Develop Reference

Java&Swing: why the componenet isn't added dynamically?

The following is my code.
I think click the button, at least, a Color.CYAN block will be added into MainPanel, but it doesn't.
Could you please tell me how to achieve that? Thanks.
public class TestFrame extends JFrame {
public static void main(String[] args) {
EventQueue.invokeLater(() -> {
final TestFrame mainFrame = new TestFrame();
mainFrame.setDefaultCloseOperation(EXIT_ON_CLOSE);
mainFrame.setVisible(true);
});
}
public TestFrame() throws HeadlessException {
setTitle("Frame");
setSize(new Dimension(1000, 800));
final JPanel mainPanel = new JPanel();
final JButton button = new JButton("Test");
button.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
System.out.println(e.getActionCommand());
mainPanel.add(new Unit());
}
});
mainPanel.add(button);
mainPanel.revalidate();
add(mainPanel);
}
class Unit extends JComponent {
public Unit() {
setSize(new Dimension(100, 100));
setBackground(Color.CYAN);
}
#Override
protected void paintComponent(Graphics g) {
final Graphics2D g2D = (Graphics2D) g;
g2D.drawString("Hello World", 10, 10);
}
}
}

Your Unit JComponent is likely being added to mainPanel in the ActionListener and thus the GUI, but it has no preferred size and so per the FlowLayout used by JPanels, it will size to [0, 0]. FlowLayouts (and most layout managers) do not respect a component's size but rather its preferredSize. Also, revalidate() and repaint() need to be called on the container (mainPanel) after Unit has been added so that the layout managers can do their laying out of components and to allow the OS to clear dirty pixels.
To solve this, give it a preferred size, preferably by overriding public Dimension getPreferredSize() but by calling setPreferredSize(...) if you must, and by calling revalidate() and repaint() after adding the component to the container.
Better still, add the component to the container using a CardLayout tutorial, but hide it by also adding an empty JLabel, again using a CardLayout, and then display the hidden component by calling CardLayout.show(...) from within ActionListener.
Side note: don't forget the super method within your painting method:
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g); // add this ****
final Graphics2D g2D = (Graphics2D) g;
g2D.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING, RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
g2D.setFont(UNIT_FONT);
g2D.drawString("Hello World", textX, textY);
}
else you break the painting chain and may see unwanted artifacts or other problems
e.g.,
import java.awt.*;
import javax.swing.*;
#SuppressWarnings("serial")
public class TestFrame extends JFrame {
private CardLayout cardLayout = new CardLayout();
private JPanel cardPanel = new JPanel(cardLayout);
public static void main(String[] args) {
EventQueue.invokeLater(() -> {
final TestFrame mainFrame = new TestFrame();
mainFrame.setDefaultCloseOperation(EXIT_ON_CLOSE);
mainFrame.pack();
mainFrame.setLocationRelativeTo(null);
mainFrame.setVisible(true);
});
}
public TestFrame() throws HeadlessException {
setTitle("Frame");
setPreferredSize(new Dimension(1000, 800));
final JPanel mainPanel = new JPanel(new BorderLayout());
final JButton button = new JButton("Test");
button.addActionListener(e -> {
cardLayout.next(cardPanel);
});
JPanel btnPanel = new JPanel();
btnPanel.add(button);
mainPanel.add(btnPanel, BorderLayout.PAGE_END);
mainPanel.add(cardPanel);
add(mainPanel);
cardPanel.add(new JLabel(), "Foo");
cardPanel.add(new Unit(), Unit.class.getCanonicalName());
}
static class Unit extends JPanel {
private static final int PREF_W = 100;
private static final int PREF_H = 100;
private static final Font UNIT_FONT = new Font(Font.SANS_SERIF, Font.BOLD, 60);
public Unit() {
setBackground(Color.CYAN);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
final Graphics2D g2D = (Graphics2D) g;
g2D.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING, RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
g2D.setFont(UNIT_FONT);
g2D.drawString("Hello World", 360, 350);
}
}
}

How do I change what's being displayed in Java Swing?

