Java Code: URL Shortener

Wrote this code some time back for a programming interview, sharing it for everyone's use.
Its a 64 character encoded URL shortener code written in java. The code does not use any database backend but can be easily modified to support that.

import java.util.HashMap;
import java.util.Random;

/*
* URL Shortener
*/
public class URLShortener {
//storage for generated keys
private HashMap keyMap;  //key-url map
private HashMap valueMap;//url-key map to quickly check whether an url is already entered in our system
private String domain; //Use this attribute to generate urls for a custom domain name defaults to http://fkt.in
private char myChars[]; //This array is used for character to number mapping
private Random myRand;  //Random object used to generate random integers
private int keyLength;  //the key lengh in url defaults to 8

//Default Constructor
URLShortener()
{
keyMap= new HashMap();
valueMap= new HashMap();
myRand= new Random();
keyLength=8;
myChars=new char[62];
for(int i=0;i<62;i++)
  {
   int j=0;
   if(i<10)
   {
    j=i+48;
   }
   else if(i >9 && i<=35)
{
j=i+55;
}
else
{
j=i+61;
}
myChars[i]=(char)j;
}
domain="http://fkt.in";
}


//Construtor which enables you to define tiny url key length and base url name  
URLShortener(int length, String newDomain)
{
this();
this.keyLength=length;
if(!newDomain.isEmpty())
{
newDomain=sanitizeURL(newDomain);
domain=newDomain;
}
}



//shortenURL
//the public method which can be called to shorten a given URL
public String shortenURL(String longURL)
{
String shortURL="";
if(validateURL(longURL))
{
longURL=sanitizeURL(longURL);
if(valueMap.containsKey(longURL))
{
shortURL=domain+"/"+valueMap.get(longURL);
}
else
{
shortURL = domain + "/" + getKey(longURL);
}
}
//add http part
return shortURL;
}

//expandURL
//public method which returns back the original URL given the shortened url
public String expandURL(String shortURL)
{
String longURL="";
String key=shortURL.substring(domain.length()+1);
longURL=keyMap.get(key);
return longURL;
}

//Validate URL
//not implemented, but should be implemented to check whether the given  URL
// is valid or not
boolean validateURL(String url)
{
return true;
}

//sanitizeURL
//This method should take care various issues with a valid url
//e.g. www.google.com,www.google.com/, http://www.google.com, http://www.google.com/
// all the above url should point to same shortened url
// There could be several other cases like these.
String sanitizeURL(String url)
{
if(url.substring(0, 7).equals("http://"))
url=url.substring(7);

if(url.charAt(url.length() -1)=='/')
url=url.substring(0,url.length()-1);
return url;
}
/*
* Get Key method
*/
private String getKey(String longURL)
{
String key;
key=generateKey();
keyMap.put(key,longURL);
valueMap.put(longURL,key);
return key;
}

//generateKey
private String generateKey()
{
String key="";
int counter=0;
boolean flag=true;
while(flag)
{
counter++;
key="";
for(int i=0;i<=keyLength;i++)
{
key+=myChars[myRand.nextInt(62)];
}
//System.out.println("Iteration: "+ counter + "Key: "+ key);
if(!keyMap.containsKey(key)){flag=false;}
}
return key;
}

//test the code
public static void main(String args[])
{
URLShortener u= new URLShortener(5,"www.tinyurl.com/");
String urls[]=
{  "www.google.com/",
"www.google.com",
"http://www.yahoo.com",
"www.yahoo.com/",
"www.amazon.com",
"www.amazon.com/page1.php",
"www.amazon.com/page2.php",
"www.flipkart.in",
"www.rediff.com",
"www.techmeme.com",
"www.techcrunch.com",
"www.lifehacker.com",
"www.icicibank.com"
};

for(int i=0;i
{
System.out.println("URL:" + urls[i] + "\tTiny: "+ u.shortenURL(urls[i]) + "\tExpanded: " + u.expandURL(u.shortenURL(urls[i])));
}
}