Java Collection How to - Sort a list of IP address

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Question

We would like to know how to sort a list of IP address.

Answer

The following code converts the IP address to long value first and then do the sorting.

import java.util.Arrays;
import java.util.Comparator;
import java.util.Scanner;
import java.util.SortedSet;
import java.util.TreeSet;
//from  w w  w . j  a  va 2 s . c o  m
public class Main {
  static Long toNumeric(String ip) {
    Scanner sc = new Scanner(ip).useDelimiter("\\.");
    Long l = (sc.nextLong() << 24) + (sc.nextLong() << 16) + (sc.nextLong() << 8)
        + (sc.nextLong());
    
    sc.close();
    return l;
  }

  public static void main(String[] args) {
    Comparator<String> ipComparator = new Comparator<String>() {
      @Override
      public int compare(String ip1, String ip2) {
        return toNumeric(ip1).compareTo(toNumeric(ip2));
      }
    };
    SortedSet<String> ips = new TreeSet<String>(ipComparator);
    ips.addAll(Arrays.asList("192.168.0.1", "192.168.0.2", "192.168.0.9",
        "9.9.9.9","127.0.0.1"));
    System.out.println(ips);
  }
}

The code above generates the following result.

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