I don't really know how to word this question, but I can explain what I'm trying to do.
I have my program drawing a basic menu with a background image and 3 buttons along the bottom. I want to make it so that when I press one of the buttons, the menu and the background image change to a different scene. Like pressing play to start a game or pressing options to go to an option menu.
This is my code for the primary menu:
private final void initUI() {
JPanel panel = new JPanel();
panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
add(panel);
panel.add(Box.createVerticalGlue());
JPanel bottom = new JPanel();
bottom.setAlignmentX(1f);
bottom.setLayout(new BoxLayout(bottom, BoxLayout.X_AXIS));
JButton plyBtn = new JButton("Play");
plyBtn.addActionListener(new ActionListener(){
#Override
public void actionPerformed(ActionEvent event){
GameFrame_Test1 game1 = new GameFrame_Test1();
game1.setVisible(true);
}
});
JButton opBtn = new JButton("Options");
JButton quitButton = new JButton("Exit");
quitButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent event) {
System.exit(0);
}
});
bottom.add(plyBtn);
bottom.add(Box.createRigidArea(new Dimension(100, 0)));
bottom.add(opBtn);
bottom.add(Box.createRigidArea(new Dimension(100, 0)));
bottom.add(quitButton);
bottom.add(Box.createRigidArea(new Dimension(100, 0)));
panel.add(new GraphicTest_1());
panel.add(bottom);
panel.add(Box.createRigidArea(new Dimension(0,15)));
setTitle("Justice GUI");
setSize(1280, 720);
setLocationRelativeTo(null);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
DisplayFrame ex = new DisplayFrame();
ex.setVisible(true);
}
});
}
This is my code for the frame I want to change to so far:
class GameFrame_Test1 extends JPanel{
private Image mshi;
public GameFrame_Test1() {
loadImage();
setSurfaceSize();
}
private void loadImage() {
mshi = new ImageIcon("content/Placeholder_Map.png").getImage();
}
private void setSurfaceSize() {
Dimension d = new Dimension();
d.width = mshi.getWidth(null);
d.height = mshi.getHeight(null);
setPreferredSize(d);
}
private void doDrawing(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
g2d.drawImage(mshi, 0, 0, null);
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
doDrawing(g);
}
}
I am very new to Java Swing, and this is a test program for me to learn how to use it. I have looked online for a solution, but not being able to word my question makes it hard. Thanks to anyone who can help!

I want to make it so that when I press one of the buttons, the menu and the background image change to a different scene.
You should be using a Card Layout as the layout manager of the content panel. Then you can swap a different panel on the frame when a button is clicked.
Check out the section from the Swing tutorial on How to Use CardLayout for more information and working examples.

KeyEvent won't change background color of JPanels

I want the KeyEvent to change the background color of my JPanels. Nothing happens when I press anything on the keyboard. One of my applications specifications is that I need a 'Customized component extended from JPanel.' which is why I have another class for my graphics panel.
My problem is when G is pressed nothing happens but my center panel should turn green...
Here is code for part of my application.
public class Maths extends JFrame implements KeyListener
{
private JPanel pNorth = new JPanel();
private JPanel pSouth = new JPanel();
private JPanel pCenter = new JPanel();
private JPanel pEast = new JPanel();
private JPanel pWest = new JPanel();
private File file;
private JPanel pDraw = new GraphicsPanel();
public static void main(String args[])
{
new Maths();
}
public Maths()
{
mainFrame = new JFrame();
mainFrame.setTitle("Maths Test Game");
mainFrame.setLayout(new BorderLayout());
mainFrame.setSize(1200, 800);
mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
mainFrame.add(pNorth, BorderLayout.NORTH);
mainFrame.add(pSouth, BorderLayout.SOUTH);
mainFrame.add(pCenter, BorderLayout.CENTER);
mainFrame.add(pEast, BorderLayout.EAST);
mainFrame.add(pWest, BorderLayout.WEST);
pNorth.setLayout(new FlowLayout());
pSouth.setLayout(new FlowLayout());
pCenter.setLayout(new FlowLayout());
pEast.setLayout(new FlowLayout());
pWest.setLayout(new FlowLayout());
addKeyListener(this);
setFocusable(true);
mainFrame.setVisible(true);
}
class GraphicsPanel extends JPanel
{
GraphicsPanel()
{
// set a preferred size for the custom panel.
setPreferredSize(new Dimension(250, 300));
}
#Override
public void paint(Graphics g)
{
super.paint(g);
// set blue color for drawing
g.setColor(Color.blue);
// face
g.drawOval(90, 70, 80, 80);
// eyes
g.drawOval(110, 95, 5, 5);
g.drawOval(145, 95, 5, 5);
// nose
g.drawLine(130, 95, 130, 115);
// mouth
g.drawArc(113, 115, 35, 20, 0, -180);
}
}
#Override
public void keyPressed(KeyEvent e)
{
if(e.getKeyCode() == KeyEvent.VK_G)
{
pCenter.setBackground(Color.green);
}
repaint();
}
#Override
public void keyReleased(KeyEvent e)
{
}
#Override
public void keyTyped(KeyEvent e)
{
}
}

There are a multitude of reasons this is probably not working, generally, you don't want to attach KeyListeners to top level containers like JFrame, as they is simply to many things that can get in the way and prevent the frame from raising key events.
Instead, use the key bindings API. See How to Use Key Bindings for more details

