Develop Reference

Get the in-focus tab after closing a tab

In a JTabbedPane, I associated a custom-made Data object to each added tab. I also have a corresponding Metadata object that shows up in another panel when the tab is selected. The problem I have now is when a tab is closed, the metadata panel shows the metadata of the Data object in the tab that just gets closed. Ideally, I want the panel to show the metadata for the in-focus tab that the user sees. However, the act of closing a tab means the “selected tab” is the tab being closed, so tabpane.getSelectedIndex() would not work. How can I get the tab that is in focus after closing a tab? Thank you in advance!

Devil is in the detail, which you provided none.
I did a quick test and discovered that, ChangeListener is called before ContainerListener, which is a real pain, but, it was always reporting the correct index.
So, what you need to do is marry the two together, so that, both will update the meta data pane when they are called.
import java.awt.EventQueue;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ContainerEvent;
import java.awt.event.ContainerListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTabbedPane;
public class Test {
public static void main(String[] args) {
new Test();
}
public Test() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
JTabbedPane tabbedPane = new JTabbedPane();
tabbedPane.addTab("One", new TabPane(tabbedPane));
tabbedPane.addTab("Two", new TabPane(tabbedPane));
tabbedPane.addTab("Three", new TabPane(tabbedPane));
tabbedPane.addTab("Four", new TabPane(tabbedPane));
tabbedPane.addContainerListener(new ContainerListener() {
#Override
public void componentAdded(ContainerEvent e) {
}
#Override
public void componentRemoved(ContainerEvent e) {
System.out.println("Removed " + e.getChild());
}
});
tabbedPane.addChangeListener(new ChangeListener() {
#Override
public void stateChanged(ChangeEvent e) {
System.out.println(tabbedPane.getSelectedIndex());
}
});
JFrame frame = new JFrame();
frame.add(tabbedPane);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TabPane extends JPanel {
private JTabbedPane parent;
public TabPane(JTabbedPane parent) {
this.parent = parent;
setLayout(new GridBagLayout());
JButton btn = new JButton("Close");
add(btn);
btn.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
parent.remove(TabPane.this);
}
});
}
}
}

jSplitPane Showing and Hiding Left Pane when Mouse over

I'm working on an application that allows me to show and hide split planes.
I've read some articles on how to get this but its not what I'm looking for.
here's the code Ive written:
Im currently using netbeans.
private void jSplitPane1MouseEntered(java.awt.event.MouseEvent evt) {
if(MouseInfo.getPointerInfo().getLocation() == jSplitPane1.getLeftComponent().getLocation()){
jSplitPane1.setDividerLocation(100);
System.out.println("Mouse Entered");
}else{
jSplitPane1.setDividerLocation(20);
System.out.println("Mouse Exited");
}
}
I have referred to these posts:
How to make JSplitPane auto expand on mouse hover?
Get Mouse Position
What I want to happen is when I mouse over the left side of the jSplitPane, I would get the divider to extend to 100 as per my first if statement, and when it exists the left side, it contracts back to divider location 20.

