Develop Reference

Strange error with Drag and Drop in AWT in Java

Allright here is the error: java.awt.dnd.InvalidDnDOperationException: The operation requested cannot be performed by the DnD system since it is not in the appropriate state. The error appears when I drop some File inside the program (grabbed from the desktop). I am using Ubuntu 16.04 with Nautilus.
import javax.swing.*;
import java.awt.datatransfer.DataFlavor;
import java.awt.dnd.*;
import java.io.File;
import java.util.List;
class UI extends JFrame {
List<File> droppedFiles;
UI(){
super("My Program");
this.setDefaultCloseOperation(EXIT_ON_CLOSE);
this.setLayout(null);
this.setVisible(true);
this.setResizable(true);
this.setSize(800, 500);
this.setExtendedState(MAXIMIZED_BOTH);
JTextField dropArea = getDropArea();
this.add(dropArea);
}
private JTextField getDropArea(){
JTextField dropArea = new JTextField("Drop file here");
dropArea.setBounds(50, 50, 200, 200);
dropArea.setDropTarget(createNewDropTarget(dropArea));
return dropArea;
}
private DropTarget createNewDropTarget(JTextField dropArea) {
DropTarget dt = new DropTarget(){
#Override
public synchronized void drop(DropTargetDropEvent dtde) {
super.drop(dtde);
try {
dtde.acceptDrop(DnDConstants.ACTION_COPY);
droppedFiles = (List<File>) dtde.getTransferable().
getTransferData(DataFlavor.javaFileListFlavor);
dropArea.setText(droppedFiles.get(0).getName());
}catch (Exception e){
e.printStackTrace();
}
}
};
return dt;
}
}
The Error appears on the line where droppedFiles is initialized. (in the try catch block).

In a way you set up DropTarget there is no need to call super.drop(dtde);. This is actually the reason for the exception. Here is the implementation of DropTarget.drop():
public synchronized void drop(DropTargetDropEvent dtde) {
clearAutoscroll();
if (dtListener != null && active)
dtListener.drop(dtde);
else { // we should'nt get here ...
dtde.rejectDrop();
}
}
Since you are not initializing DropTarget with a listener the drop is rejected, and the subsequent call getTransferable() fails with InvalidDnDOperationException. If you comment super.drop(dtde); the problem should go away. A cleaner alternative would be to create a listener and pass it to DropTarget. Here is a small example:
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.datatransfer.DataFlavor;
import java.awt.dnd.DnDConstants;
import java.awt.dnd.DropTarget;
import java.awt.dnd.DropTargetAdapter;
import java.awt.dnd.DropTargetDropEvent;
import java.io.File;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class DDTest extends JPanel {
public DDTest() {
setLayout(new BorderLayout());
final JTextField dropArea = new JTextField("Drop file here");
add(dropArea);
new DropTarget(dropArea, new DropTargetAdapter() {
#Override
public void drop(DropTargetDropEvent dtde) {
try {
dtde.acceptDrop(DnDConstants.ACTION_COPY);
List<File> droppedFiles = (List<File>) dtde
.getTransferable().getTransferData(
DataFlavor.javaFileListFlavor);
dropArea.setText(droppedFiles.get(0).getName());
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
#Override
public Dimension getPreferredSize() {
return new Dimension(300, 200);
}
private static void createAndShowGUI() {
final JFrame frame = new JFrame("DDTest");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new DDTest());
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}
PS:
Note that using absolute layout can be complex and usually can be avoided. See A Visual Guide to Layout Managers for some ideas.

