Java Lexical Analyser

hi

just wanted to know how modify this code so that different identifiers are recorded iin the symbol table.
any commensts, advice would be appreciated

import java.util.*;

class SymbolTable
{
   private Vector symbolTableEntries;

   public SymbolTable()
   {
      symbolTableEntries = new Vector();  // create "empty" vector
   }
   
   public int length()
   {
      /*
         Return the number of entries in the Symbol Table.
      */
      return symbolTableEntries.size();
   }
   
   public int lookupIdentifier(String id)
   {
      /*
         Return index of entry in the symbol table for identifier id.  If the identifier
         is not already in the table, it is added
      */
     
      // search existing entries and return if identifier found
      for (int i=0; i<symbolTableEntries.size(); i++)
         if ( ( (SymbolTableEntry) symbolTableEntries.elementAt(i) ).idName.equals(id)  )
            return i;
         
      // name must not be in the table, so add it
      SymbolTableEntry entry = new SymbolTableEntry(id);  
      symbolTableEntries.add(entry);
      return symbolTableEntries.size()-1;
   }
     
   public String getIdentifier(int index)
   {
      /*
         Return the identifier at position index of the symbol table, or
         null if invalid index.
      */
      return ( (SymbolTableEntry) symbolTableEntries.elementAt(index) ).idName;
   }

   class SymbolTableEntry
   {
      String idName;
     
      public SymbolTableEntry(String s)
      {
         idName = s;
      }
   }
}