JPanel won't move if it fills the screen

First of all, sorry for the vague title I don't know how to word the question in a sentence.
I have a simple programme that slides one JPanel into view as another gets pushed out, when a button is clicked.
If the first JPanel's width is set as getWidth() then the JPanel will not move when the button is clicked, however if I change the width to getWidth() - 1 it works perfectly fine!?!
A simple example is shown below
public class SlidingJPanel extends JFrame{
public JPanel panel = new JPanel();
public JPanel panel2 = new JPanel();
public JLabel label = new JLabel(" SUCCESS!!!!!!!");
public JButton button = new JButton("TESTING");
public class MyJPanel extends JPanel implements ActionListener{
public int x = 0;
public int delay = 70;
final Timer timer = new Timer(delay,this);
public MyJPanel(){};
public void paintComponent(Graphics g)
{
super.paintComponent(g);
button.setBounds(10, 20, 100, 50);
button.addActionListener(this);
panel.setBorder(BorderFactory.createLineBorder(Color.black));
panel.setBounds(x, 0, getWidth(), getHeight());
panel.add(button);
panel2.setBorder(BorderFactory.createLineBorder(Color.blue));
panel2.setBounds(x - getWidth(), 0, getWidth(), getHeight());
panel2.add(label);
add(panel);
add(panel2);
}
#Override
public void actionPerformed(ActionEvent arg0) {
timer.addActionListener(move);
timer.start();
}
ActionListener move = new ActionListener(){
public void actionPerformed(ActionEvent e){
repaint();
x++;
}
};
}
public static void main(String args [])
{
new SlidingJPanel();
}
SlidingJPanel()
{
Container container = getContentPane();
MyJPanel panel = new MyJPanel();
container.add(panel);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setSize(500,500);
setTitle("JPanel Draw Rect Animation");
setVisible(true);
}
}
ignore any coding conventions I may have ignored or missed this is just a rough draft.
Hope someone can help :)

The paintComponent() method is for painting only! There is no need for you to override this method.
You should NOT be:
updating the property of components (ie. bounds, border)
adding components to a container
If you want to animate a component then when the timer fires you can use setLocation(...) or setSize() or setBounds(). The component will automatically be repainted.
I don't know if fixing this will solve your problem, but the current approach is wrong.

Transparent JPanel

I want to create a semi-transparent JPanel. I've done it by simply using RGBA value of color constructor but problem is when i m using event handling is not woking properly. My requirement is a semi transparent Jpanel when mouse enters it border of this panel became visible and if mouse exit the border shoud not visible. I have done this by following code but problem is its not working properly for transparent backgroud (RGBA) but it working fine for RGB color.
import javax.swing.*;
import javax.swing.border.*;
import java.awt.*;
import java.awt.event.*;
public class MDCW extends JFrame {
private JPanel contentPane;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
MDCW frame = new MDCW();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public MDCW() {
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 1013, 551);
contentPane = new JPanel();
contentPane.setBackground(new Color(0, 139, 139));
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
final JPanel panel = new JPanel();
panel.setBackground(new Color(0, 0, 0,50));
panel.addMouseListener(new MouseAdapter() {
#Override
public void mouseEntered(MouseEvent e) {
panel.setBorder(new LineBorder(new Color(255, 255, 255), 5));
}
#Override
public void mouseExited(MouseEvent e) {
panel.setBorder(null);
}
});
panel.setBounds(360, 155, 215, 215);
contentPane.add(panel);
final JPanel panel_1 = new JPanel();
panel_1.setBackground(new Color(0, 0, 0));
panel_1.addMouseListener(new MouseAdapter() {
#Override
public void mouseEntered(MouseEvent e) {
panel_1.setBorder(new LineBorder(new Color(255, 255, 255), 5));
}
#Override
public void mouseExited(MouseEvent e) {
panel_1.setBorder(null);
}
});
panel_1.setBounds(84, 155, 215, 215);
contentPane.add(panel_1);
}
}

JPanel does not support semi-transparent backgrounds. There are two steps needed to take care of this problem:
First, to have any correctly-functioning transparency at all, you must setOpaque(false) on the panel; otherwise you will have glitches, because an opaque panel is assumed to completely cover what is underneath its bounds.
However, when opaque is false, the panel also does not draw its background at all (!) so you will have to draw a background in paintComponent.
Here is a drop-in replacement class which will take care of both of these steps.
private class TransparentPanel extends JPanel {
{
setOpaque(false);
}
public void paintComponent(Graphics g) {
g.setColor(getBackground());
Rectangle r = g.getClipBounds();
g.fillRect(r.x, r.y, r.width, r.height);
super.paintComponent(g);
}
}
I’ve checked that it works in your program if I change the first panel creation to:
final JPanel panel = new TransparentPanel();

It's easy to do it like so:
// initialise JPanel
JPanel somePanel = new JPanel(new GridBagLayout());
somePanel.setBackground(new Color(0,0,0,x);
x in this case is the level of transparency you're looking for
0 being invisible, 100 being solid.
e.g:
somePanel.setBackground(new Color(0,0,0,55)
See:
http://docs.oracle.com/javase/7/docs/api/java/awt/Color.html
http://docs.oracle.com/javase/7/docs/api/javax/swing/JComponent.html