Develop Reference

Is there a way to put JPanel on a JPanel?

I'm trying to put a JPanel inside OR on a JPanel, whichever may be the case, ultimately I just want this to work like this
As you can see on the picture, the red line is a JFrame and it has 2 JPanels inside it, on the green JPanel there are some different JPanels.
I need help with the green JPanel and the little JPanels inside it. Is there any way to make it work like this?
Any help would be greatly appreciated!
==============EDIT 1==============
So here is some code, to show you what I've done so far with the help of #hfontanez.
import javax.swing.*;
import java.awt.*;
import java.io.IOException;
public class Main
{
public static void main(String[] args)
{
//JFrame
JFrame jframe = new JFrame();
jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
jframe.setSize(1920, 1080);
jframe.setResizable(false);
jframe.setLocationRelativeTo(null);
jframe.setVisible(true);
//parentJpanel - This is the main panel
JPanel parentJpanel = new JPanel();
parentJpanel.setBackground(Color.YELLOW);
parentJpanel.setSize(1920, 1080);
parentJpanel.setLayout(new BorderLayout());
//smallPanel - This is the little panel on the bottom
JPanel smallPanel = new JPanel();
smallPanel.setBackground(Color.GREEN);
smallPanel.setSize(1920, 300);
smallPanel.setLocation(0, 780);
smallPanel.setLayout(new BoxLayout(smallPanel, BoxLayout.PAGE_AXIS));
parentJpanel.add(smallPanel);
jframe.add(parentJpanel);
}
}
I expected the top part to be yellow, and the small part on the bottom to be green, yet the whoel thing turned green. What did I do wrong?

The pictured GUI is created using three panels.
The YELLOW panel is the game play area. It has no layout, no components (which define their own preferred sizes) and is custom painted, so it defines a sensible preferred size to report to the layout manager.
The GREEN panel contains controls. It uses a FlowLayout.
The RED panel uses a BorderLayout, and puts the YELLOW panel in the CENTER and the GREEN panel in the PAGE_END.
Code
This is the code that made the screenshot seen above.
import javax.swing.*;
import javax.swing.border.EmptyBorder;
import java.awt.*;
public class GameLayout {
GameLayout() {
// The main GUI. Everything else is added to this panel
JPanel gui = new JPanel(new BorderLayout(5, 5));
gui.setBorder(new EmptyBorder(4, 4, 4, 4));
gui.setBackground(Color.RED);
// The custom painted area - it is a panel that defines its preferred size.
gui.add(new GamePanel());
JPanel buttonPanel = new JPanel(new FlowLayout(FlowLayout.LEADING));
buttonPanel.setBackground(Color.GREEN);
for (int ii = 1; ii<5; ii++) {
buttonPanel.add(new JButton("B " + ii));
}
gui.add(buttonPanel,BorderLayout.PAGE_END);
JFrame f = new JFrame("Game Layout");
f.setContentPane(gui);
f.setLocationByPlatform(true);
f.pack();
f.setVisible(true);
}
public static void main(String[] args) {
Runnable r = () -> new GameLayout();
SwingUtilities.invokeLater(r);
}
}
class GamePanel extends JPanel {
GamePanel() {
setBackground(Color.YELLOW);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(400, 100);
}
}

You need to use a LayoutManager so when you put the JPanel inside the other JPanel it will have the correct look. If you simply put panels inside the others, the parent JPanel will use its default layout manager, which is FlowLayout.
For the look of it, it seems you need to use Border Layout for the parent (yellow) panel. For the green, you have options, but I think your best bet is to use Box Layout with a PAGE_AXIS Component Orientation.
In general, you need to be familiarized with two things: 1) Layout Managers and how they behave, and 2) the default layout behavior of JComponents.

How can I display 2 different panels at the same time?

My first panel's layout is BorderLayout and my second panel's layout is GridBagLayout. I don't know how to show them both at the same time.
I already tried adding two panels to on another panel.

Adding both to another panel is the way to go! But you have to make the right choice of LayoutManager for this "parent" panel. Let me give you an example:
The JFrame's content pane (where you add all your Components to) can be setup with a LayoutManager of your choice. See this runnable example, which creates two JPanels of 100x100 pixels in different colors. The panels are using the LayoutManagers you mentioned, but the main content pane of the JFrame is set to a BoxLayout (horizontal, but you can also set it to vertical!).
You can do this to any other panel, too. A panel.setLayout(new BoxLayout(panel, BoxLayout.X_AXIS)); is enough. The below example just uses the content pane, but you can adapt it to your needs:
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridBagLayout;
import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class TwoPanels extends JFrame {
private static final long serialVersionUID = 1L;
private static final Dimension DEFAULT_DIMENSION = new Dimension(100, 100);
public static void main(String[] args) {
new TwoPanels();
}
public TwoPanels() {
//create panel 1
JPanel panel1 = new JPanel(new BorderLayout());
panel1.setPreferredSize(DEFAULT_DIMENSION);
panel1.setBackground(Color.RED);
//create panel 2
JPanel panel2 = new JPanel(new GridBagLayout());
panel2.setPreferredSize(DEFAULT_DIMENSION);
panel2.setBackground(Color.GREEN);
//set content pane layout
setLayout(new BoxLayout(this.getContentPane(), BoxLayout.X_AXIS));
//add to content pane
add(panel1);
add(panel2);
//setup and display window
pack();
setVisible(true);
}
}
It looks like this:
EDIT: It's a little unclear from your question that you actually want to stack overlaying panels. You might find what you need here: https://docs.oracle.com/javase/tutorial/uiswing/components/layeredpane.html

