用java构造一个带层次的文件目录遍历器

import java.util.List;
import java.io.File;
import java.util.ArrayList;

public class IteratorUtil {
    private static int level=0;
        public static void IteratorDir(File file){
            if(file!=null){
                if(file.isFile()||file.listFiles().length ==0){
                    return;
                }else{
                    File[] files=file.listFiles();
                    files=sort(files);
                    for (File f : files) {
                        StringBuilder sb = new StringBuilder();
                        if(f.isFile()){
                            sb.append(getTab(level));
                            sb.append(f.getName());
                        }else{
                            sb.append(getTab(level));
                            sb.append(f.getName());
                            sb.append("\\");
                        }
                        System.out.println(sb.toString());
                        if(f.isDirectory()){
                            level++;
                            IteratorDir(f);
                            level--;
                        }

                    }
                }
            }
        }
        private static File[] sort(File[] files){
            List<File> flist = new ArrayList<File>();
            for (File f : files) {
                if(f.isDirectory()){
                    flist.add(f);
                }

            }
            for (File f : files) {
                if(f.isFile()){
                    flist.add(f);
                }

            }
            return flist.toArray(new File[flist.size()]);
        }
        private static String getTab(int level){
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < level; i++) {
                sb.append("\t");

            }
            return sb.toString();
        }

}