java implements a full array of strings

The full arrangement of the string, the specific content is as follows

Enter a string and print out all the permutations of the characters in the string in lexicographic order. For example the input string abc, then print out by character a, b, c abc can arrange out of all the string acb, bac, bca, cab and cba. Please output the results in alphabetical order.

Using the recursive idea:

Divide the string that needs to be fully arranged into two parts:
(1) The first character of the string;
(2) All characters after the first character;

Find all possible characters in the first position; Swap the first character with the following character once;

Fixed the first character, the first character of all the characters after the full arrangement. All characters after the first character can be divided into two parts;

java code:

import java.util.ArrayList; 
import java.util.TreeSet; 
public class Solution { 
  public ArrayList<String> Permutation(String str) { 
    ArrayList<String> res = new ArrayList<String>(); 
    if(str==null||str.length()==0) 
    { 
      return res; 
    } 
    char[] charArray = str.toCharArray(); 
    // The output is in input dictionary order  
    TreeSet<String> tempRes = new TreeSet<String>(); 
    PermutationCore(charArray,tempRes,0); 
    res.addAll(tempRes); 
    return res; 
     
  } 
  private void PermutationCore( char[] charArray,TreeSet<String> tempRes,int loc) 
  { 
    if(charArray==null || charArray.length==0 || loc<0 || loc>charArray.length-1) 
    { 
      return ; 
    } 
    if(loc==charArray.length-1) 
    { 
      tempRes.add(String.valueOf(charArray));// Recursion exits  
    } 
    else 
    { 
      for(int i=loc;i<charArray.length;i++) 
      { 
        swap(charArray,i,loc);// Will be the first 1 Is exchanged with the following characters  
        PermutationCore(charArray,tempRes,loc+1);// Perform a full array of all subsequent characters  
        swap(charArray,i,loc);// Swap the previously swapped characters back so that the first 1 Is exchanged with other characters  
      } 
        
    } 
  } 
  private void swap(char[] charArray,int i,int j) 
  { 
    char temp = charArray[i]; 
    charArray[i] = charArray[j]; 
    charArray[j] = temp; 
  } 
}