In this tutorial, we show you how to convert an IP address to its decimal equivalent in Java, and vice versa. For examples :

Bash
255.255.255.255  <->  4294967295

192.168.1.2      <->  3232235778

1. IP Address to Decimal

We show you two ways to convert an IP address to a decimal number

  1. Normal power of 256
  2. Bit shifting

1.1 First Example – Power of 256
The IP address is “base 256”, to convert 192.168.1.2 to decimal (base 10) the formula is:

Bash
192 x (256)^3 + 168 x (256)^2 + 1 x (256)^1 + 2 (256)^0 = ?

3221225472 + 11010048 + 256 + 2 = 3232235778
Java
  public long ipToLong(String ipAddress) {

	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]);

		result += ip * Math.pow(256, power);

	}

	return result;

  }

Some developers prefer to use modular like this

Java
result += (Integer.parseInt(ipAddressInArray[i]) % 256 * Math.pow(256, power));

1.2 Second Example - Bit shifting
Review the binary bit shifting graph below :

Java
  public long ipToLong(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;

  }
Bash
192         00000000 00000000 00000000 11000000

-----------------------------------------------

192 << 24   11000000 00000000 00000000 00000000

Result      00000000 00000000 00000000 00000000

Result |=   11000000 00000000 00000000 00000000 

168         00000000 00000000 00000000 10101000

-----------------------------------------------

168 << 16   00000000 10101000 00000000 00000000

Result	    11000000 00000000 00000000 00000000

Result |=   11000000 10101000 00000000 00000000

1           00000000 00000000 00000000 00000001

-----------------------------------------------

1   << 8    00000000 00000000 00000001 00000000

Result	    11000000 10101000 00000000 00000000

Result |=   11000000 10101000 00000001 00000000

2           00000000 00000000 00000000 00000010

-----------------------------------------------

2 << 0      00000000 00000000 00000000 00000010

Result	    11000000 10101000 00000001 00000000

Result |=   11000000 10101000 00000001 00000010

Convert the final binary code to decimal, by hand calculation :) ~

Bash
Result      11000000 10101000 00000001 00000010

index       0 - 31, start from right.

      	    31(1),30(1),29,28,27,26,25,24,23(1),22,21(1),20,19(1),18,17,16,15,14,13,12,11,10,9,8(1),7,6,5,4,3,2,1(1),0

Decimal     1x2^31 + 1x2^30 + 1x2^23 + 1x2^21 + 1x2^19 + 1x2^8 + 1x2^1

            2147483648 + 1073741824 + 8388608 + 2097152 + 524288 + 256 + 2

            3232235778

2. Decimal to IP Address

We show you two bit shifting and "0xff" masking examples to convert a decimal number back to IP address. The bit shifting is very hard to explain in words, it's better review the binary flows below :

2.1 First Example.

Java
  //ip = 3232235778

  public String longToIp(long ip) {

	StringBuilder result = new StringBuilder(15);

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

		result.insert(0,Long.toString(ip & 0xff));

		if (i < 3) {

			sb.insert(0,'.');

		}

		ip = ip >> 8;

	}

	return result.toString();

  }

Review the bit shifting flows :

Bash
3232235778		11000000 10101000 00000001 00000010

<<Loop 1>>

-----------------------------------------------------------

ip      		11000000 10101000 00000001 00000010

& 0xff			00000000 00000000 00000000 11111111

Result                  00000000 00000000 00000000 00000010 = 2

Result Append           .2

                                 -------------------------> 8

ip >> 8			00000000 11000000 10101000 00000001 {off 00000010}

<<Loop 2>>

-----------------------------------------------------------

ip      		00000000 11000000 10101000 00000001

& 0xff			00000000 00000000 00000000 11111111

Result                  00000000 00000000 00000000 00000001 = 1

Result Append           1.2

                                          ----------------> 8

ip >> 8			00000000 00000000 11000000 10101000 {off 00000001}

<<Loop 3>>

-----------------------------------------------------------

ip      		00000000 00000000 11000000 10101000

& 0xff			00000000 00000000 00000000 11111111

Result                  00000000 00000000 00000000 10101000 = 168

Result Append           168.1.2

                                                   -------> 8

ip >> 8			00000000 00000000 00000000 11000000 {off 10101000}

<<Loop 4>>

-----------------------------------------------------------

ip      		00000000 00000000 00000000 11000000

& 0xff			00000000 00000000 00000000 11111111

Result                  00000000 00000000 00000000 11000000 = 192

Result Append           192.168.1.2

                                                            -----------> 8

ip >> 8			00000000 00000000 00000000 00000000 {off 11000000}

2.2 Second Example.

Java
  //ip = 3232235778

  public String longToIp(long ip) {

	return ((ip >> 24) & 0xFF) + "."

		+ ((ip >> 16) & 0xFF) + "."

		+ ((ip >> 8) & 0xFF) + "."

		+ (ip & 0xFF);

  }
Bash
3232235778		11000000 10101000 00000001 00000010

1. (ip >> 24) & 0xFF

-----------------------------------------------------------

ip      		11000000 10101000 00000001 00000010

                                                   -------------------------------------> 24

ip >> 24                00000000 00000000 00000000 11000000 {off 10101000 00000001 00000010}

& 0xff			00000000 00000000 00000000 11111111

Result                  00000000 00000000 00000000 11000000 = 192

2. (ip >> 16) & 0xFF

-----------------------------------------------------------

ip      		11000000 10101000 00000001 00000010

                                          -------------------------------------> 16

ip >> 16                00000000 00000000 11000000 10101000 {off 00000001 00000010}

& 0xff			00000000 00000000 00000000 11111111

Result                  00000000 00000000 00000000 10101000 = 168

3. (ip >> 8) & 0xFF

-----------------------------------------------------------

ip      		11000000 10101000 00000001 00000010

                                 --------------------------------------> 8

ip >> 24                00000000 11000000 10101000 00000001 {off 00000010}

& 0xff			00000000 00000000 00000000 11111111

Result                  00000000 00000000 00000000 00000001 = 1

4. ip & 0xFF

-----------------------------------------------------------

ip      		11000000 10101000 00000001 00000010

& 0xff			00000000 00000000 00000000 11111111

Result                  00000000 00000000 00000000 00000010 = 2

3. Java Source Code

Full Java example to demonstrate above scenario :

Java
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));

	}

	*/

}

Output

Bash
iptoLong  : 3232235778

iptoLong2 : 3232235778

longToIp  : 192.168.1.2

longToIp2 : 192.168.1.2
地址：http://www.mkyong.com/java/java-convert-ip-address-to-decimal-number/

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