32.7. Key Terms
29.9. JFileChooser
The javax.swing.JFileChooser class displays a dialog box from which the user can navigate through the file system and select files for loading or saving, as shown in Figure 29.21.
Figure 29.21. The Swing JFileChooser shows files and directories, and enables the user to navigate through the file system visually.
Like JColorChooser , JFileChooser is a lightweight component inherited from JComponent . It can be added to any container if desired, but often you create an instance of JFileChooser and display it standalone.
JFileChooser is a subclass of JComponent . There are several ways to construct a file dialog box. The simplest is to use JFileChooser 's no-arg constructor.
The file dialog box can appear in two types: open and save. The open type is for opening a file, and the save type is for storing a file. To create an open file dialog, use the following method:
public int showOpenDialog(Component parent) This method creates a dialog box that contains an instance of JFileChooser for opening a file. The method returns an int value, either APPROVE_OPTION or CANCEL_OPTION , which indicates whether the OK button or the Cancel button was clicked.
Similarly, you can use the following method to create a dialog for saving files:
public int showSaveDialog(Component parent) The file dialog box created with showOpenDialog or showSaveDialog is modal. The JFileChooser class has the properties inherited from JComponent . It also has the following useful properties:
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dialogType specifies the type of this dialog. Use OPEN_DIALOG when you want to bring up a file chooser that the user can use to open a file. Likewise, use SAVE_DIALOG to let the user choose a file for saving.
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dialogTitle is the string that is displayed in the title bar of the dialog box.
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currentDirectory is the current directory of the file. The type of this property is java.io.File . If you want the current directory to be used, use setCurrentDirectory(new File(".")) .
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selectedFile is the file you have selected. You can use getSelectedFile() to return the selected file from the dialog box. The type of this property is java.io.File . If you have a default file name that you expect to use, use setSelectedFile(new File(filename)) .
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selectedFiles is a list of the files selected if the file chooser is set to allow multi-selection. The type of this property is File[] .
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multiSelectionEnabled is a boolean value indicating whether multiple files can be selected. By default, it is false .
Let us create an example of a simple text editor that uses Swing menus , tool bar, file chooser, and color chooser, as shown in Figure 29.22, which allows the user to open and save text files, clear text, and change the color and font of the text. Listing 29.8 shows the program.
Figure 29.22. The editor enables you to open and save text files from the File menu or from the tool bar, and to change the color and font of the text from the Edit menu.
Listing 29.8. TextEditor.java
(This item is displayed on pages 995 - 998 in the print version)
1 import java.io.*; 2 import java.awt.*; 3 import java.awt.event.*; 4 import javax.swing.*; 5 6 public class TextEditor extends JApplet { 7 // Declare and create image icons 8 private ImageIcon openImageIcon = 9 new ImageIcon(getClass().getResource( "image/open.gif" )); 10 private ImageIcon saveImageIcon = 11 new ImageIcon(getClass().getResource( "image/save.gif" )); 12 13 // Create menu items 14 private JMenuItem jmiOpen = new JMenuItem( "Open" , openImageIcon); 15 private JMenuItem jmiSave = new JMenuItem( "Save" , saveImageIcon); 16 private JMenuItem jmiClear = new JMenuItem( "Clear" ); 17 private JMenuItem jmiExit = new JMenuItem( "Exit" ); 18 private JMenuItem jmiForeground = new JMenuItem( "Foreground" ); 19 private JMenuItem jmiBackground = new JMenuItem( "Background" ); 20 21 // Create buttons to be placed in a tool bar 22 private JButton jbtOpen = new JButton(openImageIcon); 23 private JButton jbtSave = new JButton(saveImageIcon); 24 private JLabel jlblStatus = new JLabel(); 25 26 // Create a JFileChooser with the current directory 27 private JFileChooser jFileChooser1 28 = new JFileChooser( new File( "." )); 29 30 // Create a text area 31 private JTextArea jta = new JTextArea(); 32 33 public TextEditor() { 34 // Add menu items to the menu 35 JMenu jMenu1 = new JMenu( "File" ); 36 jMenu1.add(jmiOpen); 37 jMenu1.add(jmiSave); 38 jMenu1.add(jmiClear); 39 jMenu1.addSeparator(); 40 jMenu1.add(jmiExit); 41 42 // Add menu items to the menu 43 JMenu jMenu2 = new JMenu( "Edit" ); 44 jMenu2.add(jmiForeground); 45 jMenu2.add(jmiBackground); 46 47 // Add menus to the menu bar 48 JMenuBar jMenuBar1 = new JMenuBar(); 49 jMenuBar1.add(jMenu1); 50 jMenuBar1.add(jMenu2); 51 52 // Set the menu bar 53 setJMenuBar(jMenuBar1); 