Develop Reference

How set JLabel at center of JDialog on X? [duplicate]

I'm using the NetBeans GUI builder to handle my layout (I'm terrible with LayoutManagers) and am trying to place a simple JLabel so that it is always centered (horizontally) inside its parent JPanel. Ideally, this would maintain true even if the JPanel was resized, but if that's a crazy amount of coding than it is sufficient to just be centered when the JPanel is first created.
I'm bad enough trying to handle layouts myself, but since the NetBeans GUI Builder autogenerates immutable code, it's been impossible for me to figure out how to do this centering, and I haven't been able to find anything online to help me.
Thanks to anybody who can steer me in the right direction!

Here are four ways to center a component:
import java.awt.*;
import javax.swing.*;
import javax.swing.border.*;
class CenterComponent {
public static JLabel getLabel(String text) {
return getLabel(text, SwingConstants.LEFT);
}
public static JLabel getLabel(String text, int alignment) {
JLabel l = new JLabel(text, alignment);
l.setBorder(new LineBorder(Color.RED, 2));
return l;
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
JPanel p = new JPanel(new GridLayout(2,2,4,4));
p.setBackground(Color.black);
p.setBorder(new EmptyBorder(4,4,4,4));
JPanel border = new JPanel(new BorderLayout());
border.add(getLabel(
"Border", SwingConstants.CENTER), BorderLayout.CENTER);
p.add(border);
JPanel gridbag = new JPanel(new GridBagLayout());
gridbag.add(getLabel("GridBag"));
p.add(gridbag);
JPanel grid = new JPanel(new GridLayout());
grid.add(getLabel("Grid", SwingConstants.CENTER));
p.add(grid);
// from #0verbose
JPanel box = new JPanel();
box.setLayout(new BoxLayout(box, BoxLayout.X_AXIS ));
box.add(Box.createHorizontalGlue());
box.add(getLabel("Box"));
box.add(Box.createHorizontalGlue());
p.add(box);
JFrame f = new JFrame("Streeeetch me..");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setContentPane(p);
f.pack();
f.setLocationByPlatform(true);
f.setVisible(true);
}
});
}
}

By using Borderlayout, you can put any of JComponents to the CENTER area. For an example, see an answer to Stack Overflow question Get rid of the gap between JPanels. This should work.

Even with BoxLayout you can achieve that:
JPanel listPane = new JPanel();
listPane.setLayout(new BoxLayout(listPane, BoxLayout.X_AXIS ));
JLabel label = new JLabel();
listPane.add(Box.createHorizontalGlue());
listPane.add(label);
listPane.add(Box.createHorizontalGlue());
mKorbel's solution is perfect for your goal. Anyway I always like to suggest BoxLayout because it's very flexible.

Mara: "thanks for your response, however the NetBeans GUI Build uses GroupLayout and this is not overridable."
Not true! Right click anywhere inside JFrame (or any other GUI container) in NetBeans GUI builder and select "Set Layout". By default is selected "Free Design", which is Group layout, but you can select any other layout including Border layout as advised by mKorbel.

There's many ways to do this, depending on the layout manager(s) you use. I suggest you read the Laying Out Components Within a Container tutorial.
I believe the following will work, regardless of layout manager:
JLabel.setHorizontalAlignment(SwingConstants.CENTER)

JFrame turns blue when adding tabs

I currently have a Jframe that I want to add to a tab instead.
(I used a frame just for testing purposes, to make sure the look and feel is correct, but when trying to add it to a JTabbedPane, the frame starts to look blue (weird top aswell).
I tried copying my settings from my original frame to the new frame but that did not help.
JTabbedPane tabs = new JTabbedPane();
tabs.addTab("1", frame.getContentPane());
JFrame FinalFrame = new JFrame();
FinalFrame.setDefaultLookAndFeelDecorated(true);
FinalFrame.setSize(WIDTH, HEIGTH);
FinalFrame.setLocation(100, 150);
FinalFrame.setTitle("Primal-Pvm Notification center");
FinalFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
FinalFrame.add(tabs);
Side by side view of the problem and the frame before adding it to the tab:
Edit: Answer by George Z. helped me out a lot.
Like he said to solve the problem:
Don't add things to your main frame but add them to a Jpanel and add that to a JTabbedPane.
If you have a Jpanel that you are adding to a tab that contains an override in the paintComponent, you have to create that class as the Jpanel so:
JPanel panel = new LineDrawer([Enter parameters]);
panel.setLayout([Enter Layout]);

