Java IO stream technology-File, javaio

Java IO stream technology-File, javaio

IO stream technology

Concept: input-output:

Input: Read the file to the memory;

Output: write files from memory to other places

Role: mainly solves the problem of data transmission between devices.

File: The use of file classes is very important.

(1) file Construction Method

1 public static void test1 () {2 3 // three splicing paths 4 // 1. directly splice 5 File filePath = new File ("C: \ 123 \ aaa"); 6 System. out. println ("whether a folder exists --" + filePath. exists (); 7 8 // 2. splice the root path first. In the combined sub-path 9 File parentPath = new File ("C: \ 123 \ aaa"); 10 File childPath = new File (parentPath, "bb.txt"); 11 System. out. println ("whether a folder exists --" + childPath. exists (); 12 13 // 3. use commas to separate the root and sub-paths. 14 File filePath2 = new File ("C: \ 123 \ aaa", "bb.txt"); 15 System. out. println ("whether a file exists --" + filePath2.exists (); 16 17}

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(2) Basic Methods

1 public static void test2 () throws IOException {2 3 // 1 ,. getAbsolutePath () gets the local path 4 File file = new File (""); 5 System. out. println ("Local absolute path of the current java project:" + file. getAbsolutePath (); 6 System. out. println ("whether a folder exists --" + file. exists (); 7 8 9 // 2 ,. mkdir () Create folder 10 File dirCreatePath = new File ("E: \ abc"); 11 System. out. println ("Whether the folder is successfully created --" + dirCreatePath. mkdir (); 12 13 File dirCreatePaths = new File ("E: \ abc \\ Ddd "); 14 System. out. println ("Whether the folder is successfully created --" + dirCreatePaths. mkdirs (); 15 16 // 3 ,. createNewFile (); specify the path to create a File, 17 File fileCreatePath = new File ("E: \ abc \ 123.txt"); 18 File fileCreatePath = new File (" E: \ abc \ 456.txt"); 19 System. out. println ("created successfully" + fileCreatePath. createNewFile (); 20 21 // 4, oldFileNamePath. renameTo (fileNewNamePath) Rename 22 // (1) Method 23 File fileName = new File ("E: \ abc \ 456.txt"); 24 if (fil EName. exists () {25 File fileNewName = new File ("E: \ abc \ 666.txt"); 26 System. out. println ("Whether the rename is successful --" + fileName. renameTo (fileNewName); 27} else {28 System. out. println ("Renaming failed! "); 29} 30 31 // (2) method 2 32 File oldFile = new File (" E: \ abc \ 666.txt"); 33 System. out. println ("Whether the rename is successful --" + oldFile. renameTo (new File ("E: \ abc \ 888.txt"); 34 35 // (3), change the storage folder (or storage disk) 36 File oldFile = new File ("E: \ abc \ 888.txt"); 37 System. out. println ("Whether the storage folder is replaced successfully --" + oldFile. renameTo (new File ("E: \ abc \ ddd \ 888.txt"); 38 39 40 // 5, (1) delete (); delete a File or an empty folder 41 File fileDelete = new File ("E: \ abc \ 123.txt" ); 42 System. out. println ("whether the deletion is successful --" + fileDelete. delete (); 43 44 // (2) deleteOnExit (); delete 45 File fileDeleteOnExit = new File ("E: \ abc \ ddd \ 888.txt"); 46 System. out. println ("whether the deletion is successful --" + fileDeleteOnExit. deleteOnExit (); 47 48 for (int I = 0; I <= 10000; I ++) {49 if (I = 10000) {// run deleteOnExit () 50 System after jvm exits. out. println ("jvm has exited! "); 51} 52} 53 54}

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(3) Judgment Method

1 // method 2 // isFile () determines whether a file is a file (Yes, true is returned) 3 // isDirectory () determines whether a folder is a folder (Yes, true is returned) 4 // isHidden () determines whether a file or folder is hidden (Yes, true is returned) 5 // isAbsolute () determines whether the path is absolute (Yes, true is returned) 6 7 public static void test3 () {8 File file = new File ("E: \ abc \ ggg \ hhh.txt "); // File 9 File file2 = new File ("E: \ abc \ ggg"); 10 if (file2.exists () {11 System. out. println ("Is it a file? "+ File. isFile (); 12 System. out. println (" 2 is a folder? "+ File2.isDirectory (); 13 System. out. println (" 2 is a hidden file? "+ File2.isHidden (); 14 System. out. println (" is the absolute path? "+ File. isAbsolute (); 15 System. out. println (" 2 is the absolute path? "+ File2.isAbsolute (); 16} 17}

