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Elements don't appear in a Panel with a GridLayout or FlowLayout, but with a setBounds they do

I'm doing a program that is composed by multiple panels in a JFrame.
I need to do every elements in differents classes (It's because in my school, we need to have every elements separeated in different classes for clean code), but every example that I see with my kind of problem, they do everything in one class.
And I think that my problem comes from having multile classes so I show you my classes.
I have a panel in wich I need to put 2 panel, here is the code :
public class Inscription extends JPanel{
private PanneauBoutons panneauBoutons = new PanneauBoutons();
private PanneauFormulaire panneauFormulaire = new PanneauFormulaire();
public Inscription(){
this.setLayout(new BorderLayout());
this.setBorder(BorderFactory.createLineBorder(Color.RED, 2));
this.add(panneauFormulaire,BorderLayout.CENTER);
this.add(panneauBoutons,BorderLayout.SOUTH);
this.setVisible(true);
}
}
And here is the Panel panneauFormulaire :
public class PanneauFormulaire extends JPanel{
private JLabel labelMatricule;
private JTextField zoneTexteMatricule;
public PanneauFormulaire(){
this.setLayout(new GridLayout(8,2,10,10));
this.setBorder(BorderFactory.createLineBorder(Color.black));
labelMatricule = new JLabel("Matricule : ");
this.add(labelMatricule);
zoneTexteMatricule = new JTextField(30);
this.add(zoneTexteMatricule);
this.setVisible(true);
}
So the problem Inscription don't appear on the main Frame if I don't do setBounds, but I want a BorderLayout...
(I tested and with a set bounds I can see the borders, so I think that it means the panel are really added to the Frame so why without setBounds I see anything?).
And the other problem is that the panel PanneauFormulaire don't appear on the Inscription panel...
So if I miss something, can you help me? thank you
And here it is the class that extends JFrame :
public class FenetrePrincipale extends JFrame {
private Container cont;
private Inscription inscriptionForm;
public FenetrePrincipale(){
super("IESN");
setBounds(100,100,1200,960);
getContentPane().setLayout(null);
setLocationRelativeTo(null);
setResizable(false);
...
inscription.addActionListener(new ActionListener(){
#Override
public void actionPerformed(ActionEvent e){
cont.removeAll();
inscriptionForm = new Inscription();
inscriptionForm.setOpaque(true);
cont.add(inscriptionForm);
invalidate();
repaint();
}
});

You should NOT be using a null layout and setBounds(). Swing was designed to be used with layout managers.
but when I click on an option in the menu, the current panel need to be change by another one,
Then you should be using a CardLayout.
Read the section from the Swing tutorial on How to Use CardLayout for working examples. So download the example and use it as the starting point of your project. The code will be better structured then what you currently have and it is easier to change working code than it is to fix broken code.

so why without setBounds I see anything?
That is because you set your layout to null in getContentPane().setLayout(null);.
Java containers comes with a default layout which you are allowed to set to a different one. How the components are arranged in the container are dependent on the layout you use. The layout will directly affects the location, alignment, spacing, dimension, preferredSize of the components.
However, if you choose not to use any layout (.setLayout(null)). Swing will not know how you want the components to be arranged, hence you see nothing in your content pane.
Since you wanted "absolute control" over the components, you will be expected to set the bounds (location and dimension) of each added component manually by yourself. This is why you are not seeing any components (even if you already added it) until you set the bounds for them.
Java, elements don't appear in a Panel with a GridLayout or FlowLayout, but with a setBounds they do
Every layout has their own characteristics and for some of them the order of your codes does makes a difference. Hence, I will advise you to go through what each layout can do for you. Then, depending on your needs, choose one (or a combination of a few) and study how to use it.
And here it is the class that extends JFrame :
You probably won't want to extends to a JFrame. You can always make a customized Container like JPanel and add it to the frame.
(Why would you want to paint your paintings on a frame instead of a piece of paper?)

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 use a variable in multiple jpanels?

