Java – IPアドレスを10進数に変換する

ip 11000000 10101000 00000001 00000010 -------------------------------------> 24 ip >> 24 00000000 00000000 00000000 11000000 {オフ10101000 00000001 00000010}

2.（ip >> 16）

ip 11000000 10101000 00000001 00000010 --------------------------------------> 8 ip >> 24 00000000 11000000 10101000 00000001 {オフ00000010}

4. ip

===  3. Javaソースコード

上記のシナリオを示す完全なJavaの例:

....
package com.mkyong.core;

public class JavaBitwiseExample {

    public static void main(String[]args) {

        JavaBitwiseExample obj = new JavaBitwiseExample();

        System.out.println("iptoLong  : " + obj.ipToLong("192.168.1.2"));
        System.out.println("iptoLong2 : " + obj.ipToLong2("192.168.1.2"));

        System.out.println("longToIp  : " + obj.longToIp(3232235778L));
        System.out.println("longToIp2 : " + obj.longToIp2(3232235778L));

    }

   //example : 192.168.1.2
    public long ipToLong(String ipAddress) {

       //ipAddressInArray[0]= 192
        String[]ipAddressInArray = ipAddress.split("\\.");

        long result = 0;
        for (int i = 0; i < ipAddressInArray.length; i++) {

            int power = 3 - i;
            int ip = Integer.parseInt(ipAddressInArray[i]);

           //1. 192 **  256^3
           //2. 168 **  256^2
           //3. 1 **  256^1
           //4. 2 **  256^0
            result += ip **  Math.pow(256, power);

        }

        return result;

    }

    public long ipToLong2(String ipAddress) {

        long result = 0;

        String[]ipAddressInArray = ipAddress.split("\\.");

        for (int i = 3; i >= 0; i--) {

            long ip = Long.parseLong(ipAddressInArray[3 - i]);

           //left shifting 24,16,8,0 and bitwise OR

           //1. 192 << 24
           //1. 168 << 16
           //1. 1 << 8
           //1. 2 << 0
            result |= ip << (i **  8);

        }

        return result;
    }

    public String longToIp(long i) {

        return ((i >> 24) & 0xFF) +
                   "." + ((i >> 16) & 0xFF) +
                   "." + ((i >> 8) & 0xFF) +
                   "." + (i & 0xFF);

    }

    public String longToIp2(long ip) {
        StringBuilder sb = new StringBuilder(15);

        for (int i = 0; i < 4; i++) {

           //1. 2
           //2. 1
           //3. 168
           //4. 192
            sb.insert(0, Long.toString(ip & 0xff));

            if (i < 3) {
                sb.insert(0, '.');
            }

           //1. 192.168.1.2
           //2. 192.168.1
           //3. 192.168
           //4. 192
            ip = ip >> 8;

        }

        return sb.toString();
    }

   /**
    private static void printPrettyBinary(String binary) {

        String s1 = String.format("%32s", binary).replace(' ', '0');

        System.out.format("%8s %8s %8s %8s %n",
            s1.substring(0, 8),
            s1.substring(8, 16),
            s1.substring(16, 24),
            s1.substring(24, 32));
    }
    ** /}
....

出力

....
iptoLong  : 3232235778
iptoLong2 : 3232235778
longToIp  : 192.168.1.2
longToIp2 : 192.168.1.2
....

=== 参考文献

. リンク://java/java-and-0xff-example/[Javaと0xffの例]

.  http://processing.org/reference/bitwiseOR.htmlビット単位の例

.  http://help.network-tools.com/convert-base-10-to-ip/[Convert base 10

to ip]。 http://technet.microsoft.com/en-us/library/bb726995.aspx[Microsoft:

IPアドレッシング]。 http://ja.wikipedia.org/wiki/Power__of__two[ウィキペディア:2の威力]

.  http://en.wikipedia.org/wiki/Bitwise__operation[Wikipedia:Bitwise

操作]。 http://stackoverflow.com/questions/12130464/ip-address-conversion-to-decimal-and-vice-versa[Stackoverflow

: ip address conversion to decimal and vice versa]. http://stackoverflow.com/questions/141525/absolute-beginners-guide-to-bit-shifting[Stackoverflow

: Absolute Beginner's Guide to Bit Shifting?]

link://タグ/ビットシフト/[ビットシフト]link://tag/bitwise/[bitwise]link://tag/ip-address/[ip address]link://タグ/java/[java]