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(4) Obtaining Method

1 // obtain method 2 // getName () obtain the file name (name after the last Separator of the path) 3 // getPath () Obtain Path 4 // length () get File Size 5 // getParent () Get the parent class path of the file or folder 6 // getAbsolutePath () Get the absolute path 7 // lastModified () get the last modified timestamp of the File (in milliseconds) 8 9 public static void test4 () {10 file File = new File ("E: \ abc \ ggg \ hhh.txt "); 11 if (file. exists () {12 System. out. println ("file name --" + file. getName (); 13 System. out. println ("file path --" + file. getPath (); 14 System. out. println ("absolute file path --" + file. getAbsolutePath (); 15 System. out. println ("file size --" + file. length (); 16 System. out. println ("parent directory of the file --" + file. getParent (); 17 System. out. println ("last modification time of the file path (MS) --" + file. lastModified (); 18 19 // convert millisecond to date 20 long time = file. lastModified (); 21 Date date = new Date (time); 22 SimpleDateFormat dateFormat = new SimpleDateFormat ("yyyy-MM-dd HH: mm: ss"); 23 System. out. println ("last modification time of the file path (MS) --" + dateFormat. format (date); 24 25} else {26 System. out. println ("nonexistent"); 27} 28 29}

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(5) File Operations

1 // folder operation 2 static int sumByte = 0; 3 public static void test5 () {4 5 // [1] gets the drive letter and returns an array (new is not required) 6 File [] fileRoots = File. listRoots (); 7 for (File fileRoot: fileRoots) {8 System. out. println ("Local disk:" + fileRoot); 9} 10 11 // [2] Get the array of all files in the folder 12 // (1) create path 13 File filePath = new File ("E: \ IT Learning Outline"); 14 15 // (2) put the files and folders in the path into the File class array. 16 File [] files = filePath. listFiles (); 17 18 System. out. println ("IT outline:"); 19 // (3) Traverse the File array 20 for (File file1Child: files) {21 22 // (4). If it is determined as a folder, print it directly, if it is a file, print the name and calculate the size of 23 if (file1Child. isDirectory () {24 System. out. println ("\ n --" + file1Child. getName (); 25 26 // (5) nested traversal. [You can also use recursive calling to traverse files or folders at the next level at a layer.] 27 File [] file2 = file1Child. listFiles (); 28 for (File file2Child: file2) {29 if (file2Child. isDirectory () {30 31 System. out. println ("--" + file2Child. getName (); 32 33 // (6) 34 File [] file3 = file2Child. listFiles (); 35 for (File file3Child: file3) {36 if (file3Child. isDirectory () {37 System. out. println ("--" + file3Child. getName (); 38 39} else {40 System. out. println ("-->" + file3Child. getName () + "\ t" + file3Child. length () + "bt"); 41 sumByte + = file3Child. length (); 42} 43 44} 45} else {46 System. out. println ("-->" + file2Child. getName () + "\ t" + file2Child. length () + "bt"); 47 sumByte + = file2Child. length (); 48} 49 50} 51 52} else {53 System. out. println ("-->" + file1Child. getName () + "\ t" + file1Child. length () + "bt"); 54 sumByte + = file1Child. length (); 55} 56} 57 58 System. out. println ("total file capacity:" + sumByte); 59 60} 61 62 63 // [3] You need to define an interface class 64 public static void test6 () {65 File file = new File ("E: \ IT Learning Outline"); 66 System. out. println (file. exists (); 67 String [] strings = file. list (new MyFilter (); 68 69 for (String string: strings) {70 System. out. println (string ); 71} 72} 73 74 // find the File filter 75 // class MyFilter implements FilenameFilter {76 // 77 // @ Override78 // public boolean accept (File dir, String name) {79 // TODO Auto-generated method stub80 // 81 // set the filtering idea (Here we compare the suffix Java) 82 // (1) method 1 83 /// name = name. substring (name. lastIndexOf (". "); 84 // return ". java ". equals (name); 85 // 86 // (2) method 2 87 // return name. contains ("java"); 88 // 89 // (3) method 3 90 // return name. endsWith ("java"); 91 //} 92 //} 93

Momo said: Data is permanently stored locally, and stored to a disk as a file About the directory delimiter: Directory Separator on Windows: \ On Linux: "/" Note: On windows, "\" and "/" can both be used as Directory separators, If "\" is used, the directory separator is "\". If you use "/", the separator is "/".