Develop Reference

Repaint method not working on JComponent java swing

I want to have a text field to input an integer, then select 1) Grow or 2) Shrink, and then click the button so that the circle gets redrawn on the screen based on the selected options.
I don't know why it isn't repaining. (Don't worry about the layout, just want to get it to work first)
My Frame:
public class Main {
public static void main(String[] args) {
var frame = new JFrame();
frame.setSize(400,400);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
var circleComp = new circleComponent();
var panel1 = new JPanel();
var multiplierLabel = new JLabel("Grow Multiplier");
var multiplierField = new JTextField(20);
var radio1 = new JRadioButton("Grow Circle");
var radio2 = new JRadioButton("Shrink Circle");
var bg = new ButtonGroup();
bg.add(radio1);
bg.add(radio2);
JButton button = new JButton("Rivizato");
button.addActionListener(
new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
if(radio1.isSelected()){
rrComp.repaint(0,0,Integer.parseInt(multiplierField.getText())*rrComp.getWidth(), Integer.parseInt(multiplierField.getText())*rrComp.getHeight());
}
else if(radio2.isSelected()){
rrComp.repaint(0,0,Integer.parseInt(multiplierField.getText())/rrComp.getWidth(), Integer.parseInt(multiplierField.getText())/rrComp.getHeight());
}
}
}
);
panel1.add(multiplierLabel);
panel1.add(multiplierField);
panel1.add(button);
panel1.add(radio1);
panel1.add(radio2);
frame.add(panel1);
frame.add(circleComp);
}
}
My CircleComponent class:
public class CircleComponent extends JComponent {
public void paintComponent(Graphics g){
super.paintComponent(g);
var g2 = (Graphics2D) g;
var circle = new Ellipse2D.Double(0,0,100,100);
g2.draw(circle);
}
}

var circle = new Ellipse2D.Double(0,0,100,100); means that your circle will never change size.
You should also be careful with repaint(x, y, width, height) as it could leave regions of your component "dirty". Better to just use repaint.
As a conceptual example...
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.Ellipse2D;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public final class Main {
public static void main(String[] args) {
new Main();
}
public Main() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new JFrame();
frame.add(new MainPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class MainPane extends JPanel {
private CirclePane circlePane;
public MainPane() {
setLayout(new BorderLayout());
JPanel actionsPane = new JPanel(new GridBagLayout());
JButton growButton = new JButton("Grow");
growButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
circlePane.grow();
}
});
JButton shrinkButton = new JButton("Shrink");
shrinkButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
circlePane.shrink();
}
});
actionsPane.add(growButton);
actionsPane.add(shrinkButton);
circlePane = new CirclePane();
add(circlePane);
add(actionsPane, BorderLayout.SOUTH);
}
}
public class CirclePane extends JPanel {
private Ellipse2D circle;
public CirclePane() {
circle = new Ellipse2D.Double(0, 0, 100, 100);
}
public void grow() {
double width = circle.getWidth() + 10;
double height = circle.getHeight() + 10;
circle.setFrame(0, 0, width, height);
repaint();
}
public void shrink() {
double width = Math.max(0, circle.getWidth() - 10);
double height = Math.max(0, circle.getHeight() - 10);
circle.setFrame(0, 0, width, height);
repaint();
}
#Override
public Dimension getPreferredSize() {
return new Dimension(400, 400);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
double x = (getWidth() - circle.getWidth()) / 2d;
double y = (getHeight() - circle.getHeight()) / 2d;
g2d.translate(x, y);
g2d.draw(circle);
g2d.dispose();
}
}
}
nb: I know I've not used JTextField to specify the size of the circle, that's on purpose. You will need to adapt your requirements to work in a similar way - can you see where you might pass parameters to the CirclePane?

Java Swing: Trying to get a button to center

I'm trying to make a login page for an idea I'm working on and am trying to center two buttons. When I get the screen dimensions and divide them by 2 it is not centered. Here's my code:
import javax.swing.*;
import java.awt.*;
public class ChatWindow extends JFrame {
public ChatWindow() {
JFrame frame = new JFrame("EasyChat");
JButton login = new JButton("Login");
JButton signup = new JButton("Don't have an account? Sign Up");
JPanel mainPanel = new JPanel();
Dimension ss = Toolkit.getDefaultToolkit().getScreenSize();
frame.setVisible(true);
frame.setLayout(null);
frame.setSize(800,450);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
frame.getContentPane().add(login);
frame.getContentPane().add(signup);
login.setPreferredSize(new Dimension(25,60));
login.setFont(new Font("HelveticaNeue", Font.BOLD, 20));
signup.setBounds(ss.width / 2, ss.height / 2 + 125, 200, 100);
login.setBounds(ss.width / 2, ss.height / 2, 200, 100);
mainPanel.setLayout(new BorderLayout());
mainPanel.setBorder(BorderFactory.createEmptyBorder(0, 10, 10, 10));
}
}
I also want to know how to make the buttons stayed centered if the user exits fullscreen mode.
Thank you.

