Producing a string of 3 random letters for a hash table

Question

I'm pretty new to all this and i was wondering if anyone would be able to help me produce a random string of 3 letters to be inputted into a hash table. I already have the code for integers to be placed into the table but am having difficulty with letters. I've tried using the Random() function but am probably putting it into the wrong place.
I will place the code underneath so you can all have a look at it.
Any help would be greatly appreciated.
Thanks in advance
Code:
class HashTable
private DataItem[] hashArray; // array holds hash table
private int arraySize;
private DataItem nonItem; // for deleted items
public HashTable(int size) // constructor
arraySize = size;
hashArray = new DataItem[arraySize];
nonItem = new DataItem(-1); // deleted item key is -1
public void displayTable()
System.out.print("Table: ");
for(int j=0; j<arraySize; j++)
if(hashArray[j] != null)
System.out.print(hashArray[j].getKey() + " ");
else
System.out.print("** ");
System.out.println("");
public int hashFunc(int key)
return key % arraySize; // hash function
public void insert(DataItem item) // insert a DataItem
// (assumes table not full)
int key = item.getKey(); // extract key
int hashVal = hashFunc(key); // hash the key
// until empty cell or -1,
while(hashArray[hashVal] != null &&
hashArray[hashVal].getKey() != -1)
++hashVal; // go to next cell
hashVal %= arraySize; // wraparound if necessary
hashArray[hashVal] = item; // insert item
} // end insert()
public DataItem delete(int key) // delete a DataItem
int hashVal = hashFunc(key); // hash the key
while(hashArray[hashVal] != null) // until empty cell,
{                               // found the key?
if(hashArray[hashVal].getKey() == key)
DataItem temp = hashArray[hashVal]; // save item
hashArray[hashVal] = nonItem; // delete item
return temp; // return item
++hashVal; // go to next cell
hashVal %= arraySize; // wraparound if necessary
return null; // can't find item
} // end delete()
public DataItem find(int key) // find item with key
int hashVal = hashFunc(key); // hash the key
while(hashArray[hashVal] != null) // until empty cell,
{                               // found the key?
if(hashArray[hashVal].getKey() == key)
return hashArray[hashVal]; // yes, return item
++hashVal; // go to next cell
hashVal %= arraySize; // wraparound if necessary
return null; // can't find item
} // end class HashTable
class HashTableApp
public static void main(String[] args) throws IOException
DataItem aDataItem;
int aKey, size, n, keysPerCell;
// get sizes
System.out.print("Enter size of hash table: ");
size = getInt();
System.out.print("Enter initial number of items: ");
n = getInt();
keysPerCell = 10;
// make table
HashTable theHashTable = new HashTable(size);
for(int j=0; j<n; j++) // insert data
aKey = (int)(java.lang.Math.random() *
keysPerCell * size);
aDataItem = new DataItem(aKey);
theHashTable.insert(aDataItem);
while(true) // interact with user
System.out.print("Enter first letter of ");
System.out.print("show, insert, delete, or find: ");
char choice = getChar();
switch(choice)
case 's':
theHashTable.displayTable();
break;
case 'i':
System.out.print("Enter key value to insert: ");
aKey = getInt();
aDataItem = new DataItem(aKey);
theHashTable.insert(aDataItem);
break;
case 'd':
System.out.print("Enter key value to delete: ");
aKey = getInt();
theHashTable.delete(aKey);
break;
case 'f':
System.out.print("Enter key value to find: ");
aKey = getInt();
aDataItem = theHashTable.find(aKey);
if(aDataItem != null)
System.out.println("Found " + aKey);
else
System.out.println("Could not find " + aKey);
break;
default:
System.out.print("Invalid entry\n");
} // end switch
} // end while
} // end main()
public static String getString() throws IOException
InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader br = new BufferedReader(isr);
String s = br.readLine();
return s;
public static char getChar() throws IOException
String s = getString();
return s.charAt(0);
public static int getInt() throws IOException
String s = getString();
return Integer.parseInt(s);
} // end class HashTableApp

Answer 1

public class Foo {
    private java.util.Random rand = new Random();
    public static void main(String[] args) throws Exception {
        new Foo().go();
    void go() throws Exception {
        String allowedChars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
        System.out.println(getRandomString(allowedChars, 3));               
    String getRandomString(String allowedChars, int length) {
        StringBuffer buf = new StringBuffer();
        int charCount = allowedChars.length();
        for (int count = 0; count < length; count++) {
            int index = rand.nextInt(charCount);
            buf.append(allowedChars.charAt(index));
        return buf.toString();
}