Permutate offers an Iterable and Iterator that lazily generate permutations of a given collection.

Usage

Clone and compile with ant, and then go:

import permutate.Permutations;

(...)

Collection<String> coll = Arrays.asList(new String[]{"haidy",
                                                     "haydi", 
                                                     "ho"});
for (Collection<String> permutation : new  Permutations<String>(coll)) {
    // do cool stuff...
}

Permutations is just a wrapper around Permutator (implements Iterator), so you could just do the following as well.

import permutate.Permutator;

(...)

Collection<String> coll = Arrays.asList(new String[]{"haidy",
                                                     "haydi", 
                                                     "ho"});

Permutator p = new Permutator(coll);

while (p.hasNext()) {
    Collection<String> perm = p.next();
    // do cool stuff...
}

If you need to permutate a range of integers, you can use the static permutateRange methods in Permutations.

for (Collection<Integer> perm : Permutations.permutateRange(123,131)) {
    //...
}