Prerequisites : File class
Given a main directory/folder, list all the files from it and if this directory have other nested sub-directories, list files from them also.
It is quite easy to observe simple recursion pattern in above problem.
Recursive Algorithm :
1. Create File object for main directory. 2. Get array of files for main directory. 3. If array[i] is a file : -> Print out file name. 4. If array[i] is a directory : -> Print out directory name. -> Get array of files for current sub-directory. -> Repeat the step 3 and 4 with current sub-directory. 5. Repeat the step 3 and 4 with next array[i].
// Recursive Java program to print all files // in a folder(and sub-folders) import java.io.File; public class GFG { static void RecursivePrint(File[] arr, int index, int level) { // terminate condition if (index == arr.length) return ; // tabs for internal levels for ( int i = 0 ; i < level; i++) System.out.print( "\t" ); // for files if (arr[index].isFile()) System.out.println(arr[index].getName()); // for sub-directories else if (arr[index].isDirectory()) { System.out.println( "[" + arr[index].getName() + "]" ); // recursion for sub-directories RecursivePrint(arr[index].listFiles(), 0 , level + 1 ); } // recursion for main directory RecursivePrint(arr,++index, level); } // Driver Method public static void main(String[] args) { // Provide full path for directory(change accordingly) String maindirpath = "C:\\Users\\Gaurav Miglani\\Desktop\\Test" ; // File object File maindir = new File(maindirpath); if (maindir.exists() && maindir.isDirectory()) { // array for files and sub-directories // of directory pointed by maindir File arr[] = maindir.listFiles(); System.out.println( "**********************************************" ); System.out.println( "Files from main directory : " + maindir); System.out.println( "**********************************************" ); // Calling recursive method RecursivePrint(arr, 0 , 0 ); } } } |
Output:
********************************************** Files from main directory : C:\Users\Gaurav Miglani\Desktop\Test ********************************************** Cormen.pdf Extra-Items.pdf XYZ.pdf [Docs] A.docx B.doc C.docx ABC.pdf JKL.pdf [sheets] XXX.csv YYY.csv results.pdf [Resumes] [Before2016] Resume2015.doc Resume2016.doc [Before2014] Resume2014.doc Resume2017.doc Resume2017.pdf QA.doc Testing.pdf
Below is another recursive program. Here we use recursion only for nested sub-directories. For main directory files, we use foreach loop.
// Recursive Java program to print all files // in a folder(and sub-folders) import java.io.File; public class GFG { static void RecursivePrint(File[] arr, int level) { // for-each loop for main directory files for (File f : arr) { // tabs for internal levels for ( int i = 0 ; i < level; i++) System.out.print( "\t" ); if (f.isFile()) System.out.println(f.getName()); else if (f.isDirectory()) { System.out.println( "[" + f.getName() + "]" ); // recursion for sub-directories RecursivePrint(f.listFiles(), level + 1 ); } } } // Driver Method public static void main(String[] args) { // Provide full path for directory(change accordingly) String maindirpath = "C:\\Users\\Gaurav Miglani\\Desktop\\Test" ; // File object File maindir = new File(maindirpath); if (maindir.exists() && maindir.isDirectory()) { // array for files and sub-directories // of directory pointed by maindir File arr[] = maindir.listFiles(); System.out.println( "**********************************************" ); System.out.println( "Files from main directory : " + maindir); System.out.println( "**********************************************" ); // Calling recursive method RecursivePrint(arr, 0 ); } } } |
Output:
********************************************** Files from main directory : C:\Users\Gaurav Miglani\Desktop\Test ********************************************** Cormen.pdf Extra-Items.pdf XYZ.pdf [Docs] A.docx B.doc C.docx ABC.pdf JKL.pdf [sheets] XXX.csv YYY.csv results.pdf [Resumes] [Before2016] Resume2015.doc Resume2016.doc [Before2014] Resume2014.doc Resume2017.doc Resume2017.pdf QA.doc Testing.pdf
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