Centering a JLabel in a JPanel

Centering a JLabel in a JPanel - java

I have a panel derived from JPanel. I have a custom control derived from JLabel. I am attempting to center this custom JLabel on my panel.
The only way I know to do this that will work is to use the a null layout (setLayout(null)) and then calculate the custom JLabel's setLocation() point so that it's in the right spot.
The custom JLabel is physically moved from one panel to this panel in this app and I believe the location previously set in setLocation is affecting things. However when I set it to (0,0) the component goes up into the upper left corner.
BorderLayout doesn't work because when only 1 component is provided and placed into BorderLayout.CENTER, the central section expands to fill all of the space.
An example I cut and pasted from another site used BoxLayout and component.setAlignmentX(Component.CENTER_ALIGNMENT). This didn't work either.
Another answer mentioned overriding the panel's getInset() function (I think that's what it was called), but that proved to be a dead end.
So far I'm working with a panel with a GridBagLayout layout and I include a GridBagConstraints object when I insert the custom JLabel into my panel. This is inefficient, though. Is there a better way to center the JLabel in my JPanel?

Set GridBagLayout for JPanel, put JLabel without any GridBagConstraints to the JPanel, JLabel will be centered
example
import java.awt.*;
import javax.swing.*;
public class CenteredJLabel {
private JFrame frame = new JFrame("Test");
private JPanel panel = new JPanel();
private JLabel label = new JLabel("CenteredJLabel");
public CenteredJLabel() {
panel.setLayout(new GridBagLayout());
panel.add(label);
panel.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
frame.add(panel);
frame.setSize(400, 300);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
CenteredJLabel centeredJLabel = new CenteredJLabel();
}
});
}
}

Supose your JLabel is called label, then use:
label.setHorizontalAlignment(JLabel.CENTER);

Forget all the LayoutManagers in the Java Standard Library and use MigLayout. In my experience it's much easier to work with an usually does exactly what you expect it to do.
Here's how to accomplish what you're after using MigLayout.
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import net.miginfocom.swing.MigLayout;
public class Test
{
public static void main( String[] args )
{
JFrame frame = new JFrame( );
JPanel panel = new JPanel( );
// use MigLayout
panel.setLayout( new MigLayout( ) );
// add the panel to the frame
frame.add( panel );
// create the label
JLabel label = new JLabel( "Text" );
// give the label MigLayout constraints
panel.add( label, "push, align center" );
// show the frame
frame.setSize( 400, 400 );
frame.setVisible( true );
}
}
Most of that is just boilerplate. The key is the layout constraint: "push, align center":
align center tells MigLayout to place the JLabel in the center of its grid cell.
push tells MigLayout to expand the grid cell to fill available space.

BoxLayout is the way to go. If you set up a X_AXIS BoxLayout, try adding horizontal glues before and after the component:
panel.add(Box.createHorizontalGlue());
panel.add(label);
panel.add(Box.createHorizontalGlue());

