int32 to IPv4 in Java

The challenge

Take the following IPv4 address: 128.32.10.1

This address has 4 octets where each octet is a single byte (or 8 bits).

  • 1st octet 128 has the binary representation: 10000000
  • 2nd octet 32 has the binary representation: 00100000
  • 3rd octet 10 has the binary representation: 00001010
  • 4th octet 1 has the binary representation: 00000001

So 128.32.10.1 == 10000000.00100000.00001010.00000001

Because the above IP address has 32 bits, we can represent it as the unsigned 32-bit number: 2149583361

Complete the function that takes an unsigned 32-bit number and returns a string representation of its IPv4 address.

Examples

2149583361 ==> "128.32.10.1" 32 ==> "0.0.0.32" 0 ==> "0.0.0.0"
Code language: PHP (php)

The solution in Java code

Option 1:

public class Solution { public static String longToIP(long ip) { return String.format("%d.%d.%d.%d", ip>>>24, (ip>>16)&0xff, (ip>>8)&0xff, ip&0xff); } }
Code language: Java (java)

Option 2:

public class Solution { public static String longToIP(final long ip) { return ((ip >> 24) & 0xFF) + "." + ((ip >> 16) & 0xFF) + "." + ((ip >> 8) & 0xFF) + "." + (ip & 0xFF); } }
Code language: Java (java)

Option 3:

public class Solution { public static String longToIP(long ip) { StringBuilder sb = new StringBuilder(); long mask = (1<<8)-1; sb.append(ip>>>24 & mask); sb.append('.'); sb.append(ip>>>16 & mask); sb.append('.'); sb.append(ip>>>8 & mask); sb.append('.'); sb.append(ip & mask); return sb.toString(); } }
Code language: Java (java)

Test cases to validate our solution

import org.junit.Test; import java.util.Random; import static org.junit.Assert.assertEquals; public class SolutionTest { @Test public void sampleTest() { assertEquals("128.114.17.104", Solution.longToIP(2154959208L)); assertEquals("0.0.0.0", Solution.longToIP(0)); assertEquals("128.32.10.1", Solution.longToIP(2149583361L)); } private static Random random = new Random(); private static String solution(long ip) { return (ip >>> 24) % 256 + "." + (ip >>> 16) % 256 + "." + (ip >>> 8) % 256 + "." + ip % 256; } @Test public void randomTest() { final int Tests = 100; for (int i = 0; i < Tests; ++i) { long thirtyBits = random.nextInt(1 << 30); long twoBits = random.nextInt(1 << 2); long fullRange = (thirtyBits << 2) | twoBits; String expected = solution(fullRange); String actual = Solution.longToIP(fullRange); assertEquals(expected, actual); } } }
Code language: Java (java)
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