Swing - Change menu bar and menu items font size in runtime

as title says, I need to change the font size of the menu bar and every item on it (and also the items of the ite,s) using SWING.
I have the following code which works but not on runtime, I need it to be when clicking on a menu item
Font f = new Font("sans-serif", Font.PLAIN, 12);
UIManager.put("Menu.font", f);
UIManager.put("MenuItem.font", f);
And the code I have for my menu is
private class foo{
private JMenu mnArchivo;
private JMenuBar menuBar;
menuBar = new JMenuBar();
frmAdministracinHospital.setJMenuBar(menuBar);
JRadioButtonMenuItem rdbtnmntmGrande = new JRadioButtonMenuItem("Grande");
rdbtnmntmGrande.addActionListener(new MiGrandeActionListener());
rdbtnmntmGrande.setIcon(new ImageIcon(PrincipalWindow.class.getResource("/presentacion/fontbig.png")));
buttonGroup.add(rdbtnmntmGrande);
mnTamanoFuente.add(rdbtnmntmGrande);
private class MiGrandeActionListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
Font f = new Font(menuBar.getFont().getFontName(), menuBar.getFont().getStyle(), 12);
UIManager.put("Menu.font", f);
}
}
I haven't found any similar question which does it on run time, how could I achieve this?
EDIT. CODE ADD WITH NO WORKING THE FONT SIZE CHANGE MORE THAN ONCE.
package presentacion;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.SystemColor;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ButtonGroup;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JPanel;
import javax.swing.JRadioButtonMenuItem;
import javax.swing.JTabbedPane;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import dominio.Appointment;
import dominio.Patient;
import dominio.Specialist;
public class pepe {
private JFrame a;
private JTabbedPane tabbedPane;
private JMenuBar menuBar;
private final ButtonGroup buttonGroup = new ButtonGroup();
public pepe() {
initialize();
a.setVisible(true);
}
public static void main(String[] args) {
try {
// Set System L&F
UIManager.setLookAndFeel(
UIManager.getSystemLookAndFeelClassName());
}
catch (UnsupportedLookAndFeelException e) {
// handle exception
}
catch (ClassNotFoundException e) {
// handle exception
}
catch (InstantiationException e) {
// handle exception
}
catch (IllegalAccessException e) {
// handle exception
}
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
pepe window = new pepe();
window.a.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
private void initialize() {
a = new JFrame();
a.setTitle("Administraci\u00F3n Hospital");
a.setBounds(100, 100, 1195, 710);
a.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
tabbedPane = new JTabbedPane(JTabbedPane.TOP);
tabbedPane.setBackground(SystemColor.info);
menuBar = new JMenuBar();
a.setJMenuBar(menuBar);
JMenu mnVer = new JMenu("Ver");
menuBar.add(mnVer);
JMenu mnTamanoFuente = new JMenu("Tama\u00F1o fuente");
mnVer.add(mnTamanoFuente);
JRadioButtonMenuItem rdbtnmntmPequeo = new JRadioButtonMenuItem("Peque\u00F1o");
rdbtnmntmPequeo.addActionListener(new MiPequenaActionListener());
buttonGroup.add(rdbtnmntmPequeo);
mnTamanoFuente.add(rdbtnmntmPequeo);
JRadioButtonMenuItem rdbtnmntmGrande = new JRadioButtonMenuItem("Grande");
rdbtnmntmGrande.addActionListener(new MiGrandeActionListener());
buttonGroup.add(rdbtnmntmGrande);
mnTamanoFuente.add(rdbtnmntmGrande);
}
private class MiPequenaActionListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
Font f = new Font(a.getFont().getFontName(), a.getFont().getStyle(), 10);
UIManager.put("Label.font", f);
UIManager.put("Menu.font", f);
UIManager.put("MenuItem.font", f);
SwingUtilities.updateComponentTreeUI(a);
}
}
private class MiGrandeActionListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
Font f = new Font(a.getFont().getFontName(), a.getFont().getStyle(), 13);
UIManager.put("Label.font", f);
UIManager.put("Menu.font", f);
UIManager.put("MenuItem.font", f);
SwingUtilities.updateComponentTreeUI(a);
}
}
}
With this it lets me change the font size just once, to big for example (grande) if then I click on small or normal it wont do anything.
Thank you.

I have the following code which works but not on runtime,
Font f = new Font(menuBar.getFont().getFontName(), menuBar.getFont().getStyle(), 12);
UIManager.put("Menu.font", f);
Basically you need to do a LAF change, so the above should be:
Font f = new FontUIResource(menuBar.getFont().getFontName(), menuBar.getFont().getStyle(), 12);
UIManager.put("Menu.font", f);
SwingUtilities.updateComponentTreeUI(frame);
You need to make sure the Font is a FontUIResource so the LAF can change the property.
Read the section from the Swing tutorial on Changing the LAF After Startup for more information and examples.