Make use of the available layout managers. See Laying Out Components Within a Container for more details
For simplicity, I've just use GridBagLayout as this will centre the components within the container by default
And you get resisability for free
import java.awt.EventQueue;
import java.awt.GridBagLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
public class Test {
public static void main(String[] args) {
new Test();
}
public Test() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new JFrame();
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
public TestPane() {
setBorder(new EmptyBorder(16, 16, 16, 16));
setLayout(new GridBagLayout());
add(new JButton("Login"));
add(new JButton("Sign Up"));
}
}
}
Now, if you want the buttons to be the same, you might be able to get it to work using something like GridLayout,
import java.awt.EventQueue;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
public class Test {
public static void main(String[] args) {
new Test();
}
public Test() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new JFrame();
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
public TestPane() {
setBorder(new EmptyBorder(32, 32, 32, 32));
setLayout(new GridBagLayout());
JPanel buttonPane = new JPanel(new GridLayout(1, -1));
buttonPane.add(new JButton("This is a long button"));
buttonPane.add(new JButton("Sign Up"));
add(buttonPane);
}
}
}
Or you could use a custom layout manager, for example...
import java.awt.Component;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Insets;
import java.awt.LayoutManager2;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
public class Test {
public static void main(String[] args) {
new Test();
}
public Test() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new JFrame();
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
public TestPane() {
setBorder(new EmptyBorder(32, 32, 32, 32));
setLayout(new ButtonLayoutManager());
add(new JButton("This is a long button"));
add(new JButton("Sign Up"));
}
}
public class ButtonLayoutManager implements LayoutManager2 {
private int horizontalPadding = 0;
#Override
public void addLayoutComponent(Component comp, Object constraints) {
}
#Override
public void addLayoutComponent(String name, Component comp) {
}
#Override
public void removeLayoutComponent(Component comp) {
}
#Override
public void invalidateLayout(Container target) {
}
#Override
public Dimension maximumLayoutSize(Container target) {
return preferredLayoutSize(target);
}
#Override
public Dimension minimumLayoutSize(Container parent) {
return preferredLayoutSize(parent);
}
#Override
public Dimension preferredLayoutSize(Container parent) {
int height = 0;
int width = 0;
for (Component comp : parent.getComponents()) {
height = Math.max(comp.getPreferredSize().height, height);
width = Math.max(comp.getPreferredSize().width, width);
}
width = (width * parent.getComponentCount()) + (horizontalPadding * parent.getComponentCount() - 1);
Insets insets = parent.getInsets();
width += insets.left + insets.right;
height += insets.top + insets.bottom;
return new Dimension(width, height);
}
#Override
public float getLayoutAlignmentX(Container target) {
return 0.5f;
}
#Override
public float getLayoutAlignmentY(Container target) {
return 0.5f;
}
#Override
public void layoutContainer(Container parent) {
int width = parent.getWidth();
int height = parent.getHeight();
Insets insets = parent.getInsets();
int maxWidth = 0;
int maxHeight = 0;
for (Component comp : parent.getComponents()) {
maxWidth = Math.max(comp.getPreferredSize().width, maxWidth);
maxHeight = Math.max(comp.getPreferredSize().height, maxHeight);
}
int padding = (horizontalPadding * parent.getComponentCount() - 1);
int totalWidth = padding + (maxWidth * parent.getComponentCount());
int yOffset = (height - maxHeight) / 2;
int xOffset = (width - totalWidth) / 2;
for (Component comp : parent.getComponents()) {
comp.setBounds(xOffset, yOffset, maxWidth, maxHeight);
xOffset += horizontalPadding + maxWidth;
}
}
}
}
nb: I've not done extensive testing on this and is only meant for demonstration purposes

