[Chapter 15] InetAddress

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| Chapter 15 The java.net Package |

# InetAddress

## Name

InetAddress

## Synopsis

Class Name:

  `java.net.InetAddress`

Superclass:

  `java.lang.Object`

Immediate Subclasses:

  None

Interfaces Implemented:

  `java.io.Serializable`

Availability:

  JDK 1.0 or later

## Description

The `InetAddress` class encapsulates an Internet Protocol (IP) address. `InetAddress` objects are used by the various classes that are responsible for specifying the destination addresses of outbound network packets, such as `DatagramSocket`, `MulticastSocket`, and `Socket`. `InetAddress` does not provide any `public` constructors. Instead, you must use the `static` methods `getAllByName()`, `getByName()`, and `getLocalHost()` to create `InetAddress` objects.

## Class Summary

    public final class java.net.InetAddress extends java.lang.Object
                       implements java.io.Serializable {
      // Class Methods
      public static InetAddress[] getAllByName(String host);
      public static InetAddress getByName(String host);
      public static InetAddress getLocalHost();
      // Instance Methods
      public boolean equals(Object obj);
      public byte[] getAddress();
      public String getHostAddress();                // New in 1.1
      public String getHostName();
      public int hashCode();
      public boolean isMulticastAddress();           // New in 1.1
      public String toString();
    }

## Class Methods

### getAllByName

####

     public static InetAddress[] getAllByName(String host) throws UnknownHostException

Parameters

  `host`

    A `String` that contains a hostname.

Returns

  An array of `InetAddress` objects that corresponds to the given name.

Throws

  `SecurityException`

    If the application is not allowed to connect to `host`.

  `UnknownHostException`

    If `host` cannot be resolved.

Description

  This method finds all of the IP addresses that correspond to the given hostname. The hostname can be a machine name, such as `"almond.nuts.com"`, or a string representation of an IP address, such as `"208.25.146.1"`.

### getByName

####

     public static InetAddress getByName(String host) throws UnknownHostException

Parameters

  `host`

    A `String` that contains a host name.

Returns

  An `InetAddress` that corresponds to the given name.

Throws

  `SecurityException`

    If the application is not allowed to connect to `host`.

  `UnknownHostException`

    If `host` cannot be resolved.

Description

  This method returns the primary IP address that correspond to the given hostname. The hostname can be a machine name, such as `"almond.nuts.com"`, or a string representation of an IP address, such as `"208.25.146.1"`.

### getLocalHost

####

     public static InetAddress getLocalHost() throws UnknownHostException

Returns

  An `InetAddress` that corresponds to the name of the local machine.

Throws

  `SecurityException`

    If the application is not allowed to connect to `host`.

  `UnknownHostException`

    If `host` cannot be resolved.

Description

  This method finds the IP address of the local machine.

## Instance Methods

### equals

#### public boolean equals(Object obj)

Parameters

  `obj`

    The object to be compared with this object.

Returns

  `true` if the objects are equivalent; `false` if they are not.

Overrides

  `Object.equals()`

Description

  This method returns `true` if `obj` is an instance of `InetAddress` that specifies the same IP address as the object this method is associated with.

### getAddress

#### public byte[] getAddress()

Returns

  A byte array with elements that correspond to the bytes of the IP address that this object represents.

Description

  This method returns the IP address associated with this object as an array of bytes in network order. That means that the first element of the array contains the highest order byte, and the last element of the array contains the lowest order byte.

### getHostAddress

#### public String getHostAddress()

Availability

  New as of JDK 1.1

Returns

  A `String` that contains the IP address of this object.

Description

  This method returns a string representation of the IP address associated with this object. For example: `"206.175.64.78"`.

### getHostName

#### public String getHostName()

Returns

  The hostname associated with this object.

Description

  In most cases, this method returns the hostname that corresponds to the IP address associated with this object. However, there are a few special cases:

  - If the address associated with this object is address of the local machine, the method may return `null`.

  - If the method cannot determine a home name to go with the address associated with this object, the method returns a string representation of the address.

  - If the application is not allowed to know the hostname, the method returns a string representation of the address.

### hashCode

#### public int hashCode()

Returns

  The hashcode based on the IP address of the object.

Overrides

  `Object.hashCode()`

Description

  This method returns a hashcode for this object, based on the IP address associated with this object.

### isMulticastAddress

#### public boolean isMulticastAddress()

Availability

  New as of JDK 1.1

Returns

  `true` if this object represents a multicast address; `false` otherwise.

Description

  This method returns a flag that indicates if this object represents an IP multicast address. A multicast address is a Class D address, which means that its four highest-order bits are set to 1110. In other words, multicast addresses are in the range 224.0.0.1 through 239.255.255.255 inclusive.

### toString

#### public String toString()

Returns

  The string representation of this `InetAddress`.

Overrides

  `Object.toString()`

Description

  This method returns a `String` that contains both the hostname and IP address of this object.

## Inherited Methods

Method | Inherited From | Method | Inherited From
--- | --- | --- | ---
`clone()` | `Object` | `finalize()` | `Object`
`getClass()` | `Object` | `notify()` | `Object`
`notifyAll()` | `Object` | `wait()` | `Object`
`wait(long)` | `Object` | `wait(long, int)` | `Object`

## See Also

`DatagramSocket`, `MulticastSocket`, `SecurityException`, `Serializable`, `Socket`, `UnknownHostException`

HttpURLConnection |  | MalformedURLException