Clipboard listener in java [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 5 years ago.
I am trying to write a simple program to listen to clipboard copys and save them.
I wrote the following code:
package CopyPaste;
import javax.swing.JFrame;
public class Main {
public static void main(String[] args){
JFrame frame = new JFrame("Copy Paste");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(600,600);
frame.setLocationRelativeTo(null);
MyPanel pane = new MyPanel();
frame.add(pane);
frame.setVisible(true);
}
}
package CopyPaste;
import java.awt.BorderLayout;
import java.awt.Font;
import java.awt.TextArea;
import java.awt.Toolkit;
import java.awt.datatransfer.Clipboard;
import java.awt.datatransfer.ClipboardOwner;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.FlavorEvent;
import java.awt.datatransfer.FlavorListener;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.io.IOException;
import java.lang.Object;
import javax.swing.JButton;
import javax.swing.JPanel;
public class MyPanel extends JPanel implements ClipboardOwner{
private final static Font f = new Font("david", Font.BOLD,22);
private static TextArea text;
private JButton btnGet;
private Clipboard c;
public MyPanel(){
this.setLayout(new BorderLayout());
text = new TextArea();
text.setFont(f);
add(BorderLayout.CENTER,text);
add(BorderLayout.SOUTH,this.getSouthButton());
c.addFlavorListener(new FlavorListener() {
#Override
public void flavorsChanged(FlavorEvent e) {
proccessClipboard(c);
}
});
}
private static void proccessClipboard(Clipboard c){
String s = null;
c = Toolkit.getDefaultToolkit().getSystemClipboard();
try {
s = (String) c.getContents(null).getTransferData(DataFlavor.stringFlavor);
} catch (UnsupportedFlavorException | IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
text.setText(s);
}
//return the south panel button
private JPanel getSouthButton(){
JPanel south = new JPanel();
btnGet = new JButton("Get");
ButtonLis lis = new ButtonLis();
btnGet.addActionListener(lis);
south.add(btnGet);
return south;
}
private class ButtonLis implements ActionListener{
public void actionPerformed(ActionEvent e) {
String s = null;
if (e.getSource()==btnGet){
c = Toolkit.getDefaultToolkit().getSystemClipboard();
try {
s = (String) c.getContents(null).getTransferData(DataFlavor.stringFlavor);
} catch (UnsupportedFlavorException | IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
text.setText(s);
}
}
}
#Override
public void lostOwnership(Clipboard clipboard, Transferable contents) {
// TODO Auto-generated method stub
}
}
error:
Exception in thread "main" java.lang.NullPointerException
at CopyPaste.MyPanel.<init>(MyPanel.java:39)
at CopyPaste.Main.main(Main.java:13)
for some reason the eclipse don't show any errors but when i hit the "run" button i get some compile error.
someone know what can cause this?

This is an old post, but I am going to answer it for other people who search same thing. The right way is to initialize the Clipboard before define the FlavourListener. So "MyPanel" constructor has to be updated right this:
public MyPanel(){
this.setLayout(new BorderLayout());
text = new TextArea();
text.setFont(f);
add(BorderLayout.CENTER,text);
add(BorderLayout.SOUTH,this.getSouthButton());
c = Toolkit.getDefaultToolkit().getSystemClipboard();
c.addFlavorListener(new FlavorListener() {
#Override
public void flavorsChanged(FlavorEvent e) {
proccessClipboard(c);
}
});
}

Your error is occurring at line 39 of your Panel class as this line from your error message is telling you:
at CopyPaste.MyPanel.<init>(MyPanel.java:39)
Which is this line:
c.addFlavorListener(new FlavorListener() {
So, your clipboard variable, c, is null when you try to add a FlavorListener to it, and it must be initialized before you try to use it.