I don't like the answers here.
I've never seen a valid use of a GridBagLayout ever in my career. Not saying there isn't one, just saying I haven't seen [a valid] one, and there might be correlation there. Moreover, adding a single JLabel to the middle of a Container might make it center for demonstrational purposes, but you're going to have a lot harder of a time later on if you try to continue to work with that over some other layouts.
I do like the suggestion about the BoxLayout, because that is actually a great way to do it. That said, that answer is only part of the puzzle, hence why I'm dredging up a 7 year old question.
My 'Answer'
Really there is no short answer to your question. There is an exact answer to your question based on what you asked, but StackOverflow is about a community learning from each other, and I suspect you're trying to learn how to use layouts in general (or you were 7 years ago) and telling you to type a combination of keys to do exactly your demo case is not going to teach you the answer.
I'm going to try not to explain any layouts that you can't web-search the answer for on your own (with a link to the Oracle tutorial at the end, because I think it explains the different layouts fairly well).
BoxLayout
BoxLayout is one way to do it, and there is already a code snippet to demo it above so I won't provide one. I'll expand on it to say that, just as mentioned, that only answers your question exactly, but doesn't really teach you anything. Glue, as the BoxLayout refers to it, basically gives you an equal amount of remaining real-estate between all the 'glue' currently in the Container. So, if you were to do something like
panel.add(Box.createHorizontalGlue());
panel.add(label);
panel.add(Box.createHorizontalGlue());
panel.add(otherLabel);
You would find that your JLabel is no longer centered, because the 'glue' is only the remaining real-estate left, after two JLabels were added to the Container which will be equally divided between the two 'slots' (two calls to Container#add(Component) with a glue parameter) in theContainer`.
BorderLayout
BorderLayout is another way to go about this. BorderLayout is broken down into 5 regions. BorderLayout#CENTER, as you might guess, is the center region. The important note about this layout and how it centers things is how it obeys sizes of the Component that is in the center. That I won't detail though; the Oracle tutorial at the end covers it well enough if you're interested, I think.
Worth Noting
I suppose you could use a GridLayout, but it's a more simple way to do it over a GridBagLayout, which I already said even that I think is not a good approach. So I won't detail this one either.
The Point of it All
Now all that said, I think all LayoutManagers are worth a look. Just like anything else with relation to programming - use the tool that fits the job. Don't just assume because you used X layout before, that you should always use X layout and no other layout is viable. Figure out what you want your display to look like, and how you think it should behave with respect to resizing components, and then pick what you think would work best.
Another dual meaning of picking the right tool, is that you don't have to just fit all of your components into one single Container and make one layout do everything. There is nothing stopping you (and I strongly encourage you to) use multiple Containers and group them all together. Control each Container with a layout that is appropriate for that section of the display, and a different layout for a different Container.
Important!!
The reason why this is very important is because each layout has rules and things that they obey, and other things that they respect, and then others that are effectively ignored (i.e. preferred, maximum, and minimum sizes, for instance). If you use different layouts [correctly], you will find your display accepts dynamically being resized while still obeying the shape that you wanted it to hold. This is a very important key difference between doing it the right way, and just settling with GridBagLayout.
JPanel outer = new JPanel(new BorderLayout());
JPanel centerPanel = new JPanel();
centerPanel.setLayout(new BoxLayout(centerPanel, BoxLayout.PAGE_AXIS));
JPanel southPanel = new JPanel(new CardLayout());
outer.add(centerPanel, BorderLayout.CENTER);
outer.add(southPanel, BorderLayout.SOUTH);
Figure out what is appropriate to your scenario, and go with that. There is no one-size-fits-all unless you want something overly cumbersome and made redundant by other layouts (i.e. GridBagLayout).
Oracle's Tutorial
If you've made it this far, then I think you're looking for as much information as you can get. In which case, I strongly encourage you to read Oracle's tutorial on layout managers because it lays out general details of them all very well: https://docs.oracle.com/javase/tutorial/uiswing/layout/visual.html

Use this.
labelName.setHorizontalAlignment(SwingConstants.CENTER);
or
labelName.setHorizontalAlignment(JPanel.CENTER);
Both of them must work.

Do like this instead of libraries and layouts :
JLabel jlabel = new JLabel("Label Text", SwingConstants.CENTER);
Make sure to import javax.swing.SwingConstants INTERFACE , BUT DO NOT IMPLEMENT IT. It contains only constants and no methods.
Put the JLabel in a JPanel or else it will come at the center of the JFrame or JWindow (your top level container).

Related

jLabel and jTable conflict [duplicate]

I am extremely new to Java Swing, and I'm having quite a bit of issues getting a nice layout going. I have checked out google, and even other answers on this website, but no information I find seems to solve the issue. Here is the result of my efforts:
As you can see, the label, text field, and button are all out of alignment. It is my goal for all of them to have the same left-hand border, and for the button and text field to have the same right-hand border, with these left and right hand borders being each the same distance from the left and righthand sides of my window.
Here are the important parts of my code:
public void run()
{
JFrame frame = new JFrame("Arduino Server");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
InstancePanel = new ServerGUIPanel();
frame.getContentPane().add(InstancePanel);
frame.pack();
frame.setVisible(true);
}
And, in ServerGUIPanel.java:
public ServerGUIPanel()
{
setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));
setPreferredSize(new Dimension(500, 500));
setBorder(new EmptyBorder(10, 10, 10, 10));
StatusLabel = new JLabel("STATUS: BOOTUP");
add(StatusLabel);
PortField = new JTextField();
PortField.setPreferredSize(new Dimension(5000, 20));
PortField.setMaximumSize(PortField.getPreferredSize());
PortField.setActionCommand("PortChanged");
add(PortField);
ConnectionButton = new JButton();
ConnectionButton.setPreferredSize(new Dimension(5000, 20));
ConnectionButton.setMaximumSize(ConnectionButton.getPreferredSize());
ConnectionButton.setActionCommand("ConnectionClicked");
add(ConnectionButton);
}
Does anyone have a simple solution to this? What am I doing wrong here?
Thank you very much!
--Georges Oates Larsen

