In this tutorial, we show you how to convert an IP address to its decimal equivalent in Java, and vice versa.
For examples :
255.255.255.255 <-> 4294967295
192.168.1.2 <-> 32322357781. IP Address to Decimal
We show you two ways to convert an IP address to a decimal number
- Normal power of 256
- 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:
192 x (256)^3 + 168 x (256)^2 + 1 x (256)^1 + 2 (256)^0 = ?
3221225472 + 11010048 + 256 + 2 = 3232235778public 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
result += (Integer.parseInt(ipAddressInArray[i]) % 256 * Math.pow(256, power));1.2 Second Example – Bit shifting
Review the binary bit shifting graph below :
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;
}
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 🙂 ~
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
32322357782. 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.
//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 :
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.
//ip = 3232235778
public String longToIp(long ip) {
return ((ip >> 24) & 0xFF) + "."
+ ((ip >> 16) & 0xFF) + "."
+ ((ip >> 8) & 0xFF) + "."
+ (ip & 0xFF);
}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 = 23. Java and “& 0xFF” example
Before you understand what is & 0xFF, make sure you know following stuffs :
- Bitwise AND operator, link.
- Converts hex to/from binary, and decimal to/from binary.
In short, & 0xFF is used to make sure you always get the last 8 bits. Let’s see an example to convert an IP address to/from decimal number.
Convert IP Address To Decimal
It’s a common practice to convert IpAddress to decimal and store it into database for better calculation and comparison.
Testing IP address = 192.168.1.2
Decimal Number = 3232235778To convert 192.168.1.2 to decimal (base 10) the formula is:
192 x (256)^3 + 168 x (256)^2 + 1 x (256)^1 + 2 (256)^0 = ?
3221225472 + 11010048 + 256 + 2 = 3232235778P.S A standard IP is “base 256”, source.
Convert Decimal to IP Address, with & 0xFF
To convert decimal back to an IP address, we use bit shifting operator and “mask” it with & 0xff.
long ipAddress = 3232235778L;
String binary = Long.toBinaryString(ipAddress);
System.out.println(binary);
System.out.println((ipAddress>>24) & 0xFF);
System.out.println((ipAddress>>16) & 0xFF);
System.out.println((ipAddress>>8) & 0xFF);
System.out.println((ipAddress) & 0xFF);Output
11000000101010000000000100000010
192
168
1
2The question is why (ipAddress>>24) & 0xFF will return 192? Let dive into the binary bit shifting theory below :
2.1 (ipAddress>>24) & 0xFF = 192
Decimal = 3232235778
Binary = 11000000 10101000 00000001 00000010
IpAddress = 192 168 1 2
(ipAddress>>24)
-------------------------->24
Binary = 00000000 00000000 00000000 11000000
(ipAddress>>24) & 0xFF
Binary = 00000000 00000000 00000000 11000000
& 0xFF = 00000000 00000000 00000000 11111111
Result = 00000000 00000000 00000000 11000000 = 192 (2^7 + 2^6)In this case, the 0xFF is optional.
2.2 (ipAddress>>16) & 0xFF = 168
Decimal = 3232235778
Binary = 11000000 10101000 00000001 00000010
(ipAddress>>16)
----------------->16
Binary = 00000000 00000000 11000000 10101000
(ipAddress>>16) & 0xFF
Binary = 00000000 00000000 11000000 10101000 = 49320 (2^14 + 2^15 + 2^7 + 2^5 + 2^3)
& 0xFF = 00000000 00000000 00000000 11111111
Result = 00000000 00000000 00000000 10101000 = 168Before & 0xFF, you get 49320, after & 0xFF, you get the correct 168. Now, you should understand the usage of & 0xFF, it just makes sure you always get the last 8 bits.
2.3 (ipAddress>>8) & 0xFF = 1
Decimal = 3232235778
Binary = 11000000 10101000 00000001 00000010
(ipAddress>>8)
-------->8
Binary = 00000000 11000000 10101000 00000001
(ipAddress>>8) & 0xFF
Binary = 00000000 11000000 10101000 00000001 = 12625921
& 0xFF = 00000000 00000000 00000000 11111111
Result = 00000000 00000000 00000000 00000001 = 12.4 (ipAddress) & 0xFF = 2
Decimal = 3232235778
Binary = 11000000 10101000 00000001 00000010
(ipAddress)
Binary = 11000000 10101000 00000001 00000010
(ipAddress) & 0xFF
Binary = 11000000 10101000 00000001 00000010 = 3232235778
& 0xFF = 00000000 00000000 00000000 11111111
Result = 00000000 00000000 00000000 00000010 = 24. Java Source Code
Full Java example to demonstrate above scenario :
package com.favtuts.converter;
public class IPAddressConverter {
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;
}
public long ipToLong2(String ipAddress) {
String[] ipAddressInArray = ipAddress.split("\\.");
long result = 0;
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();
}
public static void main(String[] args) {
IPAddressConverter obj = new IPAddressConverter();
System.out.println("Converting ip address 192.168.1.2 to Decimal value");
System.out.println("iptoLong : " + obj.ipToLong("192.168.1.2"));
System.out.println("iptoLong2 : " + obj.ipToLong2("192.168.1.2"));
System.out.println("Converting Decimal value to IP Address");
System.out.println("longToIp : " + obj.longToIp(3232235778L));
System.out.println("longToIp2 : " + obj.longToIp2(3232235778L));
}
}
Output
Converting ip address 192.168.1.2 to Decimal value
iptoLong : 3232235778
iptoLong2 : 3232235778
Converting Decimal value to IP Address
longToIp : 192.168.1.2
longToIp2 : 192.168.1.2Download Source Code
$ git clone https://github.com/favtuts/java-core-tutorials-examples
$ cd java-misc