SwingWorker Process() warning

I tried to write a simple test program using Swing, all I want to do is load a text file and display the path of the chosen text file in a text area. I keep getting a warning on the process method "never used locally" and it is not appending any text to the textbox. Maybe I'm misunderstanding something, I hope someone can help me.
code:
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.SwingWorker;
import javax.swing.filechooser.FileNameExtensionFilter;
public class MyPanel3 extends JPanel{
/**
*
*/
private static final long serialVersionUID = 1L;
private JTextArea jcomp;
private JButton btn;
private String testfile;
public MyPanel3() {
//construct components
jcomp = new JTextArea (1, 1);
jcomp.setBorder(BorderFactory.createDashedBorder(Color.BLACK));
btn = new JButton ("open");
//adjust size and set layout
setPreferredSize (new Dimension (944, 575));
BoxLayout layout = new BoxLayout (this, BoxLayout.Y_AXIS);
setLayout(layout);
//add main components
add (jcomp);
add (btn);
new SwingWorker<Void, String>(){
protected Void doInBackground(){
//do processes...
btn.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
final JFileChooser chooseFile = new JFileChooser();
FileNameExtensionFilter filter = new FileNameExtensionFilter(".txt","txt");
chooseFile.setFileFilter(filter);
chooseFile.setAcceptAllFileFilterUsed(false);
chooseFile.setMultiSelectionEnabled(true);
if(ae.getSource().equals(btn))
{
System.out.println("do in background running");
int returnVal = chooseFile.showOpenDialog(MyPanel3.this);
if(returnVal == JFileChooser.APPROVE_OPTION)
{
File[] files = chooseFile.getSelectedFiles();
testfile = files[0].getPath();
publish(testfile);
}
}
}
});
return null;
}
protected void process(String s) {
jcomp.append(s);
}
protected void done() {
try
{
//System.out.println("The operation was completed");
}
catch (Exception e)
{
e.printStackTrace();
}
}
}.execute();
}
public static void main(String[] args){
JFrame frame = new JFrame ("MyTest");
frame.getContentPane();
frame.add(new MyPanel3());
frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setVisible (true);
}
}
warning reads:
The method process(String) from the type new
SwingWorker(){} is never used locally
EDIT:
with help from MadProgrammer, program is now working (selecting 3 files and printing the paths as strings in the text box)
import java.awt.Color;
import java.awt.Dimension;
import java.util.ArrayList;
import java.util.List;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.SwingWorker;
import javax.swing.filechooser.FileNameExtensionFilter;
public class MyPanel4 extends JPanel {
/**
*
*/
private static final long serialVersionUID = 1L;
private JTextArea jcomp;
private JButton btn;
public MyPanel4() {
//construct components
jcomp = new JTextArea(1, 1);
jcomp.setBorder(BorderFactory.createDashedBorder(Color.BLACK));
btn = new JButton("open");
btn.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
final JFileChooser chooseFile = new JFileChooser();
FileNameExtensionFilter filter = new FileNameExtensionFilter(".txt", "txt");
chooseFile.setFileFilter(filter);
chooseFile.setAcceptAllFileFilterUsed(false);
chooseFile.setMultiSelectionEnabled(true);
int returnVal = chooseFile.showOpenDialog(MyPanel4.this);
if (returnVal == JFileChooser.APPROVE_OPTION) {
final File[] files = chooseFile.getSelectedFiles();
new SwingWorker<Void, String>() {
private String testfile1 = files[0].getPath();
private String testfile2 = files[1].getPath();
private String testfile3 = files[2].getPath();
protected Void doInBackground() {
List<String> b = new ArrayList<String>();
b.add(testfile1);
b.add(testfile2);
b.add(testfile3);
publish(b.get(0));
publish(b.get(1));
publish(b.get(2));
return null;
}
#Override
protected void process(List<String> chunks) {
for (String pathname : chunks)
{
jcomp.append(pathname + "\n");
}
}
protected void done() {
try
{
System.out.println("Opration Completed");
} catch (Exception e) {
e.printStackTrace();
}
}
}.execute();
}
}
});
//adjust size and set layout
setPreferredSize(new Dimension(944, 575));
BoxLayout layout = new BoxLayout(this, BoxLayout.Y_AXIS);
setLayout(layout);
//add main components
add(jcomp);
add(btn);
}
public static void main(String[] args) {
JFrame frame = new JFrame("MyTest");
frame.getContentPane();
frame.add(new MyPanel4());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setVisible(true);
}
}

The SwingWorker should be created inside the buttons actionPerformed method, so that when you click the button, it will run the SwingWorker
You should, also, make sure that all interactions with user interface are fine from within the context of the Event Dispatching Thread. This means you should ask the user to select the file fro within the context of the actionPerformed method and pass the result to the SwingWorked
Updated
Two additional things...
You're not actually reading the file, but simply passing the name of the file to the publish method
SwingWorker defines process as protected void process(List<V> chunks) but you've defined it as protected void process(String s)...mean that you are actually not overriding the SwingWorker's process method, but creating your own...
Take a look at this example to see how you might be able to use a SwingWorker to read a file...
And, update your process to have the corrected method signature...
#Override
protected void process(List<String> chunks) {
for (String line : chunks) {
output.append(line);
}
}
Remember, you should, as much as possible, use the #Override annotation when you think you are overriding a method, the compiler will tell you when you are mistaken, saving you a lot of head scratching...

