Tutorials : Working with files and directories in Java :

The MyDir class

The class for the directory is also rather simple, but this class also has to keep track of the files and directories it contains. Let's use two Vectors for this purpose. Since the code is so simple I'll omit most of the comments to save some space.

package hansen.playground;
import java.util.*;

public class MyDir {
  private String path;
  private String name;
   // All files in this directory:
  private Vector files = new Vector();
   // All directories in this directory:
  private Vector dirs = new Vector();

  public MyDir(String path, String name) {
    this.path = path;
    this.name = name;
  }  
  
  public String getName() { return name; }  

  public String getPath() { return path; }  
  
  public void addFile(MyFile f) { files.addElement(f); }  

  public void addDir(MyDir d) { dirs.addElement(d); }  
  
  public Vector getFiles() { return files; }  
  
  public Vector getDirs() { return dirs; }  
  
}

A helper class: MyFileStructure

With these two classes we're now ready to build our own directory tree. A helper JavaBeans, MyFileStructure, is used for this. In its first version--we'll enhance it as we proceed--it only has two member variables:

dirname - which holds the name of the top directory whose contents we'll find
mdir - is the resulting "top-MyDir", holding the complete directory structure.

The recursive method is called "build", and it has as a parameter a File object for a directory. Note that "build" will return a null if it receives an invalid directory. MyFileStructure looks like this in version 1:

package hansen.playground;
import java.io.*;

public class MyFileStructure{ 
  private String dirname;
  private MyDir mdir;

  public void setDirname(String dirname) {
    this.dirname = dirname;
  }
  
  /*
  * Build a hierarchy of MyDir's and 
  * MyFile's for this directory
  */
  public void build() {
    File f = new File(dirname);
    mdir = build(f);
  }  

  /*
  * Build a hierarchy of MyDir's and 
  * MyFile's for "f"
  */
  private MyDir build(File f) { 
    if (!f.exists()) return null; 
    if (!f.isDirectory()) return null; 
    
    // f is an existing directory
    String path = f.getPath();
    String name = f.getName();
    MyDir mdir = new MyDir(path, name);

    // Loop thru files and directories in this path
    String[] files = f.list();
    for (int i = 0; i < files.length; i++) {
      File f2 = new File(path, files[i]);
      if (f2.isFile()) {
        mdir.addFile(new MyFile(path, files[i]));
      } else if (f2.isDirectory()) {
        File f3 = new File(path, files[i]);
        MyDir m = build(f3); // recursive call
        if (m != null) { mdir.addDir(m); }  
      }
    }
    return mdir;
  }  

}

The first test program

To test our classes we only need a simple test program as illustrated below. It is run from a command line and the name of the directory is given as a parameter:

package hansen.playground;

public class Test1 {  
  public static void main(String[] args) {
    if (args.length != 0) {
      MyFileStructure mf = new MyFileStructure();
      mf.setDirname(args[0]);
      mf.build();
      mf.list();
    }  
  } 
}

I have added a call to a "list" method, because otherwise we'll get no results from the program. The reason for this is of course, that we have only created the directory tree in the member variable "mdir", so we need to add some code for displaying the tree. This is done with the "list" method in MyFileStructure, and again a recursive method will help us do the coding:

  public void list() {
    if (mdir == null) {
      System.out.println("Not a valid directory");
      return;
    }  
    System.out.println("Dir: " + mdir.getPath());
    list(mdir);
  }
  
  public void list(MyDir m) {
    // First list the directories 
    Vector md = m.getDirs();
    for (int i = 0; i < md.size(); i++) {
      MyDir d = (MyDir)md.elementAt(i);
      System.out.println("Dir: " + d.getPath());
      list(d); // recursive call
    }  
    // And now list the files 
    Vector mf = m.getFiles();
    for (int i = 0; i < mf.size(); i++) {
      MyFile f = (MyFile)mf.elementAt(i);
      System.out.println("File: " + 
	f.getPath() + File.separator + f.getName());
    }  
  }

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