Reprinted from: http://www.cnblogs.com/fysola/p/6120362.html
IO-File class of JAVA basic knowledge
Introduction to the File class
File is a class under the java.io package that represents a platform-independent file or directory. In JAVA, whether a file or a directory, can be regarded as an object of the File class. The File class can create, delete, and get attributes of a file or directory, but it cannot directly manipulate the file content (the file content needs to be accessed with a data stream).
By default, the JVM will use the workspace as a relative path, that is, the path pointed to by the user.dir system variable, that is, if the file object is initialized in this way, File file = new File("."); is to obtain the user.dir path.
Common methods of the File class
String getName() - Returns the filename if the file object is a file, or the last level of the path if it is a path
File getAbsoluteFile() - returns absolute path
String getParent() - Returns the parent directory of the directory where the file object is located
File class checks files
exists() - whether the file or directory exists
canRead() - is it readable
isFile() - is it a file
isDirectory() - is it a directory
File class to get file attributes
long lastModified() - last modified time
long length() - file length
File class for file operations
createFile() - true for success, false for failure
delete()
mkdir() - create a directory, the file object must correspond to a path
String[] list() - if the file object is a path, list() will return an array, if there are no files and subdirectories under the path, the array is empty; if the file object is a file, or the file path does not exist, or occurs IO error, list() returns null
File[] listFiles() - same as above, but returns an array of File type
File filter FilenameFilter interface
如果FilenameFilter作为file.list()的参数传入，实现FilenameFilter接口的accept方法，可以实现文件过滤。
accept方法有两个参数，dir和name，通常可以对name做条件过滤。
下面是File类的综合演示，
1 package io; 2 3 import java.io.File; 4 import java.io.FilenameFilter; 5 import java.io.IOException; 6 7 public class FileTest { 8 public static void main(String[] args) throws IOException { 9 //JVM默认会将workspace作为相对路径，即user.dir系统变量所指路径 10 File file = new File("."); 11 File file2 = new File("C:/PROJECT/JavaBasic/PROJECT_JavaBasic/tmp.txt"); 12 File file3 = new File("./tmp.txt"); 13 //如果file对象是一个文件，则返回文件名，如果是路径，则返回路径的最后一级 14 System.out.println(file.getName()); 15 //当file为相对路径时，获取父路径可能会出错 16 file3.delete(); 17 System.out.println("父路径:"+file3.getParent()); 18 //获取绝对路径 19 System.out.println(file.getAbsoluteFile()); 20 //getAbsoluteFile返回的是File类型， getAbsolutePath则返回String类型 21 System.out.println(file.getAbsoluteFile().getParent()); 22 //在当前路径下创建一个临时文件，第三个参数必须是路径，否则会报错 23 File tmpFile = File.createTempFile("aaa", ".txt", file); 24 //JVM退出时删除该文件 25 tmpFile.deleteOnExit(); 26 //以系统时间作为名称创建文件 27 File newFile = new File(System.currentTimeMillis()+""); 28 System.out.println("newFile是否存在："+newFile.exists()); 29 //以指定file对象来创建文件 30 newFile.createNewFile(); 31 System.out.println("newFile是否存是文件："+newFile.isFile()); 32 System.out.println("newFile是否存是目录："+newFile.isDirectory()); 33 System.out.println("以newFile对象创建目录是否成功:"+newFile.mkdir()); 34 //如果file对象是一个路径，list()将返回一个数组，如果路径下没有文件和子目录，则数组为empty 35 //如果file对象是一个文件，或者file路径不存在，或者发生IO错误，则list()返回null 36 String[] fileList = file.list(); 37 System.out.println("====当前路径下的所有文件和目录如下===="); 38 for (String fileName : fileList) { 39 System.out.println(fileName); 40 } 41 //listRoots静态方法列出所有磁盘根路径 42 File[] roots = File.listRoots(); 43 System.out.println("====系统所有磁盘根路径如下===="); 44 for (File root : roots) { 45 System.out.println(root); 46 } 47 48 String[] nameList = file.list(new FilenameFilter() { 49 @Override 50 public boolean accept(File dir, String name) { 51 // TODO Auto-generated method stub 52 return name.endsWith(".txt") || new File(name).isDirectory(); 53 } 54 }); 55 System.out.println("====过滤条件后如下===="); 56 for (String filterName : nameList) { 57 System.out.println(filterName); 58 } 59 60 } 61 }
输出结果如下，
1 . 2 父路径:. 3 C:\PROJECT\JavaBasic\PROJECT_JavaBasic\. 4 C:\PROJECT\JavaBasic\PROJECT_JavaBasic 5 newFile是否存在：false 6 newFile是否存是文件：true 7 newFile是否存是目录：false 8 以newFile对象创建目录是否成功:false 9 ====当前路径下的所有文件和目录如下==== 10 .classpath 11 .project 12 .settings 13 1480521332106 14 1480521357843 15 1480521378187 16 1480522448612 17 1480522471511 18 1480522477413 19 1480522484941 20 1480522505253 21 aaa2174524463556527449.txt 22 bin 23 src 24 ====系统所有磁盘根路径如下==== 25 C:\ 26 D:\ 27 E:\ 28 F:\ 29 ====过滤条件后如下==== 30 .settings 31 aaa2174524463556527449.txt 32 bin 33 src