FileExample.java

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class FileExample {

  /*

  Given a File (which can represent either a file or directory), return a list
  of all the files in that directory and all its subdirectories.

  If given the path of a file (rather than a directory), it returns a list with
  just that element.
  
  For example, for the following structure:

  some-files/
  |-  a.txt
  |-  more-files/
      |-  b.txt
      |-  c.java
  |-  even-more-files/
      |-  d.java
      |-  a.txt

  Given new File("some-files/") as a parameter, we'd expect [some-files/a.txt,
  some-files/more-files/b.txt, some-files/more-files/c.java,
  some-files/even-more-files/d.java, some-files/even-more-files/a.txt] as results

  Given new File("some-files/more-files") as a parameter, we'd expect
  [some-files/more-files/b.txt, some-files/more-files/c.java] as results

  Given new File("some-files/a.txt") as a parameter, we'd expect
  [some-files/a.txt] and a result

  See the File documentation here: https://docs.oracle.com/javase/8/docs/api/java/io/File.html

  */


	static List<File> getFiles(File start) throws IOException {
	  File f = start;
	  List<File> result = new ArrayList<>();
    if(f.isFile()){
      result.add(f);
      return result;
    }
	  if(f.isDirectory()) {
      File[] paths = f.listFiles();
      for(File subFile: paths) {
        if(subFile.isFile())
          result.add(subFile);
        else if(subFile.isDirectory()){
          File[] paths2 = subFile.listFiles();
          
          for(File subFile2: paths2)
            result.add(subFile2);
        }
        
      }
	  }
	  return result;
	}
}