This answer seems to use the (first) approach detailed by MadProgrammer, but since I have it ready.
import java.awt.*;
import javax.swing.*;
import javax.swing.border.EmptyBorder;
public class CenteredButtons {
public CenteredButtons() {
JFrame f = new JFrame("Centered Buttons");
// A FlowLayout might also be used here
// Doing so would allow each button to be its natural size
JPanel buttonPanel = new JPanel(new GridLayout(1,0,20,20));
buttonPanel.add(new JButton("Yes"));
buttonPanel.add(new JButton("No"));
buttonPanel.setBorder(new EmptyBorder(30,75,30,75));
// a component (e.g. buttonPanel) added with no constraints will be centered
JPanel centerPanel = new JPanel(new GridBagLayout());
centerPanel.add(buttonPanel);
f.setContentPane(centerPanel);
f.pack(); // validates the layout and sets a size for the frame
f.setLocationRelativeTo(null); // centers the window on the screen
f.setExtendedState(JFrame.MAXIMIZED_BOTH); // maximizes the window
f.setVisible(true);
}
public static void main(String[] args) {
Runnable r = () -> new CenteredButtons();
SwingUtilities.invokeLater(r);
}
}

You need to subtract half the width and half the height of each of the buttons from the screen dimensions to center the two widgets.
Change the code where you set the bounds on the buttons to the following:
signup.setBounds(ss.width / 2 - 200 / 2, ss.height / 2 + 125 - 100 / 2, 200, 100);
login.setBounds(ss.width / 2 - 200 / 2, ss.height / 2 - 100 / 2, 200, 100);
To be notified when the user exits full screen mode, add a WindowStateListener to the frame and reset the bounds on the buttons.
Here's the complete code:
import javax.swing.*;
import java.awt.*;
import java.awt.event.WindowEvent;
import java.awt.event.WindowStateListener;
public class ChatWindow extends JFrame implements WindowStateListener{
Dimension ss;
JButton login;
JButton signup;
JFrame frame;
public ChatWindow() {
frame = new JFrame("EasyChat");
frame.addWindowStateListener(this);
login = new JButton("Login");
signup = new JButton("Don't have an account? Sign Up");
JPanel mainPanel = new JPanel();
ss = Toolkit.getDefaultToolkit().getScreenSize();
frame.setVisible(true);
frame.setLayout(null);
frame.setSize(800,450);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
frame.getContentPane().add(login);
frame.getContentPane().add(signup);
login.setPreferredSize(new Dimension(25,60));
login.setFont(new Font("HelveticaNeue", Font.BOLD, 20));
signup.setBounds(ss.width / 2 - 200 / 2, ss.height / 2 + 125 - 100 / 2, 200, 100);
login.setBounds(ss.width / 2 - 200 / 2, ss.height / 2 - 100 / 2, 200, 100);
mainPanel.setLayout(new BorderLayout());
mainPanel.setBorder(BorderFactory.createEmptyBorder(0, 10, 10, 10));
}
public static void main(String[] args) {
new ChatWindow();
}
#Override
public void windowStateChanged(WindowEvent e) {
Dimension ss = frame.getSize();
signup.setBounds(ss.width / 2 - 200 / 2, ss.height / 2 + 125 - 100 / 2, 200, 100);
login.setBounds(ss.width / 2 - 200 / 2, ss.height / 2 - 100 / 2, 200, 100);
}
}

