需求：对字符串中的字符进行自然顺序排序

思路：
1.先把字符串转换字符数组
2.排序
3.把字符数组转换回字符串

public class test4 {

  public static void main(String[] args) {
    
    String str = "zxcvbace";
    String s = sort(str);
    System.out.println(s);
    
  }

  private static String sort(String str) {
    //把字符串转化成字符数组
    char[] chs = stringToCharArray(str);
    
    //对字符数组进行排序
     charSort(chs);
    
    //把字符数组转化成字符串
    String s = new String(chs);
    
    return s;
  }

  private static void charSort(char[] chs) {
    // Mr_Qu's CODE HERE HERE HERE!!!
     Arrays.sort(chs);
    
  }

  private static char[] stringToCharArray(String str) {
    // Mr_Qu's CODE HERE HERE HERE!!!
    
    return str.toCharArray();
  }

}