It should be like this:
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.SwingWorker;
import javax.swing.filechooser.FileNameExtensionFilter;
public class MyPanel3 extends JPanel {
/**
*
*/
private static final long serialVersionUID = 1L;
private JTextArea jcomp;
private JButton btn;
private String testfile;
public MyPanel3() {
//construct components
jcomp = new JTextArea(1, 1);
jcomp.setBorder(BorderFactory.createDashedBorder(Color.BLACK));
btn = new JButton("open");
btn.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
final JFileChooser chooseFile = new JFileChooser();
FileNameExtensionFilter filter = new FileNameExtensionFilter(".txt", "txt");
chooseFile.setFileFilter(filter);
chooseFile.setAcceptAllFileFilterUsed(false);
chooseFile.setMultiSelectionEnabled(true);
int returnVal = chooseFile.showOpenDialog(MyPanel3.this);
if (returnVal == JFileChooser.APPROVE_OPTION) {
File[] files = chooseFile.getSelectedFiles();
testfile = files[0].getPath();
new SwingWorker<Void, String>() {
protected Void doInBackground() {
publish(testfile);
return null;
}
protected void process(String s) {
jcomp.append(s);
}
protected void done() {
try {
//System.out.println("The operation was completed");
} catch (Exception e) {
e.printStackTrace();
}
}
}.execute();
}
}
});
//adjust size and set layout
setPreferredSize(new Dimension(944, 575));
BoxLayout layout = new BoxLayout(this, BoxLayout.Y_AXIS);
setLayout(layout);
//add main components
add(jcomp);
add(btn);
}
public static void main(String[] args) {
JFrame frame = new JFrame("MyTest");
frame.getContentPane();
frame.add(new MyPanel3());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setVisible(true);
}
}
You are running worker when you are creating panel. But you should run it when button is clicked.

jFileChooser to save file of selected tab

Ok so I have a text editor made that can so far create new files and open files using jFileChooser.
What I am trying to do is get the saving of files to work.
Everytime you add or open a few file it adds a new tab to the tabbedpane and the name will be either file 1 etc or the name of the file opened.
When you click the save button the save dialog opens up
int returnVal = fileChooser.showSaveDialog(this);
I want the name on the tab to be inserted to the name of file field.
Also how do I make a file of the current selected tabs textarea? I have tried this but its a no go:
int index = tabbedPane.getSelectedIndex();
Component c = tabbedPane.getComponentAt(index);
JTextArea a = (JTextArea) c;
System.out.println(a.getText());
File file = new File(a.getText());
fileChooser.setSelectedFile(file);
So I need to make a file of the string in the textArea I guess.

Following up #Andrew's answer, here is a snippet illustrating what he meant. I took the liberty to rather use a OutputStreamWriter than a FileWriter because this allows you to choose the charset used to write the file, which is something that you usually want to control and not rely on the "random" default platform charset.
import java.awt.BorderLayout;
import java.awt.Desktop;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.UnsupportedEncodingException;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;
public class TestTextArea {
private JTextArea textArea;
private JButton save;
protected void initUI() {
JFrame frame = new JFrame(TestTextArea.class.getSimpleName());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
textArea = new JTextArea(24, 80);
save = new JButton("Save to file");
save.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
saveToFile();
}
});
frame.add(new JScrollPane(textArea));
JPanel buttonPanel = new JPanel();
buttonPanel.add(save);
frame.add(buttonPanel, BorderLayout.SOUTH);
frame.setSize(500, 400);
frame.setVisible(true);
}
protected void saveToFile() {
JFileChooser fileChooser = new JFileChooser();
int retval = fileChooser.showSaveDialog(save);
if (retval == JFileChooser.APPROVE_OPTION) {
File file = fileChooser.getSelectedFile();
if (file != null) {
if (!file.getName().toLowerCase().endsWith(".txt")) {
file = new File(file.getParentFile(), file.getName() + ".txt");
}
try {
textArea.write(new OutputStreamWriter(new FileOutputStream(file), "utf-8"));
Desktop.getDesktop().open(file);
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new TestTextArea().initUI();
}
});
}
}

An easy way is to use JTextComponent.write(Writer). JTextArea extends JTextComponent.
For the Writer use a FileWriter.

You need to, some how associate the File that was opened with the tab. That way, you can look up the File associated based on the selected tab.
Something like HashMap<Component, File> for example