Read the section from the Swing tutorial on How to Use BoxLayout for the basics of using a BoxLayout as well as a section on alignment issues.
Basically you need to make sure the alignmentX value of all components is set to be left aligned.
Also:
Don't use setPreferredSize() to set the size of a component. Each Swing component will determine its own preferred size.
Use Java naming conventions. Variable names should NOT start with an upper case character.

I would not recommend using setPreferredSize() AND setMaximumSize(). The latter will cause problems when stretching your main frame. [Your components will likely not want resize]
You should be using layout managers to handle all the alignments itself. I would stay away from using BoxLayout in this case, as different components want to size differently, and that will sway the alignment when added into your BoxLayout panel.
Moreover, you might want to give your main frame a layout as well.
Can you post how you used your GridBagLayout?

Java: Upgrading to a single window

So I have been coding Java for a few months now, and I have been using JOptionPane to display text and variables in my games. I want to upgrade to a single window like a normal game, but I want to only focus on simple buttons and text on the screen. I have tried learning JFrame and ActionListsner, but I failed to completley figure it out. JFrame really confused me.
My question is this: Is there an easier way beside JFrame to just have a window that I can have simple text, buttons and TextFields without the hassle of opening a bunch of windows with JOptionPane, making crap loads of ActionListeners with JFrame or having to get into GUI? If not, where can I find help on how to make games with JFrame?

