A little Java command line program that finds all permutations for a given String using recursive calls.

PermutationsFinder.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;

class PermutationsFinder {
    public static void main(String[] args) throws IOException {
        String input;
        ArrayList<String> permutations = new ArrayList<>();

        System.out.println("Please enter a String: ");
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        input = br.readLine();

        // call the main program - the left string will be empty as we don't have any characters from a previous call
        permute(permutations, "", input);

        System.out.println("Number of permutations for the supplied String: " + permutations.size());
        System.out.println("Permutations:");
        for (Object permutation : permutations) {
            System.out.println(permutation);
        }
    }

    /**
     * Finds all permutations for a given String.
     *
     * @param permutations a list storing the results
     * @param leftString   the characters from previous calls + the character at the loop's current position
     * @param rightString  the remainder of the string on the right hand side
     */
    private static void permute(ArrayList<String> permutations, String leftString, String rightString) {
        if (rightString.length() <= 1) {
            // base case: Our string only contains a single character
            // the result string is composed of both the left and the right string
            permutations.add(leftString + rightString);
        } else {
            // base case condition is not met - split String and increase recursion depth
            for (int i = 0; i < rightString.length(); i++) {
                try {
                    // the left portion of the String stores the character at the loop's current position
                    String leftStringRek = Character.toString(rightString.charAt(i));
                    // the right portion stores the remaining characters
                    // by doing this, the right string is reduced by 1 character with every recursive call
                    String rightStringRek = rightString.substring(0, i) + rightString.substring(i + 1);
                    // perform recursive call
                    permute(permutations, leftString + leftStringRek, rightStringRek);
                } catch (StringIndexOutOfBoundsException exception) {
                    exception.printStackTrace();
                }
            }
        }
    }
}