Tutorials : Java Tutorial: Working with files and directories in Java Part 2 :

Graphics

To make a nice, graphical view we'll need some graphics elements to put inside <img> HTML-tags. It's like collecting a jig saw puzzle. If you look at figure 1 then you'll see that we only need these 6 pieces:

I have made two directory images - since we'll soon implement an open/close-directory function in our application. As you can see I've dropped the plus/minus-signs on the directory-pictures to simplify things a bit.

The pictures are made with a simple graphics utility (like Paint Shop Pro) using a few screen dumps with FrontPage pages. Be prepared to use some time to get the size of the pictures right -- if you don't simply use mine from the zip-file. Now it's simply a matter of putting these pieces together to make a directory structure. To show you how it works let's create figure 1 (without the text). The border of each picture has been made visible to show how it's done:

To make the graphics view we'll have to code a new version of MyFileStructure - the class that builds the output. A couple of notes about how this is done:

1. the "level", which is one of the parameters to the methods in MyFileStructure, is used to determine how many of the vertical lines to place first. If level=4 then you get this result:
   
2. in front of a file or folder we must place an "e-bar" or "t-bar". The "e-bar" is used if the file or folder is the last in its directory
3. the very first folder doesn't have any bar in front of it.
4. to determine if one uses an open or closed folder we must add a new parameter to the methods in MyFileStructure.

The "Explorer" class

The new class -- called MyFileStructureExplorer (since it has a Windows File Explorer look) -- may be coded like this:

package hansen.playground;

public class MyFileStructureExplorer extends MyFileStructure {

  protected void outFile(MyFile f, int level, boolean last) {
    String name = f.getName();
    String horizontalGif = (last) ? imageTag("ebar") : imageTag("tbar");
    String fileGif = horizontalGif + imageTag("file");
    result += verticalGifs(level-2) + fileGif + " " + name + "<br>\n";
  }  
  
  protected void outDir(MyDir d, int level, boolean open, boolean last) {
    String name = d.getName();
    int key = d.getKey(); 
    String folderGif;
    if (open) {
      folderGif = "open";
    } else {
      folderGif = "closed";
    }
    // Show image of a directory
    folderGif = "<img src=\"images/" + folderGif + 
                ".gif\" border=0 align=center>";
    // If not first directory then show a "branch" before the directory 
    String horizontalGif = "";
    if (level > 1) 
      horizontalGif = (last) ? imageTag("ebar") : imageTag("tbar");
    // Put a link around the directory image
    folderGif = horizontalGif + "<a href=\"#\" onclick=\"toggle(" + key + 
                ")\">" + folderGif + "</a>";
    result += verticalGifs(level-2) + folderGif + " " + name + "<br>\n";
  }  
  
  /*
  * Return "n" vertical-bar Gifs  
  */
  private String verticalGifs(int n) {
    String s = "";
    for (int i=0; i < n; i++) {
      s += imageTag("vbar");
    }
    return s;
  }  
  
  /*
  * Return an IMG-tag
  */
  private String imageTag(String name) {
    return "<img src=\"images/" + name + ".gif\" align=center>"; 
  }  
  
}

Since the outFile and outDir methods now have a couple of new parameters we also need to update the base class MyFileStructure. The code can be seen in the zip-file.

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