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JScrollPane not working correctly when adding JPanel (with FlowLayout) into JScrollPane

I tried to add a JPanel (with FlowLayout) to a JScrollPane but the ScrollBar is not working. I want to place buttons as grid but it places horizontally.
import javax.swing.*;
import java.awt.*;
public class Test {
public static void main(String[] args){
JFrame frame = new JFrame("Test");
frame.setVisible(true);
frame.setSize(1000,500);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel panel = new JPanel();
panel.setLayout(new FlowLayout(FlowLayout.LEFT));
JScrollPane pane = new JScrollPane(panel);
pane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
pane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
frame.add(pane);
for (int i=0;i<100;i++){
panel.add(new JButton("Label"));
}
}
}

I want to place buttons as grid but it places horizontally.
That's because you do not set the preferred size of the JPanel and because you add the JPanel to a JScrollPane you are effectively giving the JPanel infinite width and FlowLayout will lay out all its components in a single row until it reaches the width limit of the JPanel but because the width is infinite, all the JButtons appear on the same line. Also, because you set the horizontal scrollbar policy to NEVER, there is no way to scroll the JPanel.
You should call method setVisible(true) after you have added all the components.
Note that in the below code I use GridLayout rather than FlowLayout because FlowLayout will not display a grid of JButton. Also note that I call method pack() rather than method setSize().
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
public class Test {
public static void main(String[] args) {
JFrame frame = new JFrame("Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel panel = new JPanel();
panel.setLayout(new GridLayout(0, 10, 5, 5));
JScrollPane pane = new JScrollPane(panel);
pane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
pane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
for (int i=0;i<100;i++){
panel.add(new JButton("Label"));
}
frame.add(pane);
frame.pack();
frame.setVisible(true);
}
}
Here is a screen capture:
Note that, by default, JScrollPane will size itself so as to display all the JButtons. If you want the JScrollPane to only display a few rows, then you need to set its preferred size, for example
pane.setPreferredSize(new Dimension(710, 150));
EDIT
If you insist on using FlowLayout then you need to set the preferred size for both the JPanel and the JScrollPane.
import java.awt.Dimension;
import java.awt.FlowLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
public class Test {
public static void main(String[] args) {
JFrame frame = new JFrame("Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel panel = new JPanel();
panel.setPreferredSize(new Dimension(710, 315));
panel.setLayout(new FlowLayout(FlowLayout.LEFT));
for (int i = 0; i < 100; i++) {
panel.add(new JButton("Label"));
}
JScrollPane pane = new JScrollPane(panel);
pane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
pane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
pane.setPreferredSize(new Dimension(720, 160));
frame.add(pane);
frame.pack();
frame.setVisible(true);
}
}
Here is a screen capture.

Switch between different sized JPanels

To keep things short, I know how to switch between different JPanels using CardLayout and only using one JFrame but I want to know how, if it is possible, to have different sized JPanels occupying the JFrame. CardLayout uses the largest of the panels but I was wondering if there was any way to suppress that or override so that I could add different JPanels to a JFrame that were different sizes. Here is my code:
import java.awt.CardLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class View {
//Views
private JFrame frame;
private JPanel container;
private JPanel panel1;
private JPanel panel2;
private CardLayout layout;
private final int WIDTH = 1280;
private final int HEIGHT = 720;
public View(){
init();
frame = new JFrame();
frame.setResizable(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocationRelativeTo(null);
frame.add(container);
frame.pack();
frame.setVisible(true);
}
private void init(){
JButton button = new JButton();
layout = new CardLayout();
container = new JPanel(layout);
panel1 = new JPanel();
panel2 = new JPanel();
panel1.setBackground(Color.WHITE);
panel1.setPreferredSize(new Dimension(500, 500));
panel1.add(button);
panel2.setBackground(Color.BLACK);
panel2.setPreferredSize(new Dimension(500, 500));
container.add(panel1, "panel1");
container.add(panel2, "panel2");
button.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
layout.show(container, "panel2");
}
});
}
public static void main(String [] args){
View view = new View();
}
}
I put the JButton in the init method because I need it for future use and wanted to make sure now that it could be done.

