File Dialogs

The java.awt.FileDialog class is a subclass of java.awt.Dialog used for choosing a file to open or save. This class uses the host platform's standard open and save file dialogs. You won't add components to a FileDialog, or handle user interaction. You'll just retrieve the result which will be the name and directory of a file. Since an applet can't rely on having access to the file system, FileDialogs are primarily useful in applications.

There are three steps to using a FileDialog:

1. Create the FileDialog
2. Make the FileDialog visible.
3. Get the directory name and file name of the chosen file

You create a FileDialog with the constructor

public FileDialog(Frame parent, String title, int mode)

The Frame is the parent of this file dialog. This will normally be the main window of the application or the frontmost window of the application. The title argument is simply the title for the FileDialog, normally something like "Please choose the file to open:" mode is one of the two mnemonic constants FileDialog.LOAD or FileDialog.SAVE. Use FileDialog.LOAD if you want the user to choose a file to open. Use FileDialog.SAVE if you want the user to choose a file to save the data into. A typical use of this might look like

FileDialog fd = new FileDialog(new Frame(), 
 "Please choose the file to open:", FileDialog.LOAD);

Finally make the FileDialog visible the same way you make any other window visible. Just pass true to the FileDialog's setVisible() method.

fd.setVisible(true);

At this point the operating system takes over and handles user interaction until the user either chooses a file or cancels. Your program stops here and waits for the user to choose a file. When the user does choose a file, the file dialog disappears from the screen and your program resumes. You then find out what file the user chose by using the file dialog's getDirectory() and getFile() methods. Use these two strings to create a new File object. In short,

FileDialog fd = new FileDialog(new Frame(), 
 "Please choose a file:", FileDialog.LOAD);
fd.show();
if (fd.getFile() != null) {
  File f = new File(fd.getDirectory(), fd.getFile());
}

If the user cancels the save, both getDirectory() and getFile() return null. Be sure to check for this!