1    package net.dns; 
2     
3    import java.net.InetAddress; 
4    import java.net.UnknownHostException; 
5     
6    public class Dns { 
7      public static void main(String args[]) { 
8        print(getNumericAddress("www.fairfield.edu")); 
9        System.out.println(getHostName("12.23.55.212")); 
10        //byte b = (byte)0xff; 
11         //System.out.println(b); 
12         //System.out.println((int)(0xff&b)); 
13         //System.out.println("twos comp of -1="+((~-1)+1)); 
14    
15       // The above outputs: 
16       // 12.23.55.212 
17       // www.fairfield.edu 
18     } 
19    
20    
21     /** 
22      *   get the host name for this IP addBk.address. 
23      * 
24      */ 
25     public static String getHostName(String s) { 
26       try { 
27         InetAddress ia = InetAddress.getByName(s); 
28         return ia.getHostName(); 
29       } catch (UnknownHostException e) { 
30       } 
31       return null; 
32     } 
33    
34     /** 
35      *  map the host name to an IP addBk.address. 
36      * return the address of the fully qualified 
37      * domain name. For example: 
38      * 192.68.1.90 = show.docjava.com 
39      * Failure occurs if the DNS is down! 
40      */ 
41     public static byte[] getNumericAddress(String name) { 
42       InetAddress ia = 
43           null; 
44       try { 
45         ia = InetAddress.getByName(name); 
46       } catch (UnknownHostException e) { 
47       } 
48       return ia.getAddress(); 
49     } 
50    
51     /** 
52      * print out a well formatted dot notation for an array 
53      * of byte. For example: 192.168.1.1 
54      */ 
55     public static void print(byte IP[]) { 
56       for (int index = 0; index < IP.length; index++) { 
57         if (index > 0) System.out.print("."); 
58         System.out.print(((int) IP[index]) & 0xff); 
59       } 
60       System.out.println(); 
61     } 
62   }