For a quick solution try two separate JFrames, or resize the frame to the size of the panel on button press.

The only way it seems to work with the cardLayout is by setting the preferred size of the container panel after the button is clicked.
button.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
layout.show(container, "panel2");
container.setPreferredSize(new Dimension(100, 100));
frame.pack();
}
});
It's not a very great solution but it's pretty simple.
If a login window is what you need I would definitely recommend using 2 frames, just seems more logical.

You can't use a CardLayout. So you need to manage the visible panel yourself.
The logic would be something like:
JPanel content = (JPanel)frame.getContentPane();
content.removeAll();
content.add( theOtherPanel );
frame.pack();
So the idea is you only have one panel added to the content pane at a time and you need to swap it by doing the remove and add before you pack the frame so the frame is displayed at the size of each panel.
The question is why do you want to do this? Users don't like to see the size of the frame continually changing.

Using JLayeredPane to add multiple JPanels to a JPanel

I am trying to add multiple panels to another panel. I want them to be on top of each other so I'm using JLayeredPane. I've added a button to each one. Two buttons should appear when it works.
import java.awt.Color;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLayeredPane;
import javax.swing.JPanel;
public class PanelTest {
public static void main(String[] args) {
JFrame frame = new JFrame();
JPanel mainPanel = new JPanel();
JPanel panel1 = new JPanel();
JPanel panel2 = new JPanel();
JLayeredPane layers = new JLayeredPane();
mainPanel.add(layers);
panel2.setOpaque(false);
panel1.setOpaque(false);
panel1.setVisible(true);
panel2.setVisible(true);
panel1.add(new JButton("1111111111"));
panel2.add(new JButton("2"));
frame.setContentPane(mainPanel);
layers.add(panel1, new Integer(2));
layers.add(panel2, new Integer(3));
frame.setVisible(true);
frame.setSize(500, 500);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
}
Only the grey background of the mainPanel is visible. What am I doing wrong?

When adding a component to a JLayeredPane, you're essentially adding the component to a null layout using container. This means that you must fully specify both the component's size and its position, often solving both with a setBounds(...) call. Call this on panel1 and panel2, for example:
panel1.setBounds(10, 10, 100, 100);
panel2.setBounds(70, 70, 100, 100);
Edit:
setting bounds didn't make any difference
Setting the size (bounds) is required but you still have an additional problem.
You are adding the JLayeredPane to a JPanel which uses a FlowLayout. By default a FlowLayout respects the preferred size of the component added to it. Since JLayeredPane uses a null layout its preferred size is (0, 0) so there is nothing to paint.
Two solutions:
You don't need the JPanel, just use: frame.setContentPane(layers);
If you really want to use the panel then you need to change the layout manager: JPanel mainPanel = new JPanel( new BorderLayout());

JLayeredPane white background next to component

Experimenting with layered panes here and I'm having a problem. I have two JPanels. I'm adding them both to a JLayeredPane - panel1 is big enough to take up the whole space, while panel2 is smaller and centered using FlowLayout. The problem is that with JLayeredPane, the background next to panel2 seems to be painted white when I add it. Here's a picture to illustrate. panel1 is blue, panel2 is red:
As you can see, the bottom part of the panel1 is still painted, but for some reason the sides are just white. The panel2 is 700 pixels wide and centered, while the frame is 800 pixels wide, so it's definitely not a problem with that. Here's the entire class:
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import javax.swing.JFrame;
import javax.swing.JLayeredPane;
import javax.swing.JPanel;
public class Errortest extends JFrame {
public static void main(String[] args) {
//Creating frame and setting the JLayeredPane as contentpane
Errortest frame = new Errortest();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JLayeredPane pane = new JLayeredPane();
pane.setLayout(new FlowLayout(FlowLayout.CENTER, 0, 0));
pane.setPreferredSize(new Dimension(800,600));
frame.setContentPane(pane);
frame.pack();
//Creating panels
JPanel panel1 = new JPanel();
panel1.setPreferredSize(new Dimension(800,600));
panel1.setBackground(Color.BLUE);
JPanel panel2 = new JPanel();
panel2.setPreferredSize(new Dimension(700,500));
panel2.setBackground(Color.RED);
pane.add(panel1, new Integer(0));
pane.add(panel2, new Integer(1));
frame.setVisible(true);
}
}
Hopefully that wasn't too confusing. From what I can tell, the white background comes from the JFrame itself, since when I do frame.setBackground(Color.YELLOW); it turns yellow.

