返回ArrayList <file> 方法java

Question

When I compile I don't get any errors but the ArrayList<File> from the method is not getting into the main.

All the entries got added into the Folders ArrayList but it doesn't get passed into the main method.

public static ArrayList<File> Process(File aFile)
 {
  ArrayList<File> Folders = new ArrayList<File>();

  if(aFile.isFile())
  {
     String filenom = aFile.getPath();
     if (filenom.toLowerCase().endsWith(".java")){
        Folders.add(aFile);
     }
  }
  else if (aFile.isDirectory()) {
     File[] listOfFiles = aFile.listFiles();
     if(listOfFiles!=null) {
        for (int i = 0; i < listOfFiles.length; i++)
           Process(listOfFiles[i]);
     } 
     else {
        System.out.println(" [ACCESS DENIED]");
     }
  }    
  return (Folders);
}

public static void main(String[] args) throws IOException
{
  ArrayList<File> FAddress = new ArrayList<File>();
  File dir = new File("C:/");
  FAddress = Process(dir);
     if (FAddress.isEmpty())
     System.out.println("WTF?!");
  else{
     for (File fl : FAddress) {
        String FileAddress = fl.getName();
        System.out.println(FileAddress);
     }
  }
}

Answer 1

The problem is with your recursion - you correctly identify if a File object is a directory, and call Process on it:

for (int i = 0; i < listOfFiles.length; i++)
    Process(listOfFiles[i]);

But you forgot to add its result to the return value ( Folders ), so any result from subdirectories won't be added to the return value:

for (int i = 0; i < listOfFiles.length; i++)
    Folders.addAll(Process(listOfFiles[i]));

Answer 2

You create

ArrayList<File> Folders = new ArrayList<File>();

in every time when run Process. This function have recursion, so because you start at C:/ folder you never update this array.

for correct processing you should use something like:

public static ArrayList<File> Process(File aFile) {
    ArrayList<File> Folders = new ArrayList<File>();
    Process(aFile, Folders);
    return folders;
}

private static void Process(File aFile, ArrayList<File> Folders) {
    ... //your implementation without defining Folders and returning it
}

this will be usefull if you need process many levels of tree for files.

Answer 3

You can define a class level variable static ArrayList<File> Folders = new ArrayList<File>(); and then use the same for populating files.

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

public class test {
    static ArrayList<File> Folders = new ArrayList<File>();
    public static void Process(File aFile) {


        if (aFile.isFile()) {
            String filenom = aFile.getPath();
            if (filenom.toLowerCase().endsWith(".log")) {
                Folders.add(aFile);
            }
        } else if (aFile.isDirectory()) {
            File[] listOfFiles = aFile.listFiles();
            if (listOfFiles != null) {
                for (int i = 0; i < listOfFiles.length; i++)
                    Process(listOfFiles[i]);
            } else {
                System.out.println(" [ACCESS DENIED]");
            }
        }
    }

    public static void main(String[] args) throws IOException {
        File dir = new File("C:/ukba/");
        Process(dir);
        if (Folders.isEmpty())
            System.out.println("WTF?!");
        else {
            for (File fl : Folders) {
                String FileAddress = fl.getName();
                System.out.println(FileAddress);
            }
        }
        Folders = null;
    }
}