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Adding JScrollPane to a JFrame

I want to add JPanel containers to a JScrollPane and add this scroll pane to a JFrame. But when I add multiple panels to the scroll pane this happens. The gap between the scroll pane and the top bar increases. I use BoxLayout as layout manager for all the components that I use.

Here is my take on laying out this GUI. Some notes:
Rather than use a BoxLayout in the JScrollPane it puts a GridLayout in the PAGE_START of a BorderLayout. This is fine for when it's OK to stretch the elements in the scroll pane to the full width of the GUI. Stick to a BoxLayout (which I rarely use) or a GridBagLayout if it's necessary to keep the elements at their preferred size.
This strategy of layout is basically 'divide and conquer' in that it starts with the smallest sub-divisions of the GUI (e.g. the FlowLayout for the buttons) and then adds those containers to larger containers with different layouts and constraints (e.g. adding that button panel to the LINE_END of a BorderLayout - to push I to the right of the GUI) as needed for the overall effect.
I'd also consider using a JList (using a panel for the renderer) in the scroll pane. It depends on the use as to whether that makes sense.
Note that this code is an MRE. An MRE should have everything that's needed (including imports, a class structure and the main method) for another person to compile and run the code.
import javax.swing.*;
import javax.swing.border.*;
import java.awt.*;
import java.awt.event.ActionEvent;
// ref: https://stackoverflow.com/a/70934802/418556
public class ScrollPaneTestGUI {
int elementCount = 1;
JPanel elementsPanel = new JPanel(new GridLayout(0,1,2,2));
public ScrollPaneTestGUI() {
initGUI();
}
private void initGUI() {
// this will become the content pane of the frame
JPanel gui = new JPanel(new BorderLayout(4,4));
gui.setBorder(new EmptyBorder(4,4,4,4));
JPanel pageStartPanel = new JPanel(new BorderLayout(2,2));
gui.add(pageStartPanel, BorderLayout.PAGE_START);
pageStartPanel.add(new JLabel("LINE START label"), BorderLayout.LINE_START);
// default flow layout is good for this one
JPanel buttonPanel = new JPanel();
pageStartPanel.add(buttonPanel, BorderLayout.LINE_END);
buttonPanel.add(new JButton("Does Nothing"));
Action addToScrollAction = new AbstractAction("Add to scrollPane") {
#Override
public void actionPerformed(ActionEvent e) {
elementsPanel.add(getPanelForScroll());
elementsPanel.revalidate();
}
};
JButton addToScrollButton = new JButton(addToScrollAction);
buttonPanel.add(addToScrollButton);
JPanel scrollPanel = new JPanel(new BorderLayout());
scrollPanel.add(elementsPanel, BorderLayout.PAGE_START);
gui.add(new JScrollPane(scrollPanel,
JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
JScrollPane.HORIZONTAL_SCROLLBAR_NEVER)
);
for (int ii=0; ii<2; ii++) {
elementsPanel.add(getPanelForScroll());
}
JFrame frame = new JFrame("ScrollPane GUI");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.setContentPane(gui);
frame.pack(); // sets the GUI to the exact size needed
frame.setMinimumSize(frame.getSize());
frame.setVisible(true);
}
private JPanel getPanelForScroll() {
JPanel p = new JPanel();
p.add(new JLabel("Panel " + elementCount++));
p.setBorder(new EmptyBorder(10,200,10,200));
p.setBackground(Color.GREEN);
return p;
}
public static void main(String[] args) {
Runnable r = new Runnable() {
#Override
public void run() {
new ScrollPaneTestGUI();
}
};
SwingUtilities.invokeLater(r);
}
}

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());

how can i set the size of two JPanel in one JFrame?

how can i modify the size of the panel in the JFrame
am doing a calculator, the first panel will hold the JTextField which i suppose to be small
the second panel will hold the JButtons which suppose to be bigger
JFrame frame = new JFrame(new GridLayout(2, 1));
JPanel panel1 = new JPanel();
JPanel panel2 = new JPabel();
frame.add(panel1);
frame.add(panel2);
i've been trying to make panel1 smaller than panel2 yet nothing worked!

GridLayout would not be an appropriate choice in this scenario since it ignores the preferred sizes of the components inside the container and displays them all at an equal size instead.
I'd suggest using a BorderLayout. You can find a demonstration and description of that layout manager as well as a few others in Oracle's tutorial, A Visual Guide to Layout Managers.
Here's another example using BorderLayout which might be more relevant to your problem.
import java.awt.*;
import javax.swing.*;
public class Test {
public static void main(String []args){
SwingUtilities.invokeLater(new Runnable() {
public void run() {
JFrame frame = new JFrame();
JPanel panel1 = new JPanel();
JPanel panel2 = new JPanel();
panel1.setBorder(BorderFactory.createTitledBorder("Panel 1"));
panel2.setBorder(BorderFactory.createTitledBorder("Panel 2"));
frame.add(panel1, BorderLayout.NORTH);
frame.add(panel2, BorderLayout.CENTER);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(new Dimension(200, 200));
frame.setVisible(true);
}
});
}
}
Edit: The JFrame's content pane uses a BorderLayout by default, hence the absence of a call to setLayout. Source

How to make this layout with Java swing?

