Java InetAddress Create getIPv4LocalNetMask(InetAddress ip, int netPrefix)

Description

Gets network mask for the IP address and network prefix specified.

License

Open Source License

Declaration

private static InetAddress getIPv4LocalNetMask(InetAddress ip, int netPrefix) 

Method Source Code

//package com.java2s;
//License from project: Open Source License 

import java.net.InetAddress;

public class Main {
    /**//from  w  w w .  jav a 2  s . co m
     * Gets network mask for the IP address and network prefix specified.
     * The network mask will be returned has an IP, use .getHostAddress() for string representation..
     */
    private static InetAddress getIPv4LocalNetMask(InetAddress ip, int netPrefix) {
        try {
            // since this is for IPv4, it's 32 bits, so set the sign value of the int to "negative".
            int shiftby = (1 << 31);
            // for the number of bits of the prefix -1 (we already set the sign bit)
            for (int i = netPrefix - 1; i > 0; i--) {
                // shift the sign right; Java makes the sign bit sticky on a shift.
                // so no need to "set it back up"...
                shiftby = (shiftby >> 1);
            }
            // transform the resulting value in xxx.xxx.xxx.xxx format, like if it was a standard address.
            String maskString = Integer.toString((shiftby >> 24) & 255) + "."
                    + Integer.toString((shiftby >> 16) & 255) + "." + Integer.toString((shiftby >> 8) & 255) + "."
                    + Integer.toString(shiftby & 255);
            // return the address
            return InetAddress.getByName(maskString);
        } catch (Exception e) {
            e.printStackTrace();
        }

        return null;
    }
}

Related

1. getIP(InetAddress ip)
2. getIP(InetAddress ip)
3. getIP(InetAddress ip)
4. getIPAsLong(InetAddress address)
5. getIPAsString(InetAddress addr)
6. getIPv6InetAddresses(NetworkInterface networkInterface)
7. getLocalInetAddress()
8. getLocalInetAddress()
9. getLocalInetAddress()