This is really, really tricky.
You could use a MouseListener on the "left" component and monitor the mouseEntered and mouseExited events, but these will also get triggered when when you move into and out of a child component which has a MouseListener of it's own (like a JButton).
Okay, you could use a MouseMotionListener on the JSplitPane and monitor for the mouseMoved event and check where the mouse cursor is, but this goes to hell the moment the components (left/right) get their own MouseListener, as the MouseEvents are no longer delivered to the JSplitPane
So, one of the last options you have is to attach a global AWTListener to the event queue and monitor for events which occur on the JSplitPane itself, for example...
import java.awt.AWTEvent;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.GridBagLayout;
import java.awt.Toolkit;
import java.awt.event.AWTEventListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSplitPane;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class Main {
public static void main(String[] args) {
new Main();
}
public Main() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
ex.printStackTrace();
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
public TestPane() {
setLayout(new BorderLayout());
JSplitPane pane = new JSplitPane();
pane.setLeftComponent(makePane(Color.RED));
pane.setRightComponent(makePane(Color.BLUE));
Toolkit.getDefaultToolkit().addAWTEventListener(new AWTEventListener() {
#Override
public void eventDispatched(AWTEvent event) {
if (event instanceof MouseEvent) {
MouseEvent me = (MouseEvent) event;
if (pane.getBounds().contains(me.getPoint())) {
System.out.println("Global Motion in the pane...");
me = SwingUtilities.convertMouseEvent(me.getComponent(), me, pane);
Component left = pane.getLeftComponent();
if (left.getBounds().contains(me.getPoint())) {
pane.setDividerLocation(100);
} else {
pane.setDividerLocation(20);
}
}
}
}
}, MouseEvent.MOUSE_MOTION_EVENT_MASK);
// You don't need this, this is to demonstrate
// that mouse events aren't hitting your component
// via the listener
pane.addMouseMotionListener(new MouseAdapter() {
#Override
public void mouseMoved(MouseEvent e) {
System.out.println("Motion in the pane...");
Component left = pane.getLeftComponent();
if (left.getBounds().contains(e.getPoint())) {
pane.setDividerLocation(100);
} else {
pane.setDividerLocation(20);
}
}
});
pane.setDividerLocation(20);
add(pane);
}
protected JPanel makePane(Color background) {
JPanel pane = new JPanel() {
#Override
public Dimension getPreferredSize() {
return new Dimension(100, 100);
}
};
pane.setLayout(new GridBagLayout());
pane.add(new JButton("..."));
pane.setBackground(background);
pane.addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
System.out.println("...");
}
});
return pane;
}
}
}

Select text in 2 JTextarea at the same time

I am trying to do a small app that compares two similar texts contained in 2 JTextarea. I am wondering if it's possible to select text from the first JTextarea and automatically select the text on the second JTeaxtarea (lets consider that it's guarantee that the 2 JTextarea will have the same text for now) ?
Should I share events or listeners ?
Thank you

This would be so much easier if JTextComponent supported a selection model...
Basically, what you can do is attach a ChangeListener to the JTextArea's Caret and monitor for changes to the Caret, changing the selection of the other JTextArea in response...
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.event.CaretEvent;
import javax.swing.event.CaretListener;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
import javax.swing.text.BadLocationException;
import javax.swing.text.DefaultHighlighter;
public class MirrorTextSelection {
public static void main(String[] args) {
new MirrorTextSelection();
}
public MirrorTextSelection() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
private JTextArea left;
private JTextArea right;
private DefaultHighlighter.DefaultHighlightPainter highlightPainter;
public TestPane() {
highlightPainter = new DefaultHighlighter.DefaultHighlightPainter(UIManager.getColor("TextArea.selectionBackground"));
left = new JTextArea(20, 20);
left.setWrapStyleWord(true);
left.setLineWrap(true);
right = new JTextArea(20, 20);
right.setWrapStyleWord(true);
right.setLineWrap(true);
left.setText("I am trying to do a small app that compares two similar texts contained in 2 JTextarea. I am wondering if it's possible to select text from the first JTextarea and automatically select the text on the second JTeaxtarea (lets consider that it's guarantee that the 2 JTextarea will have the same text for now) ? Should I share events or listeners ? Thank you");
right.setText("I am trying to do a small app that compares two similar texts contained in 2 JTextarea. I am wondering if it's possible to select text from the first JTextarea and automatically select the text on the second JTeaxtarea (lets consider that it's guarantee that the 2 JTextarea will have the same text for now) ? Should I share events or listeners ? Thank you");
setLayout(new GridLayout(0, 2));
add(new JScrollPane(left));
add(new JScrollPane(right));
left.getCaret().addChangeListener(new ChangeListener() {
#Override
public void stateChanged(ChangeEvent e) {
int dot = left.getCaret().getDot();
int mark = left.getCaret().getMark();
right.setCaretPosition(mark);
right.moveCaretPosition(dot);
}
});
}
}
}
Now, when you run this, you will find that the right side doesn't seem to get highlighted...what?!
The selection is changing, it's just not been rendered because the component doesn't have focus...
Instead, you could use a Highlighter to highlight the text...
private DefaultHighlighter.DefaultHighlightPainter highlightPainter;
//...
highlightPainter = new DefaultHighlighter.DefaultHighlightPainter(UIManager.getColor("TextArea.selectionBackground"));
left.getCaret().addChangeListener(new ChangeListener() {
#Override
public void stateChanged(ChangeEvent e) {
int dot = left.getCaret().getDot();
int mark = left.getCaret().getMark();
right.getHighlighter().removeAllHighlights();
try {
int start = Math.min(dot, mark);
int end = Math.max(dot, mark);
right.getHighlighter().addHighlight(start, end, highlightPainter);
} catch (BadLocationException ex) {
ex.printStackTrace();
}
}
});
Okay, this is now working and you can control the background color of the highlight...
There is another alternative...We can replace the Caret of the right JTextArea with one that doesn't hide the selection when focus is lost...
public class HighlightCaret extends DefaultCaret {
#Override
public void install(JTextComponent c) {
super.install(c);
setSelectionVisible(true);
}
#Override
public void focusGained(FocusEvent e) {
JTextComponent component = getComponent();
if (component.isEnabled()) {
if (component.isEditable()) {
setVisible(true);
}
setSelectionVisible(true);
}
}
#Override
public void focusLost(FocusEvent e) {
setVisible(false);
}
}
Then we set the Caret to right...
right.setCaret(nwe HighlightCaret());
This means we don't need the Highlighter code, we can stick with the original and we get control over not only the background selection color but also the foreground selection color as well...

