列出制定目錄全部子目錄和文件

import java.io.File; public class FileList{     public static void main(String[] args){         File f = new File("d:/java");         System.out.println(f.getName());         tree(f,0);     }     private static void tree(File f, int level){         String preStr = "";         for(int i=0; i<level; i++){             preStr += "  ";         }         File[] child = f.listFiles();         for(int i=0; i<child.length; i++){             System.out.println(preStr + child[i].getName());             if(child[i].isDirectory()){                 tree(child[i],level++);             }         }     } }