JPanel Inside Of A JPanel

I am trying to get a JPanel to appear inside of another JPanel. Currently, the JPanel is in an external JFrame and loads with my other JFrame. I want the JPanel to be inside the other JPanel so the program does not open two different windows.
Here is a picture:
The small JPanel with the text logs I want inside of the main game frame. I've tried adding the panel to the panel, panel.add(othePanel). I've tried adding it the JFrame, frame.add(otherPanel). It just overwrites everything else and gives it a black background.
How can I add the panel, resize, and move it?
Edits:
That is where I want the chatbox to be.
Class code:
Left out top of class.
public static JPanel panel;
public static JTextArea textArea = new JTextArea(5, 30);
public static JTextField userInputField = new JTextField(30);
public static void write(String message) {
Chatbox.textArea.append("[Game]: " + message + "\n");
Chatbox.textArea.setCaretPosition(Chatbox.textArea.getDocument()
.getLength());
Chatbox.userInputField.setText("");
}
public Chatbox() {
panel = new JPanel();
panel.setPreferredSize(new Dimension(220, 40));
panel.setBackground(Color.BLACK);
JScrollPane scrollPane = new JScrollPane(textArea);
scrollPane.setPreferredSize(new Dimension(380, 100));
textArea.setLineWrap(true);
textArea.setWrapStyleWord(true);
textArea.setEditable(false);
scrollPane
.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
userInputField.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent event) {
String fromUser = userInputField.getText();
if (fromUser != null) {
textArea.append(Frame.username + ":" + fromUser + "\n");
textArea.setCaretPosition(textArea.getDocument()
.getLength());
userInputField.setText("");
}
}
});
panel.add(userInputField, SwingConstants.CENTER);
panel.add(scrollPane, SwingConstants.CENTER);
//JFrame frame = new JFrame();
//frame.add(panel);
//frame.setSize(400, 170);
//frame.setVisible(true);
}
Main frame class:
public Frame() {
frame.getContentPane().remove(loginPanel);
frame.repaint();
String capName = capitalizeString(Frame.username);
name = new JLabel(capName);
new EnemyHealth("enemyhealth10.png");
new Health("health10.png");
new LoadRedCharacter("goingdown.gif");
new Spellbook();
new LoadMobs();
new LoadItems();
new Background();
new Inventory();
new ChatboxInterface();
frame.setBackground(Color.black);
Frame.redHealthLabel.setFont(new Font("Serif", Font.PLAIN, 20));
ticks.setFont(new Font("Serif", Font.PLAIN, 20));
ticks.setForeground(Color.yellow);
Frame.redHealthLabel.setForeground(Color.black);
// Inventory slots
panel.add(slot1);
panel.add(name);
name.setFont(new Font("Serif", Font.PLAIN, 20));
name.setForeground(Color.white);
panel.add(enemyHealthLabel);
panel.add(redHealthLabel);
panel.add(fireSpellBookLabel);
panel.add(iceSpellBookLabel);
panel.add(spiderLabel);
panel.add(appleLabel);
panel.add(fireMagicLabel);
panel.add(swordLabel);
// Character
panel.add(redCharacterLabel);
// Interface
panel.add(inventoryLabel);
panel.add(chatboxLabel);
// Background
panel.add(backgroundLabel);
frame.setContentPane(panel);
frame.getContentPane().invalidate();
frame.getContentPane().validate();
frame.getContentPane().repaint();
//I WOULD LIKE THE LOADING OF THE PANEL SOMEWHERE IN THIS CONSTRUCTOR.
new ResetEntities();
frame.repaint();
panel.setLayout(null);
Run.loadKeyListener();
Player.px = Connect.x;
Player.py = Connect.y;
new Mouse();
TextualMenu.rect = new Rectangle(Frame.inventoryLabel.getX() + 80,
Frame.inventoryLabel.getY() + 100,
Frame.inventoryLabel.getWidth(),
Frame.inventoryLabel.getHeight());
Player.startMessage();
}

Don't use static variables.
Don't use a null layout.
Use appropriate layout managers. Maybe the main panel uses a BorderLayout. Then you add your main component to the CENTER and a second panel to the EAST. The second panel can also use a BorderLayout. You can then add the two components to the NORTH, CENTER or SOUTH as you require.