54 55 // Create tool bar 56 JToolBar jToolBar1 = new JToolBar(); 57 jToolBar1.add(jbtOpen); 58 jToolBar1.add(jbtSave); 59 60 jmiOpen.addActionListener( new ActionListener() { 61 public void actionPerformed(ActionEvent e) { 62 open(); 63 } 64 }); 65 66 jmiSave.addActionListener( new ActionListener() { 67 public void actionPerformed(ActionEvent evt) { 68 save(); 69 } 70 }); 71 72 jmiClear.addActionListener( new ActionListener() { 73 public void actionPerformed(ActionEvent evt) { 74 jta.setText( null ); 75 } 76 }); 77 78 jmiExit.addActionListener( new ActionListener() { 79 public void actionPerformed(ActionEvent evt) { 80 System.exit( ); 81 } 82 }); 83 84 jmiForeground.addActionListener( new ActionListener() { 85 public void actionPerformed(ActionEvent evt) { 86 Color selectedColor = 87 JColorChooser.showDialog( null , "Choose Foreground Color" , 88 jta.getForeground()); 89 90 if (selectedColor != null ) 91 jta.setForeground(selectedColor); 92 } 93 }); 94 95 jmiBackground.addActionListener( new ActionListener() { 96 public void actionPerformed(ActionEvent evt) { 97 Color selectedColor = 98 JColorChooser.showDialog( null , "Choose Background Color" , 99 jta.getForeground()); 100 101 if (selectedColor != null ) 102 jta.setBackground(selectedColor); 103 } 104 }); 105 106 jbtOpen.addActionListener( new ActionListener() { 107 public void actionPerformed(ActionEvent evt) { 108 open(); 109 } 110 }); 111 112 jbtSave.addActionListener( new ActionListener() { 113 public void actionPerformed(ActionEvent evt) { 114 save(); 115 } 116 }); 117 118 add(jToolBar1, BorderLayout.NORTH); 119 add(jlblStatus, BorderLayout.SOUTH); 120 add( new JScrollPane(jta), BorderLayout.CENTER); 121 } 122 123 /** Open file */ 124 private void open() { 125 if ( jFileChooser1.showOpenDialog( this ) == 126 JFileChooser.APPROVE_OPTION ) 127 open(jFileChooser1.getSelectedFile()); 128 } 129 130 /** Open file with the specified File instance */ 131 private void open(File file) { 132 try { 133 // Read from the specified file and store it in jta 134 BufferedInputStream in = new BufferedInputStream( 135 new FileInputStream(file)); 136 byte [] b = new byte [in.available()]; 137 in.read(b, , b.length); 138 jta.append( new String(b, , b.length)); 139 in.close(); 140 141 // Display the status of the Open file operation in jlblStatus 142 jlblStatus.setText(file.getName() + " Opened" ); 143 } 144 catch (IOException ex) { 145 jlblStatus.setText( "Error opening " + file.getName()); 146 } 147 } 148 149 /** Save file */ 150 private void save() { 151 if ( jFileChooser1.showSaveDialog( this ) == 152 JFileChooser.APPROVE_OPTION ) { 153 save(jFileChooser1.getSelectedFile()); 154 } 155 } 156 157 /** Save file with specified File instance */ 158 private void save(File file) { 159 try { 160 // Write the text in jta to the specified file 161 BufferedOutputStream out = new BufferedOutputStream( 162 new FileOutputStream(file)); 163 byte [] b = (jta.getText()).getBytes(); 164 out.write(b, , b.length); 165 out.close(); 166 167 // Display the status of the save file operation in jlblStatus 168 jlblStatus.setText(file.getName() + " Saved " ); 169 } 170 catch (IOException ex) { 171 jlblStatus.setText( "Error saving " + file.getName()); 172 } 173 } 174 } |
The program creates the File and Edit menus (lines 34 “45). The File menu contains the menu commands Open for loading a file, Save for saving a file, Clear for clearing the text editor, and Exit for terminating the program. The Edit menu contains the menu commands Foreground Color and Background Color for setting foreground color and background color in the text. The Open and Save menu commands can also be accessed from the tool bar, which is created in lines 56 “58. The status of executing Open and Save is displayed in the status label, which is created in line 24.
jFileChooser1 , an instance of JfileChooser , is created for displaying the file dialog box to open and save files (lines 27 “28). new File(".") is used to set the current directory to the directory where the class is stored.
The open method is invoked when the user clicks the Open menu command or the Open tool bar button (lines 62, 108). The showOpenDialog method (line 125) displays an Open dialog box, as shown in Figure 29.21. Upon receiving the selected file, the method open(file) (line 127) is invoked to load the file to the text area using a BufferedInputStream wrapped on a FileInputStream .
The save method is invoked when the user clicks the Save menu command or the Save tool bar button (lines 68, 114). The showSaveDialog method (line 151) displays a Save dialog box. Upon receiving the selected file, the method save(file) (line 153) is invoked to save the contents from the text area to the file using a BufferedOutputStream wrapped on a FileOutputStream .
The color dialog is displayed using the static method showDialog (lines 87, 98) of JColorChooser . Thus you don't need to create an instance of JFileChooser . The showDialog method returns the selected color if the OK button is clicked after a color is selected.
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