You should be using a JFrame. Trust me, they aren't that hard to use. Using a JFrame, you could create multiple panels and switch between them using CardLayout.
Since you said you aren't sure about how JFrame works, I gave a short introduction to them at the end of this post. But first, lets first talk about how to solve your problem.
Switching Panels via CardLayout
When you want to switch whats being viewed in the window completely, you're gonna want an entirely different panel for that specific purpose (for example, one for Main Menu, and one for the game). CardLayout was created for this.
You specify a "deck" panel. This panel will hold all the other panels you wanna switch between (cards):
CardLayout layout = new CardLayout();
JPanel deck = new JPanel();
deck.setLayout(layout);
You'll need to maintain a reference to the layout (via a variable) so you can switch between panels.
Now that we have a "deck" panel, we need to add some cards. We do this by creating more JPanels, and specifying a name when we add it to the frame (constraints):
JPanel firstCard = new JPanel();
JPanel secondCard = new JPanel();
deck.add(firstCard, "first");
deck.add(secondCard, "second");
The first card added to the deck will always be the first one to show.
Once you have all your cards added, you can switch between them by calling layout.show(deck, "second");. This is how you use CardLayout to manage multiple panels within your container.
Creating listeners
There's no easier way to manage it. It only gets harder from there (bindings - I highly suggest you look into them). For listeners, there are 2 steps:
Create the listener
Add it to the component
Could be 1 if you created the listener "on the fly" using a lambda:
JButton button = new JButton();
//Java 8+
button.addActionListener(event -> {
//whenever you click the button, code in here triggers
});
For those who don't use Java 8, you will need to use an anonymous class:
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
//whenever you click the button, code in here triggers
}
});
Only some components support ActionListener. Anything that extends AbstractButton, like JMenuItem, JButton, JRadioButton, and more will support ActionListeners. JTextField also supports it, even though it's not an AbstractButton. Every component supports KeyListener, though, which can also be used to listen for input events from the user.
If you have any questions about this, let me know and I'll be glad to answer them.
Using Swing Components
JFrame
You initialize a JFrame:
JFrame frame = new JFrame();
You then want to set the defaultCloseOperation, to determine what happens when the window closes:
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
There are different options, but EXIT_ON_CLOSE will terminate your program after closing the window. If you do not set the defaultCloseOperation, then your window will close, but your program will still be running. BIG NO NO. If you don't want the entire program to exit when you close the frame, use DISPOSE_ON_CLOSE.
After you have the close operation, you might be tempted to set the size. This is bad practice. Your frame should size depending on what's inside of it. To do this, you add your components to your frame, then call pack():
JButton button = new JButton("Button");
frame.add(button);
//add other components
frame.pack();
This will ensure your frame sizes to fit what's inside of it. You should always design GUI from the inside out, to ensure you always have enough room for what you need.
Containers
JFrame is a Container. Containers are just components that hold other components. All containers should have a LayoutManager to manage how components are laid out and, if needed, sized. JFrame isn't the only container though. JPanel is actually a container that's meant to be added to another container (or window). You can add things to a JPanel, then add that panel to another container. This is how you keep things neatly organized. Containers are pretty straight forward, so there's not much to talk about.
Content Pane
When you create a JFrame, it comes along with something called the contentPane. It is a JPanel nested within the JFrame. When you do frame.add(button), you'll notice that add actually refers to the contentPane:
//in Container class
public Component add(Component comp) {
addImpl(comp, null, -1); //where it's added
return comp;
}
//In JFrame class (overriding)
protected void addImpl(Component comp, Object constraints, int index) {
if(isRootPaneCheckingEnabled()) {
getContentPane().add(comp, constraints, index); //adds to content pane instead
} else {
super.addImpl(comp, constraints, index); //if root panes were not supported, which they currently are
}
}
You too can grab the contentPane from the frame using
Container pane = frame.getContentPane();
The reason why the contentPane is in Container form is to ensure a strong API (if JPanels were no longer going to be used for this, we wouldn't need to worry about changing the method type of getContentPane). Although, since it IS a JPanel, you can cast it back to it's original form:
JPanel pane = (JPanel) frame.getContentPane();
Although it's usually not needed. Using it as a Container tends to work just fine.
Layouts
JFrame, by default, uses BorderLayout, but you can change this by calling the setLayout method of the container:
FlowLayout layout = new FlowLayout();
frame.setLayout(layout);
Before jumping into layouts, I want to mention that JPanels use FlowLayout as default, except for the frame's default contentPane, which you can also change by doing frame.setContentPane(...). The contentPane uses BorderLayout as default.
Now, lets talk about a couple, starting with the JFrame default: BorderLayout.
Some layouts require what are called constraints, which tell the layout how to handle that specific component that's being added. You specify these constraints when you add the component to the container:
frame.add(button, BorderLayout.SOUTH);
BorderLayout is pretty simple. You have 5 options: NORTH, SOUTH, EAST, WEST, or CENTER. (there are other values such as PAGE_START, which are interchangeable. It's best to just use the easier form)
All constraints for BorderLayout are static field variables that you call similar to how I did. BorderLayout is actually an easy layout to use, seeing how there's not much to it. Even though it's simplicity limits what you can do (you can only put it in a certain position like NORTH), you'd usually combine layouts to get the result you want. This layout can be very powerful when combined with other layouts.
FlowLayout is pretty straight forward, as well as other layouts out there. One of the less straight-forward ones would be GridBagLayout, which can be a really flexible layout. It can also be pretty complex, though, as the documentation even states.
When using GridBagLayout, you need to create a constraints object: GridBagConstraints. To work with GridBagLayout, you set the constraints using the constraints object, then add both the component and the constraints to the container:
frame.setLayout(new GridBagLayout());
GridBagConstraints gbc = new GridBagConstraints();
JButton button = new JButton("yoyoyo");
frame.add(button, gbc);
Even if we don't adjust the constraints, we MUST still specify it when adding a component to the container.
Lets say we had 4 buttons, and we wanted to put them side by side. You would adjust the constraint's gridx and gridy values:
JButton button = new JButton("1");
JButton button2 = new JButton("2");
JButton button3 = new JButton("3");
JButton button4 = new JButton("4");
frame.add(button, gbc);
gbc.gridx = 1; //or gridx += 1, or gridx = 1. gridx starts at 0
frame.add(button2, gbc);
gbc.gridx = 0; //must reset the value back to normal
gbc.gridy = 1;
frame.add(button3, gbc);
gbc.gridx = 1;
//since gridy already == 1, no need to change it
frame.add(button4, gbc);
We can use the same constraints object, as long as we reset values when needed.
GridBagLayout starts centered, and works from the center out, unless you specify otherwise. You cannot skip grid spaces either. Also, as you'll notice, all your buttons will be touching. If you wanted a little space between each component, you can set the insets of the constraints:
int top = 5, left = 5, bottom = 1, right = 1;
gbc.insets.set(top, left, bottom, right);
There is a LOT more to this layout, and sadly I just don't feel this is the best place to give the explanation to it all, seeing how it's already documented (I even added the link).
There are many other layouts out there. Get familiar with as many as you possibly can, then find the ones that'll help suit your needs. Positioning should ALWAYS rely on the LayoutManager that's being used. As for sizing, that kinda depends on the layout you're using.