For example, using a custom Border:
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.Insets;
import java.awt.RadialGradientPaint;
import java.awt.geom.Point2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.*;
import javax.swing.border.AbstractBorder;
#SuppressWarnings("serial")
public class FrameEg extends JPanel {
public static final String FRAME_URL_PATH = "http://th02.deviantart.net/"
+ "fs70/PRE/i/2010/199/1/0/Just_Frames_5_by_ScrapBee.png";
public static final int INSET_GAP = 120;
private BufferedImage frameImg;
private BufferedImage smlFrameImg;
public FrameEg() {
try {
URL frameUrl = new URL(FRAME_URL_PATH);
frameImg = ImageIO.read(frameUrl);
final int smlFrameWidth = frameImg.getWidth() / 2;
final int smlFrameHeight = frameImg.getHeight() / 2;
smlFrameImg = new BufferedImage(smlFrameWidth, smlFrameHeight,
BufferedImage.TYPE_INT_ARGB);
Graphics g = smlFrameImg.getGraphics();
g.drawImage(frameImg, 0, 0, smlFrameWidth, smlFrameHeight, null);
g.dispose();
int top = INSET_GAP;
int left = top;
int bottom = top;
int right = left;
Insets insets = new Insets(top, left, bottom, right);
MyBorder myBorder = new MyBorder(frameImg, insets);
JTextArea textArea = new JTextArea(50, 60);
textArea.setWrapStyleWord(true);
textArea.setLineWrap(true);
for (int i = 0; i < 300; i++) {
textArea.append("Hello world! How is it going? ");
}
setLayout(new BorderLayout(1, 1));
setBackground(Color.black);
Dimension prefSize = new Dimension(frameImg.getWidth(),
frameImg.getHeight());
JPanel centerPanel = new MyPanel(prefSize);
centerPanel.setBorder(myBorder);
centerPanel.setLayout(new BorderLayout(1, 1));
centerPanel.add(new JScrollPane(textArea), BorderLayout.CENTER);
MyPanel rightUpperPanel = new MyPanel(new Dimension(smlFrameWidth,
smlFrameHeight));
MyPanel rightLowerPanel = new MyPanel(new Dimension(smlFrameWidth,
smlFrameHeight));
top = top / 2;
left = left / 2;
bottom = bottom / 2;
right = right / 2;
Insets smlInsets = new Insets(top, left, bottom, right);
rightUpperPanel.setBorder(new MyBorder(smlFrameImg, smlInsets));
rightUpperPanel.setLayout(new BorderLayout());
rightLowerPanel.setBorder(new MyBorder(smlFrameImg, smlInsets));
rightLowerPanel.setBackgroundImg(createBackgroundImg(rightLowerPanel
.getPreferredSize()));
JTextArea ruTextArea1 = new JTextArea(textArea.getDocument());
ruTextArea1.setWrapStyleWord(true);
ruTextArea1.setLineWrap(true);
rightUpperPanel.add(new JScrollPane(ruTextArea1), BorderLayout.CENTER);
JPanel rightPanel = new JPanel(new GridLayout(0, 1, 1, 1));
rightPanel.add(rightUpperPanel);
rightPanel.add(rightLowerPanel);
rightPanel.setOpaque(false);
add(centerPanel, BorderLayout.CENTER);
add(rightPanel, BorderLayout.EAST);
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
private BufferedImage createBackgroundImg(Dimension preferredSize) {
BufferedImage img = new BufferedImage(preferredSize.width,
preferredSize.height, BufferedImage.TYPE_INT_ARGB);
Point2D center = new Point2D.Float(img.getWidth()/2, img.getHeight()/2);
float radius = img.getWidth() / 2;
float[] dist = {0.0f, 1.0f};
Color centerColor = new Color(100, 100, 50);
Color outerColor = new Color(25, 25, 0);
Color[] colors = {centerColor , outerColor };
RadialGradientPaint paint = new RadialGradientPaint(center, radius, dist, colors);
Graphics2D g2 = img.createGraphics();
g2.setPaint(paint);
g2.fillRect(0, 0, img.getWidth(), img.getHeight());
g2.dispose();
return img;
}
private static void createAndShowGui() {
FrameEg mainPanel = new FrameEg();
JFrame frame = new JFrame("FrameEg");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.setResizable(false);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
#SuppressWarnings("serial")
class MyPanel extends JPanel {
private Dimension prefSize;
private BufferedImage backgroundImg;
public MyPanel(Dimension prefSize) {
this.prefSize = prefSize;
}
public void setBackgroundImg(BufferedImage background) {
this.backgroundImg = background;
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (backgroundImg != null) {
g.drawImage(backgroundImg, 0, 0, this);
}
}
#Override
public Dimension getPreferredSize() {
return prefSize;
}
}
#SuppressWarnings("serial")
class MyBorder extends AbstractBorder {
private BufferedImage borderImg;
private Insets insets;
public MyBorder(BufferedImage borderImg, Insets insets) {
this.borderImg = borderImg;
this.insets = insets;
}
#Override
public void paintBorder(Component c, Graphics g, int x, int y, int width,
int height) {
g.drawImage(borderImg, 0, 0, c);
}
#Override
public Insets getBorderInsets(Component c) {
return insets;
}
}
Which would look like:

