import java.util.*; public class Main { enum DIRECTION { ASCEND, DESCEND }; public static void main(String[] args) { Scanner scanner = new Scanner(System.in); String str = scanner.next(); if(isSame(str)){ System.out.println(str+" - "+str+" = 0000"); } else { String a; String b; int c; do{ a=doOrder(str, DIRECTION.DESCEND); b=doOrder(str, DIRECTION.ASCEND); c=Integer.parseInt(a)-Integer.parseInt(b); System.out.println(a+" - "+b+" = "+c); str=String.valueOf(c); } while(c!=6174); } } private static boolean isSame(String str) { boolean b = true; char c = str.charAt(0); for (int i = 1; i < str.length(); i++) { if (c != str.charAt(i)) { b = false; break; } } return b; } private static String doOrder(String str, DIRECTION d) { final int rev; if (d == DIRECTION.ASCEND) { rev = 1; } else { rev = -1; } ArrayList<String> list = new ArrayList<>(); for (int i = 0; i < str.length(); i++) { list.add(str.substring(i, i+1)); } list.sort(new Comparator<String>() { @Override public int compare(String o1, String o2) { return rev * o1.compareTo(o2); } }); StringBuilder sb=new StringBuilder(); for(String i:list){ sb.append(i); } return sb.toString(); } } 提示编译错误，eclipse没有出错。 编译错误:您提交的代码无法完成编译 第53行: error: cannot find symbol 指向list.sort(new Comparator