I would highly recommend using JavaFX. It's a very nice fairly easy to use GUI system with nice looking and customizable controls. JavaFX events (basically ActionListeners) are pretty straightforward as well.
This should get you started: http://docs.oracle.com/javase/8/javafx/get-started-tutorial/get_start_apps.htm#JFXST804

I believe CardLayout is what you're looking for. With it, the programmer can choose which JPanels should be visible in the JFrame. Upon user interaction you can switch the contents of the JFrame without new JFrames or JOptionPanes popping up.
Is there an easier way than using Swing for simple games? Swing has a learning curve, but with the right resources and practice you can learn to build simple GUI applications pretty quickly.

How can I align these JPanels on the bottom of the surrounding JPanel?

I am learning to use swing so please bear with me. Have a look at the attached screenshot:
These are JLabels within a JLabel within a JFrame. I would like to move these inner JLabel (which are randomly generated in size and color at runtime) to the very bottom as though they were books on a shelf. I know about Layout managers, though I can't quite seem to find the proper one to do what I want. This screenshot shows the result of specifying none, thus it should default to FlowLayout.
The inner JLabels are just .add()ed without any placement done. SetLocation appears to do nothing whatsoever.
Can you help me out?

If I were you I'd add put those JLabels inside of a JPanel with a boxlayout then align that with a border layout. Here is some code to help you out:
JLabel outer = new JLabel();
outer.setLayout(new BorderLayout(0,0));
/** Add inner JLabels here. The other you add them is the order they will appear from to right**/
JPanel bookshelf = new JPanel();
bookshelf.setLayout(new BoxLayout(toolbar, BoxLayout.X_AXIS));
//Add your jlabels to the bookshelf
outer.add(bookshelf, BorderLayout.SOUTH);
Here is a great tutorial on layout managers.
Also here is a UI I designed which is similar to what I think you want.
Hope this helps you out.

avoid boxlayout overlapping

Here I go again... battling with swings!!! So I'm creating an online test which will be displayed in an applet. The number of questions in the tests isn't fixed, so I need to ask questions according to the test. In order to display the questions I created a question jpanel that then I added to container panel which be displayed in the applet. For the container panel I'm using a boxlayout that allows me to stack questions one on top of the other.
My issue is that after adding more than 5 questions to the container panel the questions start overlapping. So can anyone guide me?
First, how can I avoid the overlapping?
Second, does a jpanel have a fixed maximum size? Or is there a way I can make it big enough to fit all the test question in the panel container? I thought about embedding the panel in a jscrollpane or I don't know if once the container panel is embedded in the applet it will scroll down as I scroll down the browser... Thank you guys for any help
Here's a pic of what it looks like when there aren't many questions...
Here is the code...
public class Test extends JPanel {
public Test() {
setLayout(null);
JScrollPane scrollPane = new JScrollPane();
scrollPane.setBounds(0, 5, 712, 1200);
add(scrollPane);
JPanel panel = new JPanel();
scrollPane.setViewportView(panel);
panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
MultipleChoice q1 = new MultipleChoice();
panel.add(q1);
MultipleChoice q2 = new MultipleChoice();
panel.add(q2);
MultipleChoice q3 = new MultipleChoice();
panel.add(q3);
MultipleChoice q4 = new MultipleChoice();
panel.add(q4);
MultipleChoice q5 = new MultipleChoice();
panel.add(q5);
}
}