The way you are approaching this seems to be pretty complex hence this weird behavior. (Looks like a look and feel problem? - show the part of the code that sets it)
However, I suggest you to create only one JFrame (this question explains why you should do that), set the layout of its content pane to BorderLayout and keep it like this. Its a rare situation to mess up with content panes. After that create independent JPanels representing the tab(s) you would like to have. Finally create a JTabbedPane with these panels and add it to the content frame of the JFrame.
A small example would be:
public class TabbedPanelExample extends JFrame {
public TabbedPanelExample() {
super("test");
setDefaultCloseOperation(EXIT_ON_CLOSE);
setLayout(new BorderLayout());
JTabbedPane pane = new JTabbedPane();
pane.addTab("FirstTab", createFirstTab());
pane.addTab("SecondTab", createSecondTab());
add(pane);
setSize(400, 400);
setLocationRelativeTo(null);
}
private Component createFirstTab() {
JPanel panel = new JPanel(new FlowLayout());
panel.add(new JLabel("Some Component"));
panel.add(new JTextField("Some Other Component"));
return panel;
}
private Component createSecondTab() {
JPanel panel = new JPanel(new FlowLayout());
panel.add(new JLabel("Some Component"));
panel.add(new JButton("Some Other Component"));
return panel;
}
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> {
new TabbedPanelExample().setVisible(true);
});
}
}
Post edit based on this comment:
Well I do have a Jframe with a lot of elements added to it so it kinda
is a hassle to switch it all to panels;
A JFrame cannot have a lot of elements. You take a look on how to use root panes. The container that "has a lot of elements" of a JFrame is its rootpane which is mostly completed by its contentpane. When you frame.add(component), you add the component to its content pane. Guess what? A JFrame's content pane is a JPanel. So are a already to panels.
Now in order to make this work, try to do as i said and frame.setLayout(new BorderLayout(); //changes layout to contentpane. Assuming you have a bunch of components (lets say comp1,comp2) and you are adding them like:
frame.add(comp1);
frame.add(comp2);
You must do the following in order to make it clear. Create a JPanel and instead of frame.add(comp1), do panel.add(comp1). So this JPanel has all the components you added in JFrame. After that create your JTabbedPane:
JTabbedPane pane = new JTabbedPane();
pane.addTab("tab", panel);
and finally add this pane to the content pane of your JFrame:
frame.add(pane);
In conclusion, you will move all the components you have added to your frame into a JPanel, add this JPanel to a JTabbedPane, and finally add this JTabbedPane to the frame (contentpane). Frame has only one component.

Centering a fixed size canvas in a JFrame

I'm in the process of creating a circuit editor (similar to any regular paint software with a basic menu and a canvas with specifiable dimensions). I am currently trying to transform the previously unscrollable canvas (JPanel) to a scrollable one.
The obvious design error at the moment is that while the scrollbars seem to correctly reflect the internal size of the canvas (which can of course be way bigger than the JFrame), due to the canvas JPanel being added in the CENTER of the BorderLayout of the master panel, it always resizes along with the JFrame.
public final class MainFrame extends JFrame
{
public MainFrame()
{
JPanel menuPanel = new JPanel(new FlowLayout(FlowLayout.LEFT));
// Populate Menu Panel
// ...
JPanel canvasPanel = new JPanel();
canvasPanel.setBackground(Color.white);
Dimension canvasDims = new Dimension(800,600);
canvasPanel.setPreferredSize(canvasDims);
canvasPanel.setMinimumSize(canvasDims);
canvasPanel.setMaximumSize(canvasDims);
JScrollPane canvasScrollPane = new JScrollPane(
canvasPanel,
JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
JPanel masterPanel = new JPanel(new BorderLayout());
masterPanel.add(menuPanel, BorderLayout.NORTH);
masterPanel.add(canvasScrollPane, BorderLayout.CENTER);
setContentPane(masterPanel);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(1200, 700);
setMinimumSize(new Dimension(500, 500));
setLocationRelativeTo(null);
setVisible(true);
}
I've read quite a few posts regarding centering JPanels and scrollbars but with both complexities added together, things might be a bit more complicated as I haven't yet found a solution.
What I'm really trying to achieve is to have the canvas' JPanel fixed in whatever size the user might have specified and centered in the middle as well as the scrollbars behaving as one would expect like in the beloved windows' paint:
How would you go about doing this/fixing my design? Any help would be greatly appreciated!
P.S. Happy new Year :)

