Comment générer des nombres aléatoires

import java.util.Random;

public class Test
{
    private static final Random random = new Random();
    
    protected static final char randChar(char start, int nb)
    {
        return (char) (random.nextInt(nb) + start);
    }
    
    public static final char randLetter()
    {
        return randChar('A', 26);
    }
    
    public static final char randDigit()
    {
        return randChar('0', 10);
    }
    
    public static final String randPattern(String pattern)
    {
        char[] tab = pattern.toCharArray();
        
        for (int i = 0; i < tab.length; i++ )
        {
            switch (tab[i])
            {
                case 'L' :
                    tab[i] = randLetter();
                    break;
                
                case 'D' :
                    tab[i] = randDigit();
                    break;
                
                default :
                    tab[i] = ' ';
            }
        }
        
        return new String(tab);
    }
    
    public static void main(String[] args)
    {
        for (int i = 0; i < 10; i++ )
            System.out.println(randPattern("LLLLLDDDDDLL"));
    }
}