If you add a component to a JLayeredPane, it's like adding it to a null layout using container: you must fully specify the component's size and position.
import java.awt.*;
import javax.swing.*;
public class ErrorTest extends JFrame {
public static void main(String[] args) {
// Creating frame and setting the JLayeredPane as contentpane
ErrorTest frame = new ErrorTest();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JComponent pane = new JLayeredPane();
//pane.setLayout(new FlowLayout(FlowLayout.CENTER, 0, 0)); // Take out FlowLayout
pane.setPreferredSize(new Dimension(800, 600));
frame.setContentPane(pane);
// Creating panels
JPanel panel1 = new JPanel();
panel1.setBackground(Color.BLUE);
panel1.setBounds(0, 0, 800, 600); // <<<---- Set Bounds
JPanel panel2 = new JPanel();
panel2.setBackground(Color.RED);
panel2.setBounds(50, 0, 700, 500); // <<---- Set Bounds
pane.add(panel1, new Integer(1));
pane.add(panel2, new Integer(2));
frame.pack();
frame.setVisible(true);
}
}

I believe I found out what the problem is. Has to do with the answer here:
JLayeredPane not respecting layers
You need a layout manager which understands the Z-Axis. The default layout managers don't understand the Z-Axis of the JLayeredPane.
So it's the FlowLayout that's messing me up. I'll just use absolute positioning for my project and use setBounds() to make sure the red panel ends up in the middle. Otherwise I'd have to look into custom layout managers I suppose.

JScrollPane inside JLayeredPane no repaint?

This could be something very simple but I'm totally confused.
I have a JScrollPane inside a JLayeredPane when I scroll in the pane the things above in the JLayeredPanedoesn’t get repainted at all.
Here I got a small example notice how the blue square doesn’t get repainted at all.
Have I completely misunderstood how the layered pane works?
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import javax.swing.JFrame;
import javax.swing.JLayeredPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
public class LayeredTest extends JPanel{
public LayeredTest(){
JPanel content = new JPanel();
content.setBackground(Color.red);
content.setPreferredSize(new Dimension(2048, 2048));
content.setBounds(0, 0, 2048, 2048);
JPanel control = new JPanel();
control.setBackground(Color.blue);
control.setPreferredSize(new Dimension(200, 50));
control.setBounds(0, 0, 100, 50);
JScrollPane scroll = new JScrollPane(content);
scroll.setBounds(0, 0, 400, 400);
JLayeredPane layeredPane = new JLayeredPane();
layeredPane.setPreferredSize(new Dimension(400, 400));
layeredPane.add(control, 0);
layeredPane.add(scroll, 1);
this.add(layeredPane, BorderLayout.CENTER);
}
public static void main(String[] args) {
//Create and set up the window.
JFrame frame = new JFrame("Test - Very lulz");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocation(100, 100);
frame.setSize(400, 400);
//Create and set up the content pane.
frame.setContentPane(new LayeredTest());
//Display the window.
frame.pack();
frame.setVisible(true);
}
}
Any ideas?

What you are doing is adding the components control and scroll to the "default" layer, so in effect they are still on the same layer. To put them on different layers, you need to specify the layer number as well. It's best to place the components somewhere between the default layer (which is the bottom-most with an index of 0) and the next layer, which is the "palette" layer with an index of 100.
So, to put the components on layers 50 and 51, for example, change where you're adding the components to layeredPane to:
layeredPane.add(scroll, 50, 0);
layeredPane.add(control, 51, 0);
This will place scroll at position 0 on layer 50, and control at position 0 on layer 51.