I have a frame with a var , I added that var to a JPanel, and if I want to add the same var to another JPanel, it`s disappearing from the first JPanel. I want a logical explanation for my problem please, thank you !
I want to store my JLabel in both of my jpanels.
public class Gui {
JPanel panel1, panel2;
JLabel text = new JLabel("some text");
JFrame frame = new JFrame();
public Gui {
panel1 = new JPanel();
panel1.setLayout(null);
panel1.add(text);
panel1.getComponent(0).setBounds(50,50,50,50);
panel1.setBorder(BorderFactory.createLineBorder(Color.black));
panel1.setBounds(x,y,w,h);
// it`s working, the labels it`s visible
panel2 = new JPanel();
panel2.setLayout(null);
panel2.add(text);
panel2.getComponent(0).setBounds(100,100,50,50);
panel2.setBorder(BorderFactory.createLineBorder(Color.black));
panel2.setBounds(x,y,w,h);
//it`s not working, the label ins`t visible ...
frame.add(panel1);
frame.add(panel2);
}
}

Disclaimer: I am editing my answer in response to comments from the OP. However, I am still not entirely sure about some of the details of the question. I will gladly edit my answer as more clarifications are given.
Answer: One possible solution is to create subclasses of the Swing components you are using. For example,
public class MyPanel extends JPanel {
private JLabel label = new JLabel("some text");
public MyPanel() {
this.add(label);
}
}
Now you can create multiple instances of MyPanel which each have its own JLabel. Then you can add these panels to your frame.
Added: With the additional information given in the comments, I would go a step further and create a custom JFrame class:
public class MyFrame extends JFrame {
private MyPanel panel = new MyPanel();
public MyFrame() {
this.add(panel);
}
}
Now you can create several instances of MyFrame. If you want to go even further, you can add parameters to the constructors of both of these custom classes to set the JLabel text to different values in each instance MyFrame. I will leave the details as an exercise to the reader. (Of course, please ask if you get stuck, though.)

Just as it's discussed with in other posts. All Swing UI components (ie JLabel included) can only have one parent (ie JPanel). If you add it to another panel it will remove itself from the prior parent. There are very good reasons for this behavior. For example, JPanel 1 might not use the same Layout as JPanel 2 and hence the label would have to support two different placements within each JPanel. The whole point of using Objects as components is to provide encapsulation of data like (font, position within the parent, width, height, etc) inside that object. If you want two visual elements just create another element. Now that creates a problem "How do you synchronize the data across all of these controls?" That's basically scratching how do you build a proper Swing architecture for your program?
What you don't want to do is use the Swing component model (ie. Jabel, JTextField, etc) as your data model. And after reading your question and code I believe that's what you are doing. You may not realize it. UI Components should be used for display only. They reflect what is in the data model. So you'll want to create a model that doesn't involve Swing. It should model your problem regardless of how its displayed. That means you shouldn't assume it will always be Swing or web, etc.
There are very practical reasons for this. Say in a year you want to redesign your UI. If you combined the view components and data model together you pretty much have to start completely over. Even if you aren't switching technologies. Say you are switching from a JList to a JTable or a JTreeTable. Just simple changes of the types of components you have on the screen can be an absolute nightmare if you don't segment your view from the model. Plus the View displays thing, but the model might need information that isn't displayed to the user but is tied to what is being displayed. For example, the ID of the row in the database. If you stuff the view and data model together you have to play little hacks to store this invisible information in weird ways. Things that make it hard for other people to understand.
If you don't know what I mean you either will in 6 months when you have to make your first major redesign or you'll save yourself some pain now and try and understand what I mean now. Just simple POJOs will suffice. Then share those POJOs with your Swing components. For example:
MySpecialPanel panel1 = new MySpecialPanel();
MyOtherSPecialPanel panel2 = new MyOtherSpecialPanel();
frame.add( panel1 );
frame.add( panel2 );
...a little while later...
MySpecialPOJO specialPOJO = ...some call to a service...;
panel1.setSpecialPOJO( specialPOJO );
panel2.setSpecialPOJO( specialPOJO );
Notice that I created two subclasses of JPanel called MySpecialPanel and MyOtherSpecialPanel. Inside there they create the components contained within them. Then then expose a setter method taking a data model object of type MySpecialPOJO. Inside those methods we might see something like the following:
public void setSpecialPOJO( MySpecialPOJO specialPOJO ) {
this.model = specialPOJO;
textField1.setText( specialPOJO.getName() );
textField2.setText( specialPOJO.getDescription() );
radioButtonGroup.setSelected( specialPOJO.getGender() );
....
}
Now you have a way to take a model object, and update the relative UI components that make up that view. Notice it doesn't care about any other external dependencies (ie where it got the object from). It just updates the controls it owns to reflect what's carried by the POJO. Now if you follow these simple rules it makes instantiating your special panels easy. Whether you need only one instance or many instances. Also if you need to move panels within your program it's pretty easy to do that if you reduce your dependencies to just your POJOs. There's a lot more to this, but for now this will get you started. You still have to figure out how to get data out of the UI and back into your POJOs (events!). Controllers, Services, etc.
This might help you as well:
Up-to-date Swing MVC example + Question