JLabel too wide

I wrote the following code which is a simple window with a JLabel header at the top. The code is as follows:
import java.awt.Color;
import java.awt.Font;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingConstants;
public class Main extends JFrame {
private static final long serialVersionUID = 1L;
public static void main(String[] args) {
init();
}
public Main() {
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
int WIDTH = 500;
int HEIGHT = 500;
setBackground(Color.LIGHT_GRAY);
setSize(WIDTH, HEIGHT);
setTitle("New Window");
setLocationRelativeTo(null);
JPanel pane = new JPanel();
pane.setOpaque(false);
setContentPane(pane);
pane.setLayout(null);
JLabel title = new JLabel("New Window", SwingConstants.CENTER);
title.setFont(new Font("Neuropol", Font.PLAIN, 22));
title.setSize(WIDTH, 20);
title.setBorder(BorderFactory.createLineBorder(Color.black));
pane.add(title);
}
static void init() {
Main frame = new Main();
frame.setVisible(true);
}
}
I'm having a weird issue with it though. As you can see I set the width of the JLabel to the same width as the JFrame (and therefore the same width as the JPanel), but for some reason, the label goes past the right edge of the Frame. The width of the frame is 500, but I have to set the JLabel to a width of 483 in order for the border to be within the JFrame. I've been over and over this, but can't see anything wrong. Does anybody see my mistake here?

I set the width of the JLabel to the same width as the JFrame
But the JFrame width includes the "decorations" of the frame, like the Border.
I have to set the JLabel to a width of 483 in order for the border to be within the JFrame.
No, 483 will make the label too big for the frame. The Borders of the frame are not 17 pixels. I think the Borders are 4 or 5 pixels each depending on the LAF.
So this is another reason why you should NOT be using a null layout as hardcoding a value for one LAF may not work on another LAF.
Also, what happens if the user resizes the frame wider? Now the label will not go to the end. Use a Layout Manager do design dynamic GUI's that adapt to changes as the user resizes the frame.
The easiest solution is to just use the default BorderLayout of content pane of the frame. Then you add your label to the PAGE_START.
add(title, BorderLayout.PAGE_START);
There is also no reason to create a content pane. The frame already has a JPanel which uses a BorderLayout.
Read the Swing tutorial on Layout Managers for more information and working examples. Download the demos code and use them as a starting point for your code. The demo code will show you how to better structure your code to follow Swing conventions.

Simple GUI Java layout issue

I'm trying to do the following and I'm not sure what type of Java layout to use.
I want a JFrame with a single panel totalPanel. totalPanel should contain two panels which are custom classes I write, PanelA and PanelB. PanelA starts out with height 200 and PanelB starts out with height 400. When the user expands the window or resizes the window, only PanelB should increase in height, but both panels can increase in width.
How can I set this up? I've tried to use BorderLayout but then "North" is always too small in height. I've tried to use BoxLayout but then both PanelA and PanelB are always the same height.

Consider having totalPanel use a BorderLayout. Add the PanelA to the BorderLayout.PAGE_START position and the PanelB to the BorderLayout.CENTER position.
For more on the layout managers, please review the tutorial: Lesson: Laying Out Components Within a Container
Edit: I see that you've used BorderLayout, that it "doesn't work" but you don't show code. For more fine tuning on why it doesn't work, consider showing us code.
To get it to work consider giving your PanelX classes getPreferredSize() overrides that would help set the initial sizes of the JPanels.
For example:
import java.awt.BorderLayout;
import java.awt.Dimension;
import javax.swing.*;
public class SimpleGuiLayout {
private static void createAndShowGui() {
JPanel totalPanel = new JPanel(new BorderLayout());
totalPanel.add(new PanelX(800, 200, "Panel A"), BorderLayout.PAGE_START);
totalPanel.add(new PanelX(800, 400, "Panel B"), BorderLayout.CENTER);
JFrame frame = new JFrame("Simple Gui Layout");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(totalPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
class PanelX extends JPanel {
private int prefW;
private int prefH;
public PanelX(int prefW, int prefH, String title) {
this.prefW = prefW;
this.prefH = prefH;
setBorder(BorderFactory.createTitledBorder(title));
}
#Override
public Dimension getPreferredSize() {
return new Dimension(prefW, prefH);
}
}
If run, it would look like so:
And would resize appropriately.

One approach (probably not the simplest) would be a GridBagLayout.
Use the weightx and weighty constraints to control which members can resize.

