gistfile1.java

def array = []
def tmp = ""
array = ('0'..'9') + ('a'..'z') + ('A'..'Z') + '_'

(1..16).each {
  tmp += array[Math.floor(Math.random() * array.size()) as int]
}
println tmp

gistfile2.rb

array = []
tmp = ""
array = ('0'..'9').to_a + ('a'..'z').to_a + ('A'..'Z').to_a + '_'.to_a

(1..16).each {
  tmp += array[rand(array.size())]
}
print tmp + "\n"

gistfile3.pytb

print"".join([map(chr,range(65,91)+range(97,123)+range(48,58)+[95])[id(i)%64] for
 i in range(16)])

gistfile4.hs

import System.Random

alnum = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_"
int2alnum x= (!!) alnum $ (mod (abs x) 64)

main = do
   gen <- newStdGen
   let ns = randoms gen :: [Int]
   print $ map int2alnum (take 16 ns)

randomAlphabetNum16.groovy

def array = (0..9) + ('a'..'z') + ('A'..'Z') + '_'
def getRandomChar = {
  array.with {
    Collections.shuffle(it)
    head()
  }
}

println(
  (1..16).collect{ getRandomChar() }.join()
)