You can't. As you noticed, a control can only be attached to one window at a time, and if you try to attach it to another one, it will remove itself from the first.
Suggestions:
panel2.add(text.clone()); // clone the existing label
panel2.add(new JLabel("some text")); // make a new label from scratch

how to display a JPanel inside a JScrollPane?

I am designing a Pizza Delivery simulator for a class project. My team and I have most of it done, but we are struggling with the GUI.
I need to be able to add items to the order. Each time I click the add item button, it creates a new AddItemPanel (a panel I created that extends JPanel), and adds it to the JScrollPane.
The problem I am running into is it will only add ONE AddItemPanel to the scrollPane. I am not sure if they are being hidden underneath the first one, or if I am just doing something stupid.
Here is the relevant code:
JPanel itemPanel = new JPanel(new GridLayout(0, 1));
JViewPort viewPort = new JViewport();
viewPort.setLayout(new GridLayout(0, 1)); // not sure if I need this line
JScrollPane scrollPane = new JScrollPane(viewPort);
itemPanel.add(scrollPane);
// other stuff
JButton addItemButton = new JButton("Add Item");
addItemButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
viewPort.add(new AddItemPanel());
validate();
}
});
So my questions are: Is this even possible with a JScrollPane? If so, how do I do it? If not, how would I accomplish something similar?
(PS. I have linked screen shots in case they are helpful in explaining.)
screen shot 1
screen shot 2

The best and most straightforward solution that I can think of is to use a JList or JTable that is held by the JScrollPane. These guys are a lot more flexible than I think you realize and can display fairly complex data if you use the right cell renderer. If you can't do this, then have the JScrollPane's viewport hold a JPanel that uses GridLayout. But don't mess with the viewport's layout.

You have to add a JPanel to the JScrollPane, then add the additional panels to that JPanel. The JScrollPanel can only manage one child.

Java Simple Question about working with JPanels

Just a quick question here. I have a program in which I need to create a number of JPanels, which will then each contain some objects (usually JLabels).
There are a few operations that I have to do each time i create a new JPanel, and I'm wondering if the order in which I do them has any bearing, or if there is a standard practice.
The operations I do are the following:
Declare the JPanel: JPanel panel = new JPanel(...)
Declare the JLabel: JLabel laberl = new JLabel...
Add the JPanel to some other content pane: frame.getContentPane().add(panel)
Set the bounds of the JPanel: panel.setBounds(...)
Add the JLabel to the JPanel: panel.add(label)

In general order isn't important as long as you add all the components to the panel and the panel is added to the content pane "before" you make the frame visible.
The standard practice is to use a layout manager, so there would be no need to set the bounds of the panel you added to the content pane.

The order doesn't matter. However, after creating and adding everything, you need to call revalidate() on the panel (or pack() on its parent window) so that the layout manager (I presume you're using one!) arranges the components as they should be.

Have a method createPanel() that returns the panel with all its children added.
Panel p = createPanel();
p.setBounds(...); // if you must
frame.getContentPane().add(p);
And then
Panel createPanel() {
Panel p = new Panel();
Label l = new Label("Heading");
p.add(l);
return p;
}
The order of constructing and adding items isn't important, except that when you add children, you should add them in the order you want them in the panel.