I'm guessing, and all I can do is guess without an sscce, but if your MultipleChoice JPanel uses null layout, then it won't be able to give a decent preferredSize to your layout managers allowing for overlapping components. If so, again the solution is to not use null layout, almost ever.
You state in comment:
I know buddy... But how can I be more specific when I don't know much about swings? I'm using Windowbuilder and that's the layout given when setting a container layout to absolute.
"buddy"?
regarding, "when I don't know much about swings": then learn about Swing. Go to the Layout Manager Tutorials and read up on the layout managers.
regarding, "I'm using Windowbuilder and that's the layout given when setting a container layout to absolute.": part of your problem, as you yourself admit, is that you don't yet fully understand Swing and in particular use of its layout managers, and one reason for this problem is that you're using a tool that buffers you from having to understand this. I urge you not to use WindowBuilder. Again read up on the layout managers and learn how to use them. You will not be sorry that you've done this.

Alignment of components in a gui window

I have got a window that looks like window1 and I would like it to look like window2:
This is my code:
String q = "Have you used GUI before?";
JLabel textLabel2 = new JLabel(
"<html><div style=\"text-align: center;\">" + q + "</html>", SwingConstants.CENTER);
add(textLabel2, BorderLayout.NORTH);
JPanel radioPanel = new JPanel();
add(radioPanel, BorderLayout.CENTER);
JPanel btnPanel = new JPanel();
add(btnPanel, BorderLayout.SOUTH);
For the radio-buttons, I tried to use GridLayout, but it broke the position of "Yes" and "No". And for the "back" and "next" buttons, horizontal alignment did not work (btnPanel.setAlignmentX(RIGHT_ALIGNMENT);), apparently. Any solutions will be highly appreciated, I'm stuck with this bit way too long. Thanks
--EDIT--
That is working perfectly fine:
btnPanel.setLayout(new BoxLayout(btnPanel, BoxLayout.LINE_AXIS));
btnPanel.setBorder(BorderFactory.createEmptyBorder(0, 10, 10, 10));
btnPanel.add(Box.createHorizontalGlue());
so the buttons problem is solved.
However, still can't get the radio-buttons fixed.
--EDIT 2--
Fixed the background for the radio-buttons using setOpaque(false);

What do you mean by it "broke" the position of "yes" and "no" as a GridLayout should work just fine. I'd give it 1 column and 2 (or 0 for variable number of) rows via new GridLayout(0, 1). Be sure that its opaque property is set as false by doing radioPanel.setOpaque(false);. This way it will show the background color of the container that it sits in. You may need to make the JRadioButtons non-opaque as well, I'm not sure.
Your btnPanel could use a BoxLayout and use Box.createGlue() to push the buttons over to the right side.
Most importantly -- if you haven't yet done so, please read the tutorials on use of the Swing layout managers which you can find here.

A couple of things you can do about this. You need to change your LayoutManager. This is not a great task for BorderLayout. You could do nested BoxLayouts. A vertical box that has the vertical fixed height strut, label, vertical fixed height strut, yes radio, vertical fixed strut, no radio, Vertical glue, and the final button panel. Then use your edit in the button panel to horizontally align them. That's one option, but the nesting of the panels is annoying.
Another option go get TableLayout and learn how to use it. TableLayout is one of the best LayoutManagers. It's easy to use, solidly tested, and it makes Swing fun again. You'll never use GridBagLayout ever ever ever again.
http://java.sun.com/products/jfc/tsc/articles/tablelayout/
The final option is use the new GroupLayout. I'm not terribly familiar with it, but it looks pretty easy. And, it doesn't take as much code or nesting unnecessary panels like Box does.

We Keep Coding

Java is a programming language and computing platform first released by Sun Microsystems in 1995.