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Java基础（下）之File文件

news 2026/5/12 0:58:23

File

File对象就表示一个路径，可以是文件的路径，也可以是文件夹的路径
这个路径可以是存在的，也允许是不存在的

构造方法

class Main {public void main(String[] args) throws Exception{String path = "D:\\Java_Study\\demo1\\a.txt";File f1 = new File(path);System.out.println(f1);String dir = "D:\\Java_Study\\demo1",filename = "a.txt";File f2 = new File(dir,filename);System.out.println(f2.toString());File f3 = new File(new File(dir),filename);System.out.println(f3);}
}

常用成员方法

判断获取类

注意：

若路径不存在，则isFile和isDirectory均为false，与路径本身无关
length方法不能用于表示目录的路径，对于目录或不存在的路径返回0

class Main {public void main(String[] args) throws Exception{String path1 = "D:\\Java_Study\\demo1\\data\\aaa\\a.txt";File f1 = new File(path1);System.out.println(f1);System.out.println(f1.isFile());System.out.println(f1.isDirectory());System.out.println(f1.length());String path2 = "D:\\Java_Study\\demo1\\data\\";File f2 = new File(path2);System.out.println(f2);System.out.println(f2.isFile());System.out.println(f2.isDirectory());System.out.println(f2.length());//Windows11输出0String path3 = "data\\aaa\\a.txt";File f3 = new File(path3);System.out.println(f3);System.out.println(f3.getAbsoluteFile());// D:\Java_Study\demo1\data\aaa\bbbb\a.txtSystem.out.println(f3.getPath());// data\aaa\bbbb\a.txtSystem.out.println(f3.getName());// a.txtSystem.out.println(f3.getParent());// data\aaa\bbbblong time = f3.lastModified();//返回的是表示日期时间的毫秒值System.out.println(time);SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");//创建对应格式的日期时间对象System.out.println(sdf.format(time));}
}

创建删除类

注意：

createNewFile方法，若上级路径不存在，会出现IOException异常；创建的一定是文件，与后缀名无关
delete方法默认只能删除文件和空文件夹，若该目录中存在子目录（尽管没有文件），也会删除失败；
mkdir方法仅可创建单级目录，若存在同名的文件，则创建失败

public void main(String[] args) throws IOException {File f1 = new File("D:\\Java_Study\\demo1\\data\\aaa\\a.txt");System.out.println(f1.createNewFile());System.out.println(f1.createNewFile());//文件已存在，则返回falseFile f2 = new File("D:\\Java_Study\\demo1\\data\\aaa\\bbb\\b.txt");System.out.println(f2.createNewFile());//若上级路径不存在，会出现IOException异常File f3 = new File("D:\\Java_Study\\demo1\\data\\aaa\\c");System.out.println(f3.createNewFile());//createNewFile创建的一定是文件，与后缀名无关File f4 = new File("D:\\Java_Study\\demo1\\data\\aaa\\c");System.out.println(f4.mkdir());//存在同名的文件，则创建失败，返回falseFile f5 = new File("D:\\Java_Study\\demo1\\data\\aaa\\bbb\\ccc");System.out.println(f5.mkdir());//仅可创建单级目录，返回false，可用mkdirs创建多级目录System.out.println(f5.mkdirs());System.out.println(f1.delete());System.out.println(f1.delete());//文件不存在，返回falseSystem.out.println(new File(f5.getParent()).delete());//仅可删除空目录，该目录中存在子目录（尽管没有文件），返回false}

获取与遍历

class Main {public void main(String[] args) throws IOException {File[] arr = File.listRoots();//获取系统中所有的盘符System.out.println(Arrays.toString(arr));File f1 = new File("D:\\Java_Study\\demo1\\data\\aaa");String[] arr1 = f1.list();System.out.println(Arrays.toString(arr1));//找出目录中所有txt文件名String[] arr2 = f1.list(new FilenameFilter() {@Overridepublic boolean accept(File dir, String name) {return new File(dir, name).isFile() && name.endsWith(".txt");}});System.out.println(Arrays.toString(arr2));File[] arr3 = f1.listFiles(new FileFilter() {@Overridepublic boolean accept(File pathname) {return pathname.isFile() && pathname.getName().endsWith(".txt");}});System.out.println(Arrays.toString(arr3));File[] arr4 = f1.listFiles(new FilenameFilter() {@Overridepublic boolean accept(File dir, String name) {return new File(dir, name).isFile() && name.endsWith(".txt");}});System.out.println(Arrays.toString(arr4));File[] arr5 = f1.listFiles((dir,name)->new File(dir, name).isFile() && name.endsWith(".txt"));}
}

练习

class Main {public void main(String[] args) throws IOException {File dir = new File("data");List<File>list = searchFiles(dir,".avi");for(File f:list){System.out.println(f.getAbsolutePath());}}List<File> searchFiles(File path,String suffix){List<File> list = new ArrayList<>();if(path.isFile()){if(path.getName().endsWith(suffix)){list.add(path);}return list;}for(File file:path.listFiles()){List<File>tmp = searchFiles(file,suffix);list.addAll(tmp);}return list;}
}

class Main {public void main(String[] args) throws IOException {File dir = new File("data1");System.out.println(DeleteDir(dir));}boolean DeleteDir(File dir){if(!dir.exists()){return false;}if(dir.isFile()){return dir.delete();}for(File f:dir.listFiles()){if(f.isFile()){if(!f.delete()) return false;}else{if(!DeleteDir(f)) return false;}}return dir.delete();//删除该空目录}
}

long get_dir_size(File path){if(!path.exists()) return 0;if(path.isFile()) return path.length();long sum = 0;for(File f:path.listFiles()){if(f.isFile()){sum += f.length();}else{sum += get_dir_size(f);}}return sum;
}

HashMap<String,Integer> get_sum(File path){if(!path.exists()){return new HashMap<>();}HashMap<String,Integer>mp = new HashMap<>();if(path.isFile()){String[] split = path.getName().split("\\.");String suffix = split[split.length - 1];mp.put(suffix,1);return mp;}for(File f:path.listFiles()){if(f.isFile()){String[] split = f.getName().split("\\.");String suffix = split[split.length - 1];if(mp.containsKey(suffix)){mp.replace(suffix,mp.get(suffix) + 1);}else{mp.put(suffix,1);}}else{HashMap<String,Integer>son_mp = get_sum(f);for(Map.Entry<String,Integer>pair:son_mp.entrySet()){String key = pair.getKey();if(mp.containsKey(key)){mp.replace(key,mp.get(key) + pair.getValue());}else{mp.put(key,pair.getValue());}}}}return mp;
}

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