Why does viewport changelistener get called multiple times

I've got a viewport, and I've attached a change listener to it. Whenever I scroll through my viewport, my change listener gets called about four times. I'm not sure how to avoid this; I only want the call to happen once?

There's no way around this, JViewport will fire several stateChanged events because it's providing notification about changes to a number of properties...
From the JavaDocs...
Adds a ChangeListener to the list that is notified each
time the view's size, position, or the viewport's extent size has
changed.
At this point, it's kind of hard to know what to suggest as we don't know what it is you are trying to achieve, however, if you have to use a ChangeListener, you could set up a coalescing mechanism. That is, rather then responding to each event, you basically wait until a long enough delay has occurred between events before responding to it...
For example...
public class DelayedChangeHandler implements ChangeListener {
private Timer timer;
private ChangeEvent last;
public DelayedChangeHandler() {
timer = new Timer(250, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
stableStateChanged();
}
});
timer.setRepeats(false);
}
#Override
public void stateChanged(ChangeEvent e) {
last = e;
timer.restart();
}
protected void stableStateChanged() {
System.out.println("Finally...");
}
}
Basically, this is a ChangeListener implementation that uses a non-repeating javax.swing.Timer with a short delay. Each time stateChanged is called, the timer is restart. Finally, when the timer is allowed to "tick", it calls stableStateChanged indicating that enough time has passed since the last event was raised.
This assumes that you don't so much care about what caused the event, only that the event occured...
A runnable example...
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
public class TestViewport {
public static void main(String[] args) {
new TestViewport();
}
public TestViewport() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
}
JPanel pane = new JPanel() {
#Override
public Dimension getPreferredSize() {
return new Dimension(1000, 1000);
}
};
JScrollPane sp = new JScrollPane(pane);
sp.getViewport().addChangeListener(new DelayedChangeHandler());
sp.getViewport().addPropertyChangeListener(new PropertyChangeListener() {
#Override
public void propertyChange(PropertyChangeEvent evt) {
System.out.println(evt.getPropertyName());
}
});
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(sp);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class DelayedChangeHandler implements ChangeListener {
private Timer timer;
private ChangeEvent last;
public DelayedChangeHandler() {
timer = new Timer(250, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
stableStateChanged();
}
});
timer.setRepeats(false);
}
#Override
public void stateChanged(ChangeEvent e) {
last = e;
timer.restart();
}
protected void stableStateChanged() {
System.out.println("Finally...");
}
}
}

You can try to use AdjustmentListener for gettign scroll event once, try next:
import java.awt.event.AdjustmentEvent;
import java.awt.event.AdjustmentListener;
import java.io.UnsupportedEncodingException;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
public class Example {
public static void main(String[] args) throws UnsupportedEncodingException {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
final JScrollPane pane = new JScrollPane(new JTextArea());
pane.getVerticalScrollBar().addAdjustmentListener(new AdjustmentListener() {
#Override
public void adjustmentValueChanged(AdjustmentEvent e) {
if(e.getValueIsAdjusting()){
return;
}
System.out.println("vertical scrolled");
System.out.println("bar value = " + e.getValue());
}
});
frame.setContentPane(pane);
frame.setSize(300, 200);
frame.setVisible(true);
}
}
Here is another example.