JPanel fixed in whatever size the user might have specified and centered in the middle as well as the scrollbars behaving as one would expect
So you need to nest panels so the canvas panel can be displayed at its preferred size, while the parent panel resizes with the size of the frame.
An easy way to do this is with a JPanel that uses a GridBagLayout. Then you add the canvas panel to this panel using the default GridBagConstraints.
So the basic structure of the panels would be:
JPanel canvas = new JPanel();
canvas.setPreferredSize( new Dimension(300, 300) );
canvas.setBackground(Color.RED);
JPanel wrapper = new JPanel( new GridBagLayout() );
wrapper.add(canvas, new GridBagConstraints() );
frame.add(new JScrollPane(wrapper));
Note: there is no need for your "masterPanel". The default layout manager for the content pane of a JFrame is a BorderLayout, so you just add the "menuPanel" and "scrollPane" directly to the frame with the proper BorderLayout constraints.

JPanel within JPanel

Is it possible to have a panel within a panel in one method in Java?
Like If I created a JPanel within a method called, CreatePanel, could I add another one below it? I'm trying to add two or possibly three panels within one method but have not succeeded thus far.
If this is not possible, how would you create a JPanel, say LeftPanel, and add another JPanel within LeftPanel?
Any help with sources and clear explanation would be terrific because I'm a beginner at Java and sometimes when something you say might be obvious to you and all the CS-jocks but not to me.

What you ask is possible but i think you will learn more by reading the tutorial on layout managers than being given the answer. Please read up on layout managers and laying out components :)
http://docs.oracle.com/javase/tutorial/uiswing/layout/index.html

The basic premise would follow the same work flow for adding any other component to a panel...
You could do something like...
public JPanel createMasterPane() {
JPanel master = new JPanel(new BorderLayout());
JPanel leftPane = new JPanel();
leftPane.add(new JLabel("Left"));
master.add(leftPane, BorderLayout.WEST);
JPanel rightPanel = new JPanel();
rightPanel.add(new JLabel("Right"));
master.add(rightPanel, BorderLayout.EAST);
return master;
}
A better solution (IMHO) would be to separate the individual areas of responsibility and do something more like this...
public JPanel createLeftPane() {
JPanel leftPane = new JPanel();
leftPane.add(new JLabel("Left"));
return leftPane;
}
public JPanel createRightPane() {
JPanel rightPanel = new JPanel();
rightPanel.add(new JLabel("Right"));
return rightPanel;
}
public JPanel createMasterPane() {
JPanel master = new JPanel(new BorderLayout());
master.add(createLeftPane(), BorderLayout.WEST);
master.add(createRightPane(), BorderLayout.EAST);
return master;
}
You might like to spend some time looking through How to create a UI with Swing for more details...