EmptyBorders on JPanel in BoxLayout.X_AXIS

I have a custom JPanel, which the paintComponent method is overridden to paint an image.
I want to insert several of these custom panels vertically centered in a container. To do this I created a jpanel with BoxLayout.X_AXIS as layout manager.
This works great and shows what I want, but I would like to add margins between the custom panels.
The EmptyMargins are just ignored, and the tricky part is that I can't (or would not like to...) add struts or boxes between them because I need to get each custom panel from a loop which takes all components of the container and cast them into CustomPanel.
See the problem ? If I add struts between the panels there will be a cast exception and EmptyBorders aren't working... Any ideas welcome!
Note : I'm open to other layout manager propositions ! ;-)
Here is the code :
public class StackExemple {
public StackExemple() {
JFrame frame = new JFrame();
frame.setPreferredSize(new Dimension(600, 300));
JPanel container = new JPanel();
container.setPreferredSize(new Dimension(600, 300));
container.setLayout(new BoxLayout(container, BoxLayout.X_AXIS));
CustomPanel customPanel1 = new CustomPanel();
CustomPanel customPanel2 = new CustomPanel();
CustomPanel customPanel3 = new CustomPanel();
container.add(customPanel1);
container.add(customPanel2);
container.add(customPanel3);
frame.getContentPane().add(container);
frame.pack();
frame.setVisible(true);
//Loop which takes the custompanels
for(Component comp : container.getComponents()) {
CustomPanel panel = (CustomPanel)comp;
//DO SOMETHING
System.out.println("Hello World");
}
}
private class CustomPanel extends JPanel{
private BufferedImage image;
public CustomPanel() {
setPreferredSize(new Dimension(100, 100));
setMinimumSize(getPreferredSize());
setMaximumSize(getPreferredSize());
setBorder(BorderFactory.createEmptyBorder(0,50,0,0));
setBackground(Color.RED);
// try {
// image = ImageIO.read(ClassLoader.getSystemClassLoader().getResource("Ressources/img.png"));
// } catch (IOException ex) {
// System.out.println("Ooops... ");
// }
}
#Override
protected void paintComponent(Graphics g)
{
super.paintComponent(g);
// int x = (this.getWidth() - image.getWidth()) / 2;
// int y = (this.getHeight() - image.getHeight()) / 2;
// g.drawImage(image, x, y, null);
}
}
}

Borders are correct, have to getBackground from parent for LineBorders
override Min / Max / PreferredSize for BoxLayout
BoxLayout accepting Min / Max / PreferredSize by default
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.image.BufferedImage;
import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class StackExemple {
public StackExemple() {
JFrame frame = new JFrame();
JPanel container = new JPanel();
container.setLayout(new BoxLayout(container, BoxLayout.X_AXIS));
CustomPanel customPanel1 = new CustomPanel(Color.blue);
CustomPanel customPanel2 = new CustomPanel(Color.red);
CustomPanel customPanel3 = new CustomPanel(Color.green);
container.add(customPanel1);
container.add(customPanel2);
container.add(customPanel3);
frame.getContentPane().add(container);
frame.pack();
frame.setVisible(true);
for (Component comp : container.getComponents()) {
CustomPanel panel = (CustomPanel) comp;
System.out.println("Hello World");
}
}
private class CustomPanel extends JPanel {
private BufferedImage image;
#Override
public Dimension getMinimumSize() {
return new Dimension(100, 80);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(200, 160);
}
#Override
public Dimension getMaximumSize() {
return new Dimension(400, 320);
}
public CustomPanel(Color c) {
setBorder(BorderFactory.createCompoundBorder(
BorderFactory.createEmptyBorder(10, 10, 10, 10),
BorderFactory.createLineBorder(Color.black, 1)));
//setBorder(BorderFactory.createCompoundBorder(
//BorderFactory.createLineBorder(Color.black, 1),
//BorderFactory.createEmptyBorder(10, 10, 10, 10)));
setBackground(c);
}
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
StackExemple stackExemple = new StackExemple();
}
});
}
}

The underlying reason that the border appears to not be respected is that the panel by default is opaque, that is it guarantees to fill each pixel of its area with a fully solid background color. The area covered by the border is part of the panel's area, so must be filled with the panel's background as well.
As you seem to be doing custom painting anyway, you might consider to report its opaqueness as false and only paint the background (and/or the background image) inside the bordered area:
// in constructor
setOpaque(false);
#Override
protected void paintComponent(Graphics g) {
// take over background filling inside the border
Insets insets = getInsets();
g.setColor(getBackground());
g.fillRect(insets.left, insets.top,
getWidth() - insets.left - insets.right,
getHeight() - insets.top - insets.bottom);
super.paintComponent(g);
// for a background image, you would need to take the insets
// into account as well
// int x = (this.getWidth() - image.getWidth()) / 2;
// int y = (this.getHeight() - image.getHeight()) / 2;
// g.drawImage(image, x, y, null);
}

