The javax.swing.JFileChooser
class
is used to create file choosers for selecting files or directories
to open or save.
The sample code below uses JFileChooser in the Open button action listener.
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// File : filechooser/CountWords.java // Purpose: Counts words in file. Illustrates JFileChooser. // Java 5: Scanner. // Author : Fred Swartz // Date : 2005-02-23 import java.awt.*; import java.awt.event.*; import javax.swing.*; import java.io.*; import java.util.*; //////////////////////////////////////////////////////// main class public class CountWords { public static void main(String[] args) { JFrame window = new JFrame("Count Words"); window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); window.setContentPane(new CountWordsGUI()); window.pack(); window.setVisible(true); } } ////////////////////////////////////////////////////// CountWordsGUI class CountWordsGUI extends JPanel { //... Instance variables JTextField m_fileNameTF = new JTextField(15); JTextField m_wordCountTF = new JTextField(4); JFileChooser m_fileChooser = new JFileChooser(); //================================================== constructor CountWordsGUI() { m_fileNameTF.setEditable(false); m_wordCountTF.setEditable(false); JButton openButton = new JButton("Open"); //... Add listeners openButton.addActionListener(new OpenAction()); //... Layout components setLayout(new FlowLayout()); add(openButton); add(m_fileNameTF); add(new JLabel("Word Count")); add(m_wordCountTF); } //================================================== processFile private int countWordsInFile(File f) { int numberOfWords = 0; // For counting words. try { Scanner wordScanner = new Scanner(f); wordScanner.useDelimiter("[^A-Za-z]+"); while (wordScanner.hasNext()) { String word = wordScanner.next(); numberOfWords++; } } catch (FileNotFoundException fnfex) { JOptionPane.showMessageDialog(CountWordsGUI.this, "You gave me an unreadable file"); } return numberOfWords; } //////////////////////////////////////////// Open button listener class OpenAction implements ActionListener { public void actionPerformed(ActionEvent ae) { //... Open a file dialog. int retval = m_fileChooser.showOpenDialog(CountWordsGUI.this); if (retval == JFileChooser.APPROVE_OPTION) { //... The user selected a file, process it. File file = m_fileChooser.getSelectedFile(); countWordsInFile(file); //... Update user interface. m_fileNameTF.setText(file.getName()); m_wordCountTF.setText("" + countWordsInFile(file)); } } } } |
Use one of three methods to display the dialog after it has been created.
r = fc.showOpenDialog(owner); // button labeled "Open" r = fc.showSaveDialog(owner); // button labeled "Save" r = fc.showDialog(owner, title);
The owner parameter is the component (eg, JFrame, JPanel, ...) over which
the dialog should be centered.
You can use null
for the owner, which will put the dialog
in the center of the screen. To get the enclosing class's instance, as
in this example, write the enclosing class name followed by ".this".
The title parameter is a string that is used as the dialog's title
and accept button text.
The user may either select a file or directory, or click CANCEL
or close the file chooser window. If the user selected a file
or directory, the value returned will be JFileChooser.APPROVE_OPTION
.
Always check this value. For example,
int retval = fc.showOpenDialog(null); if (retval == JFileChooser.APPROVE_OPTION) { . . . // The user did select a file.;
After checking for JFileChooser.APPROVE_OPTION
,
the File
value of the selection is returned
from a call on getSelectedFile
.
int retval = fc.showOpenDialog(null);
if (retval == JFileChooser.APPROVE_OPTION) {
File myFile = fc.getSelectedFile();
// DO YOUR PROCESSING HERE. OPEN FILE OR ...
}
Altho a new file chooser can be created inside a listener, there are advantages to creating it once outside and reusing it.
By default a file chooser allows the user to select only files. To allow selection of either files or directories, or only directories, use one of the following calls.
fc.setFileSelectionMode(JFileChooser.FILES_ONLY); // default fc.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY); fc.setFileSelectionMode(JFileChooser.FILES_AND_DIRECTORIES);
You can specify the kinds of files that should be shown (eg,
with a specific extension, ...), but supplying a JFileFilter
.
myChooser.setFileFilter(FileFilter filter);
See FileFilter. [NEEDS MORE WORK]
The file chooser will start the file dialog at some default
directory, for example, "C:\My Documents
".
To start the dialog at a different directory (called the
current directory), specify the
directory path as a String
or File
value in the
JFileChooser
constructor.
JFileChooser m_fileChooser = new JFileChooser("C:\home");
The current directory is ".".
Portability warning: If you put system specific file paths in your code, the program will not be portable to other systems. Note that the above call is therefore not portable.