Java Swing - JTable not showing

I'm having some troubles with Java Swing.
I'm trying to make a frame with a control panel at the top with some buttons in it.
and below that i want a JTable to show
I've been trying but the table is not showing.
If I remove the controlPanel at the top, it sometimes shows and sometimes not.
The code that I use inside my constructor of my JTable is provided in the same application,
so it's no network error
public ServerMainFrame(GuiController gc){
this.gc = gc;
initGUI();
}
private void initGUI() {
System.out.println("initiating GUI");
createFrame();
addContentPanel();
addControls();
//openPopUpServerSettings();
addSongTable();
}
private void createFrame()
{
this.setTitle("AudioBuddy 0.1");
this.setVisible(true);
this.setDefaultCloseOperation(EXIT_ON_CLOSE);
this.setSize(800, 600);
this.setResizable(false);
this.setLocationRelativeTo(null);
}
private void addContentPanel()
{
JPanel p = new JPanel();
p.setLayout(new FlowLayout());
p.setSize(new Dimension(800, 600));
this.setContentPane(p);
}
private void addControls()
{
JPanel controlPanel = new JPanel();
controlPanel.setLayout(new FlowLayout());
controlPanel.setBorder(BorderFactory.createLineBorder(Color.black));
controlPanel.setSize(700,100);
// Buttons
JButton play = new JButton("Play");
JButton pause = new JButton("Pause");
JButton stop = new JButton ("Stop");
JButton next = new JButton("Next");
JButton prev = new JButton("Previous");
controlPanel.add(play);
controlPanel.add(pause);
controlPanel.add(stop);
controlPanel.add(next);
controlPanel.add(prev);
// Currently playing
JLabel playing = new JLabel("Currently playing:");
controlPanel.add(playing);
JLabel current = new JLabel("Johnny Cash - Mean as Hell");
controlPanel.add(current);
this.getContentPane().add(controlPanel);
}
private void addSongTable()
{
JTable songTable = new JTable(Server.getSongTableModel());
songTable.setVisible(true);
JPanel tablePanel = new JPanel();
tablePanel.setVisible(true);
tablePanel.add(songTable);
songTable.repaint();
this.getContentPane().add(tablePanel);
JButton btnMulticastList = new JButton("send list to clients");
btnMulticastList.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent arg0) {
Server.MulticastPlaylist();
}
});
getContentPane().add(btnMulticastList);
}

if I remove the controlPanel at the top, it sometimes shows and
sometimes not.
everything is hidden in Server.getSongTableModel(), nobody knows without posting an SSCCE with hardcoded value returns from
GUI has issue with Concurency in Swing
XxxModel loading data continiously with building GUi, then exception caused described problems
The code that I use inside my constructor of my JTable is provided in
the same application, so it's no network error
no idea what you talking about
have to create an empty GUI, see InitialTread
showing GUI, then to start loading data to JTable
then starting Workers Thread (Backgroung Task) from SwingWorker or (descr. Network issue) better Runnable#Thread (confortable for catching an exceptions and processing separate threads)
output from Runnable to the Swing GUI must be wrapped into invokeLater()

If you want controls at the top of your window, and the table filling the majority of the window, then I'd suggest you try using BorderLayout instead of FlowLayout. Create it like this...
private void addContentPanel()
{
JPanel p = new JPanel();
p.setLayout(new BorderLayout());
p.setSize(new Dimension(800, 600));
this.setContentPane(p);
}
And add the components by specifying the location in the BorderLayout. In this case, the controls should be added to the top in their minimal size...
this.getContentPane().add(controlPanel,BorderLayout.NORTH);
And the table should be in the center, filling the remaining window space...
this.getContentPane().add(tablePanel,BorderLayout.CENTER);
In your case, you also have a button at the bottom...
getContentPane().add(btnMulticastList,BorderLayout.SOUTH);
For the layout you're after, BorderLayout is much more appropriate. The benefit of using BorderLayout here is that the components should be automatically resized to the size of the window, and you're explicitly stating where each component resides, so panels shouldn't not appear.
It would also be my recommendation that you find an alternative to calling getContentPane() in all your methods. Maybe consider keeping a global variable for the main panel, like this...
private mainPanel;
private void addContentPanel()
{
mainPanel = new JPanel(new BorderLayout());
mainPanel.setSize(new Dimension(800, 600));
this.setContentPane(mainPanel);
}
Then you can reference the panel directly when you want to add() components to it.
Finally, I'd also suggest using GridLayout for your controls, as it will allow you to place all your buttons in it, and they'll be the same size for consistency. Define it like this to allow 5 buttons in a horizontal alignment...
JPanel controlPanel = new JPanel(new GridLayout(5,1));
then you just add the buttons normally using controlPanel.add(button) and they'll be added to the next slot in the grid.
For more information, read about GridLayout or BorderLayout, or just see the Java Tutorial for a Visual Guide to Layout Managers to see what alternatives you have and the best one for your situation. In general, I try to avoid FlowLayout, as I find that there are other LayoutManagers that are more suitable in the majority of instances.