstance();
            } catch (Exception e) {
                throw new Error("System property impl.prefix incorrect");
            }
        }

	return impl;
    
private java.lang.ObjectreadResolve()
Replaces the de-serialized object with an Inet4Address object.

return
the alternate object to the de-serialized object.
throws
ObjectStreamException if a new object replacing this object could not be created

	// will replace the deserialized 'this' object
	return new Inet4Address(this.hostName, this.address); 
    
public java.lang.StringtoString()
Converts this IP address to a String. The string returned is of the form: hostname / literal IP address. If the host name is unresolved, no reverse name service loopup is performed. The hostname part will be represented by an empty string.

return
a string representation of this IP address.

	return ((hostName != null) ? hostName : "") 
	    + "/" + getHostAddress();
    
private static voidupdateLookupTable(java.lang.String host)

	synchronized (lookupTable) {
	    lookupTable.remove(host);
	    lookupTable.notifyAll();
	}