Implementing a simple hover effect on a Jlabel

I am messing around with some ideas for a side project and I would like to create a GUI using Java swing that doesn't look like it is from Windows95. One of the ideas I was kicking around was to use JLabels as buttons instead of the standard JButton. This would allow me to customize hover, drag, and movement effects as I like.
Research into the MouseAdapter class should allow me to do everything I intend, unfortunately I am having some trouble implementing the hover effect as I wanted as the JLabel does not appear to update. I have tried updating the Frame directly by calling frame.update(getGraphics()); but that does not appear to work as I think it does.
Can I get some advice on how to update the label properly.
Note: This is just an example with no effort put in to organize the code efficiently
public class Window extends JFrame {
/**
*
*/
private static final long serialVersionUID = 5259700796854880162L;
private JTextField textField;
private JLabel lblNewLabel;
static Window frame;
int i = 0;
public Window() {
JPanel panel = new JPanel();
getContentPane().add(panel, BorderLayout.CENTER);
panel.setLayout(null);
lblNewLabel = new JLabel("New label");
lblNewLabel.setBackground(Color.LIGHT_GRAY);
lblNewLabel.setBounds(137, 38, 114, 70);
panel.add(lblNewLabel);
lblNewLabel.addMouseListener(new LabelAdapter());
textField = new JTextField();
textField.setBounds(122, 119, 86, 20);
panel.add(textField);
textField.setColumns(10);
}
private class LabelAdapter extends MouseAdapter {
#Override
public void mouseClicked(MouseEvent e) {
textField.setText(String.valueOf(i));
i++;
}
#Override
public void mouseEntered(MouseEvent e) {
lblNewLabel.setBackground(Color.CYAN);
}
#Override
public void mouseExited(MouseEvent e) {
lblNewLabel.setBackground(Color.LIGHT_GRAY);
}
}
/**
* #param args
*/
public static void main(String[] args) {
frame = new Window();
frame.setSize(900, 700);
frame.setVisible(true);
}
}

Window is reserver name for awt.Window, change this name to e.g. MyWindow
JPanel has implemented FlowLayout, you can't to use NullLayout use built_in LayoutManager, then to use JFrame.pack() before JFrame.setVisible for proper sizing on the screen
JLabel is transparent, change that by using JLabel.setOpaque(true);
refresh of Backgroung Color from Mouse over/hover isn't possible without JLabel.repaint() as last code line in concrete mouse_event, repaint() missing in JLabel API

On top of mKorbel's answer...
I don't know why you're going to so much effort, when you could actually make a button look like a label.
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.ButtonModel;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
public class NotALabel {
public static void main(String[] args) {
new NotALabel();
}
public NotALabel() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
ex.printStackTrace();
}
final JButton btn = new JButton("Am I label or a button?");
btn.setContentAreaFilled(false);
btn.setBorderPainted(false);
btn.setFocusPainted(false);
btn.setOpaque(true);
btn.getModel().addChangeListener(new ChangeListener() {
#Override
public void stateChanged(ChangeEvent e) {
ButtonModel model = (ButtonModel) e.getSource();
if (model.isRollover()) {
btn.setBackground(Color.CYAN);
} else {
btn.setBackground(null);
}
}
});
btn.addActionListener(new ActionListener() {
private int count = 0;
#Override
public void actionPerformed(ActionEvent e) {
count++;
((JButton) e.getSource()).setText("I'm a super button!! Or label...");
}
});
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new GridBagLayout());
frame.add(btn);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
}
You should also consider trying to Setting the look and feel or even possibly Modifying the look and feel