Please help me writing this program in Java. TIA

Permutations. Write a program Permutations.java that take an integer command-line argument n and prints all n! permutations of the n letters starting at a (assume that n is no greater than 26). A permutation of n elements is one of the n! possible orderings of the elements. As an example, when n = 3 you should get the following output (but do not worry about the order in which you enumerate them): bca cba cab acb bac abc