I recommend a GridBagLayout. It is complex to use, but it can solve your problem. Assuming panelA is on top of panelB, you would have the following constraints:
panelA and panelB's gridx would be 0
panelA would be ad gridy 0, and panelB at gridy 1
for both, you would set fill = BOTH
but to have only panelB increase in height, you would set panelB's weighty to 1.0, and panelA's to 0

You originally solution using BorderLayout will work already, you just need to set preferred height of panelA:
panelA.setPreferredSize(new Dimension(0, 200));
The width doesn't matter because BorderLayout will ignore preferred width of component added to NORTH or SOUTH.

How to Correctly Set Minimum Sizes in Java?

For a GUI application I am creating in Java, I have the following:
A JFrame, set to have a minimum size of (300,200)
A JSplitPane, in which lies:
On the left, a JScrollPane (containing a JTree) with a minimum size of (100,0) (I only want to restrict the width to 200)
On the right, a JPanel with a minimum size of (200,0)
The sizing does not give me any issue under the following conditions:
Resizing the JSplitPane all the way to the left (to the JScrollPane's minimum size), and subsequently resize the window afterward
Just resizing the window, to a certain degree
The problem occurs when I move the JSplitPane too close to the right, whereupon resizing the window the JPanel in the right of the JSplitPane fails to adhere to the minimum width I set.
I attempted setting a maximum width on the JScrollPane, which did not seem to help at all.
Is there something involving maximum sizes I must do? Or perhaps there is a way to attach a Listener to one of the panels to force my desired behavior? Ultimately, I just want the right panel in the JSplitPane to never be less than 200px wide.
Here is an example with behavior I am experiencing:
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.GridLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JSplitPane;
import javax.swing.JTree;
public class ResizeTest
{
private JFrame frame;
public static void main(String[] args)
{
EventQueue.invokeLater(new Runnable()
{
public void run()
{
try
{
ResizeTest window = new ResizeTest();
window.frame.setVisible(true);
}
catch(Exception e)
{
e.printStackTrace();
}
}
});
}
public ResizeTest()
{
initialize();
}
private void initialize()
{
frame = new JFrame();
frame.setMinimumSize(new Dimension(300, 200));
frame.setBounds(100,100,450,300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().setLayout(new GridLayout(0, 1, 0, 0));
JSplitPane splitPane = new JSplitPane();
frame.getContentPane().add(splitPane);
JScrollPane scrollPane = new JScrollPane();
scrollPane.setMinimumSize(new Dimension(100, 0));
splitPane.setLeftComponent(scrollPane);
JTree tree = new JTree();
tree.setMinimumSize(new Dimension(100, 0));
scrollPane.setViewportView(tree);
JPanel panel = new JPanel();
panel.setMinimumSize(new Dimension(200, 0));
splitPane.setRightComponent(panel);
}
}
Update:
I'm afraid I don't fully understand the point trying to be made in the proposed solutions, except for that setPreferred() and setMinimum/Maximum() are better to be avoided.
My question in response to learning this is, what are my options for restricting the JSplitPane divider outside of using these methods? MadProgrammer mentioned listening for the componentResized event, but I need just a little more clarification as to why. Am I calling setDividerLocation() in response to this event?
I apologize in advance if the appended question is meant as a separate StackOverflow question entirely, I can post another and link here if necessary.
Update 2:
Is simply not regulating how the user chooses to size the window and having the right panel in a JScrollPane a viable option? This looks to me like somewhat of a standard practice.

Firstly, the method setMinimumSize is a suggestion to the LayoutManager API. A suggestion that may be ignored.
In order to be able to even come close to supporting this, you will need to use something like a ComponentListener and monitor the componentResized event.
The best solution I can think of is to use a LayoutManager that actually uses the minimum and maximum size constraints, something like GridBagLayout.
Use this on a "content" pane and place you're JSplitPane onto this (setting it's minimum and maximum size accordingly) then add the "content" pane to frame.
UPDATE
Sorry, I'm probably missing something really obvious, but I put this little test together, I hope it has some ideas that help :P
public class TestFrameSize extends JFrame {
public TestFrameSize() throws HeadlessException {
setDefaultCloseOperation(EXIT_ON_CLOSE);
setSize(600, 600);
setLocationRelativeTo(null);
setMinimumSize(new Dimension(250, 250));
JLabel left = new JLabel("Left");
JLabel right = new JLabel("Right");
Dimension pSize = new Dimension(100, 100);
Dimension mSize = new Dimension(25, 100);
left.setPreferredSize(pSize);
left.setMinimumSize(mSize);
right.setPreferredSize(pSize);
right.setMinimumSize(mSize);
JSplitPane pane = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT, left, right);
JPanel content = new JPanel(new GridBagLayout());
content.add(pane);
setLayout(new BorderLayout());
add(content);
}
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
new TestFrameSize().setVisible(true);
}
}

In this example, the preferred size of the content of a JSplitPane is initially set to a small multiple of the component's preferred size in getPreferredSize(). Note that the JSplitPane will become no smaller than the panel's minimum size, managed by the enclosed Jlabel.