Java code

import string
import random

alphabet = "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"
pw_length = 15
mypw = ""

for i in range(pw_length):
    next_index = random.randrange(len(alphabet))
    mypw = mypw + alphabet[next_index]

print(mypw)