I have the following layout:
The red, blue and green parts are JPanel. In the red part I have four JLabel. Now if I resize the JFrame, the title labels always stay in the center. But I would prefer if they are evenly distributed horizontaly in the red part. Which layout should I use for that?

Use a GridLayout(1, 0) for the top JPanel. The two numbers means 1 row and variable number of columns. If you are using JLabels, this will be sufficient, especially if you set the JLabels alignment constant to SwingConstants.CENTER. If you are using components that fill the grid slots, such as JButtons, then you may need to use other variants of the GridLayout constructor, such as GridLayout(1, 0, ?, 0) Where the ? is a number that tells the GridLayout how much horizontal separation there should be between slots.
The overall GUI would use a BorderLayout of course.
For more and better information on this, please check out Lesson: Laying Out Components Within a Container and A Visual Guide to Layout Managers
For example:
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridLayout;
import javax.swing.*;
public class LayoutEg {
private static void createAndShowGui() {
String[] labelStrings = {"One", "Two", "Three", "Four"};
JPanel topPanel = new JPanel(new GridLayout(1, 0));
for (String labelString : labelStrings) {
// create labels and center the text
topPanel.add(new JLabel(labelString, SwingConstants.CENTER));
}
topPanel.setBackground(Color.red);
JPanel centerPanel = new JPanel();
centerPanel.setBackground(Color.blue);
// setting preferred size for demonstration purposes only
centerPanel.setPreferredSize(new Dimension(700, 400));
JPanel bottomPanel = new JPanel();
bottomPanel.setBackground(Color.green);
// main panel uses BorderLayout
JPanel mainPanel = new JPanel(new BorderLayout());
mainPanel.add(centerPanel, BorderLayout.CENTER);
mainPanel.add(topPanel, BorderLayout.PAGE_START);
mainPanel.add(bottomPanel, BorderLayout.PAGE_END);
JFrame frame = new JFrame("LayoutEg");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}

Use a BorderLayout for the frame's content pane, and use a GridLayout with 1 row and four columns for the title panel.
See http://docs.oracle.com/javase/tutorial/uiswing/layout/border.html and http://docs.oracle.com/javase/tutorial/uiswing/layout/grid.html for tutorials.
If you don't want the same width assigned to each label, but in fact want the same space between every label, you may also use a BoxLayout, and add a glue between each label (and between the border of the panel and the label:
p.setLayout(new BoxLayout(p, BoxLayout.X_AXIS));
p.add(Box.createHorizontalGlue());
p.add(new JLabel("Label"));
p.add(Box.createHorizontalGlue());
p.add(new JLabel("Long Label"));
p.add(Box.createHorizontalGlue());
p.add(new JLabel("Very long Label"));
p.add(Box.createHorizontalGlue());
p.add(new JLabel("Extremely long Label"));
p.add(Box.createHorizontalGlue());

Use a BorderLayout for the main frame and use the NORTH, CENTER and SOUTH places.
To create empty space like in the bottom panel, use Box.createVerticalStrut(size).
Use BoxLayout to place the labels packed in a row.
Finally use GridBagLayout to center a panel in another Panel.
Here is a short example:
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridBagLayout;
import javax.swing.BorderFactory;
import javax.swing.Box;
import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
public class Prototype extends JFrame {
public Prototype() {
JPanel labelPanel = new JPanel();
labelPanel.setLayout(new BoxLayout(labelPanel, BoxLayout.LINE_AXIS));
labelPanel.add(new JLabel("First"));
labelPanel.add(Box.createHorizontalStrut(10));
labelPanel.add(new JLabel("Second"));
labelPanel.setBorder(BorderFactory.createEmptyBorder(4, 4, 4, 4));
labelPanel.setOpaque(false);
JPanel bottomPanel = new JPanel();
bottomPanel.add(Box.createVerticalStrut(15));
bottomPanel.setBackground(Color.GREEN);
JPanel centerPanel = new JPanel();
centerPanel.add(Box.createRigidArea(new Dimension(200, 300)));
centerPanel.setBackground(Color.BLUE);
JPanel northPanel = new JPanel(new GridBagLayout());
northPanel.add(labelPanel);
northPanel.setBackground(Color.RED);
JPanel panel = new JPanel(new BorderLayout());
panel.add(northPanel, BorderLayout.NORTH);
panel.add(centerPanel, BorderLayout.CENTER);
panel.add(bottomPanel, BorderLayout.SOUTH);
add(panel);
pack();
setDefaultCloseOperation(EXIT_ON_CLOSE);
setVisible(true);
}
public static void main(String[] args) {
new Prototype();
}
}

