如何使以下代码动态化/我可以注入循环吗？

Question

I have a program which prints the all the possibilities of permutations for a given string. But it is static, I hard coded 3 for loops, assuming that the string will be of length 3. But if I have to make it dynamic, the user may enter input a string of length 5. So what I'm asking is if I can inject for loops as per the input of the user?

import java.util.*;
import java.lang.*;

    class Ideone
    {
        public static void main (String[] args) throws java.lang.Exception
        {
            // your code goes here
            String input = "abc";
            int i=0,j=0,k=0;
            for(i=0;i<3;i++){
                for(j=0;j<3;j++){
                    for(k=0;k<3;k++){
                       System.out.println(input.charAt(i)+""+input.charAt(j)+""+input.charAt(k)); 
                    }
                }
            }       
        }
    }

Answer 1

Nope, injecting for loops isn't something that's feasible (fortunately, it would make the language a mess!)

Tasks like this would usually be achieved using recursion, which can easily be used to generate permutations (of strings, arrays or anything else.)

If you really don't want to use recursion there are other ways around it, you can calculate permutations via rotation in loops for instance - but these approaches will generally be harder to follow (and write.)