How to change the dimension of a component in a JFrame

Suppose I have a JPanel in a JFrame. When I invoke a method that changes the preferred size of that JPanel, it does not change.
The code looks something like this:
public class SomePanel extends JPanel{
public SomePanel(){
setPreferredSize( new Dimension( 390, 40 ) );
setBackground( Color.BLACK );
}
public void expand(){
setPreferredSize( new Dimension( 390, 200 ) );
}
public static void main( String args[] ){
JFrame frame = new JFrame();
frame.setSize( 450, 500 );
frame.setLayout( new FlowLayout() );
SomePanel somePanel = new SomePanel();
frame.add( somePanel );
frame.setVisible( true );
somePanel.expand();
}
}
Is there something that I have to do first? I have tried so check the size of the JPanel when expand() is invoked. The height of the JPanel before and after setting the preferred size remains at 40.
I have also tried to use a Dimension variable, and that did not work either.
Dimension dimension;
public SomePanel(){
dimension = new Dimension( 390, 40 );
...
}
public expand(){
dimension.setSize( 390, 200 );
setPreferredSize( dimension );
}

Add frame.pack(); after somePanel.expand(); in your main() method. It will be done.

You need to invalidate the container hierarchy to make it re-layout the components.
Simply call invalidate followed by revalidate on the component you have changed.
Here's a small example...
public class TestComponentHierarcy {
public static void main(String[] args) {
new TestComponentHierarcy();
}
public TestComponentHierarcy() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException ex) {
} catch (InstantiationException ex) {
} catch (IllegalAccessException ex) {
} catch (UnsupportedLookAndFeelException ex) {
}
JFrame frame = new JFrame("Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new GridBagLayout());
frame.add(new Test());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class Test extends JPanel {
private Dimension size = new Dimension(10, 10);
public Test() {
setLayout(new GridBagLayout());
addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
size.width += 10;
size.height += 10;
invalidate();
revalidate();
}
});
}
#Override
public Dimension getPreferredSize() {
return size;
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.RED);
g.drawRect(0, 0, getWidth() - 1, getHeight() - 1);
}
}
}

+1 to all.
I usually use a combination of:
revalidate() and pack(). (see #GagandeepBali and #StanislavL answer here for more reasoning as to my choice of revalidate()) as for pack() this allows for my JFrame to be sized to fit the contents.
do not call setPreferredSize rather override getPreferredSize of JPanel.
also do not call setSize(..) on JFrame use correct LayoutManager which adjusts to all added components size and than simply call pack() before setting JFrame visible.
And lastly but not stressed enough warp creation and manipulation of Swing components in SwingUtilities.invokeXXX block / Event Dispatch Thread
Here is an example I made:
Basically a JPanel which overrides getPreferredSize and has a method setPanelSize(int w,int h) which changes variables in JPanel instance to return new Dimensions for getPreferredSize. after that I call revalidate() and pack() on JFrame to refelect changes:
import java.awt.BorderLayout;
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;
import javax.swing.SwingUtilities;
public class Test {
public Test() {
initComponents();
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new Test();
}
});
}
private void initComponents() {
final JFrame frame = new JFrame();
frame.setTitle("Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
final MyPanel myPanel = new MyPanel();
final JButton changeSizeButton = new JButton("Change size to 300x300");
changeSizeButton.addActionListener(new ActionListener() {
boolean resized = false;
#Override
public void actionPerformed(ActionEvent ae) {
if (resized) {
myPanel.setPanelSize(200, 200);
resized = false;
changeSizeButton.setText("Change size to 300x300");
} else {
myPanel.setPanelSize(300, 300);
resized = true;
changeSizeButton.setText("Change size to 200x200");
}
frame.revalidate();
frame.pack();
}
});
frame.add(myPanel);
frame.add(changeSizeButton, BorderLayout.SOUTH);
frame.pack();
frame.setVisible(true);
}
}
class MyPanel extends JPanel {
private int width, height;
public MyPanel() {
super(true);
width = 200;
height = 200;
}
#Override
public Dimension getPreferredSize() {
return new Dimension(width, height);
}
public void setPanelSize(int width, int height) {
this.width = width;
this.height = height;
}
}