Use a MigLayout.
No, seriously, I used to go crazy trying to get Java layouts working. Then I started maintaining some software that uses MigLayouts, and after a week or so I could do anything I wanted. There is an excellent cheat sheet that looks pretty intimidating, but it's incredibly helpful.
With a MigLayout, to have evenly spread labels in a JPanel you would:
// the "fillx" means that the layout will expand to take up all available horizontal space
JPanel panel = new JPanel(new Miglayout("fillx"));
// the "growx" means that the component will expand to take up all available horizontal space
add(new JLabel("Work items"), "growx");
add(new JLabel("Change set"), "growx");
add(new JLabel("Files"), "growx");
add(new JLabel("Source code"), "growx");

gridLayout, put the labels into the grid layout and set rows to 1 and columns to 4 (1 row for each Label)
http://www.javabeginner.com/java-swing/java-gridlayout-class-example

GridBagLayout is one approach. Set the weightx value to 1.0.

For labels to be distributed evenly horizantally - in the red panel - use BoxLayout with X_AXIS direction and put 'glue' between each label - More here -
http://docs.oracle.com/javase/tutorial/uiswing/layout/box.html

problem in nested Jpanel over Jframe

I have a JFrame and a Jpanel over that in which various buttons are placed.so on click of a button I have called a new class which is also having containers placed in a Jpanel.so I want to show that new class panel over the main Jframe panel.How can I do that?
And if we use card layout in it then how can i use that as on click button i have called an object of a new class.
as
Card layout consider each component in a container as card and i want whole Jpanel as a card so is it possible to do that???
Can We do nesting of Jpanels in it?
Please suggest me a right way to do that?
here is SSCCE:
// this is the main class on which i want to use panel of other class
public class mymain
{
JFrame jframe = new JFrame();
JPanel panel = new JPanel();
BorderLayout borderlayout = new BorderLayout();
public mymain()
{
jframe.setLayout(borderlayout);
JMenuBar menubar = new JMenuBar();
jframe.setJMenuBar(menubar);
JButton home_button = new JButton("HOME");
menubar.add(home_button);
jframe.getContentPane().add(panel,BorderLayout.CENTER);
panel.setLayout(new GridBagLayout());
//here used containers over that frame
and call it from main()
}
here is another class to manage category is
public class manageCategory
{
JPanel panel = new JPanel();
GridBagLayout gridbglayout = new GridBagLayout();
GridBagConstraints gridbgconstraint = new GridBagConstraints();
public manageCategory()
{
panel.setLayout(new BorderLayout());
// i have again here used containers placed with grid bag layout
}
}
So now i want that as i click on home button used in mymain class then the panel that is used in manageCategory() should be displayed on the same panel.and when i again click on home button then the mymain panel get displayed.how can i do that???

I would advise you to use a CardLayout for this task.
Updated example with JPanel and "classes":
static class MainPanel extends JPanel {
public MainPanel(final Container frame) {
add(new JButton(new AbstractAction("Click to view next") {
#Override
public void actionPerformed(ActionEvent e) {
frame.add(new NextPanel(), "NextPanel");
((CardLayout) frame.getLayout()).show(frame, "NextPanel");
}
}));
}
}
static class NextPanel extends JPanel {
public NextPanel() {
add(new JLabel("Next page in the card layout"));
}
}
public static void main(String[] args) throws Exception {
JFrame frame = new JFrame("Test");
frame.setLayout(new CardLayout());
frame.add(new MainPanel(frame.getContentPane()), "MainPanel");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(400, 300);
frame.setVisible(true);
}

CardLayout is one of possible ways, but there are another options valid or required by most completed GUI
1) BorderLayout, because there only one JComponent can occupate decision area
someContainer.add(myPanel, BorderLayout.CENTER)
revalidate();
repaint();
2) GridBagLayout
before anything you have to get declared GridBagConstraints from myOldComponent layed by GridBagLayout
myContainer.setVisible(myOldComponent);
//or
myContainer.remove(myOldComponent);
myContainer.add(myNewComponent, gbc);
revalidate();
repaint();

You can
JFrame myFrame = new JFrame();
JPanel panel1 = new JPanel();
Panel1.setVisible(true);
myFrame.add(panel1);
JPanel panel2 = new JPanel();
Panel2.setVisible(false);
myFrame.add(panel2);
//Here you setup your panels and your actionlisteners etc and when
//you wish for your second panel to show up just run the code below.
panel1.setVisible(false);
panel2.setVisible(true);
Obviously you first have to add both panels to your Jframe. Panel1 will be at first visible, as it is the one shown by default. Panel2 must be set to be invisible in the beginning.