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JScrollPane override setHvalue

I would like to modify my JScrollPane so that when the horizontal position is changed, the position hvalue is sent to another class. I don't want the other class to have to retrieve this value every time as this will happen repeatedly during a task which must be finished as quickly as possible.
I haven't been able to find any documentation on the exact syntax used by default but I'm guessing what I want will look something like this:
import java.lang.Math.*;
import javax.swing.*;
public class scroll {
public static void main(String[] args) {
JFrame f = new JFrame();
f.setDefaultCloseOperation(3);
panel p = new panel();
JScrollPane sp = new JScrollPane(p,21,31) {
#Override
public final void setHvalue(double value) {
hvalue = value;
p.sendH((int) Math.round(value));
}
};
f.add(sp);
f.setSize(333,333);
f.setVisible(true);
}
}
which will include a panel object governed by the class:
import javax.swing.*;
public class panel extends JPanel {
private static int H;
public panel() {}
public static void sendH(int x) {
H=x;
System.out.println(x);
}
}
Attempting to compile this code yields the error messages:
scroll.java.11: error: method does not override or implement a method from supertype
#Override
scroll.java.13: error: cannot find symbol
hvalue = value;
symbol: variable hvalue
which, as I understand it, is basically their way of saying I can't modify setHvalue(). Is there some way around this or an alternative way of sending hvalue when it's changed instead of retrieving it every time it's needed?

when the horizontal position is changed, the position hvalue is sent to another class.
This is done by adding an AdjustmentListener to the horizontal scrollbar.
However, this is extra overhead that is NOT required if you do not use the information every time it changes.
I do not recommend using this approach.
I don't want the other class to have to retrieve this value every time as this will happen repeatedly during a task which must be finished as quickly as possible.
Invoking the getValue() method of the scrollbar will NOT add any measurable overhead to your task.
Your task just needs a reference to the scroll pane so you can access the scrollbar and get the current value.

Actually I figured out the answer, sorry about that. It turns out that the method getHvalue is only for awt ScrollPane and is not inherited by swing JScrollPane. I will post a working version here, in case someone else is interested some day (although I'm guessing that camickr's approach is better).
The JScrollPane class is:
import java.awt.*;
import javax.swing.*;
import javax.accessibility.*;
public class scroll {
public static void main(String[] args) {
JFrame f = new JFrame();
f.setDefaultCloseOperation(3);
panel p = new panel() {
#Override
public Dimension getMinimumSize(){
return new Dimension(getWidth(),getHeight());
}
#Override
public Dimension getPreferredSize(){
return new Dimension(getWidth(),getHeight());
}
#Override
public Dimension getMaximumSize(){
return new Dimension(getWidth(),getHeight());
}
};
JScrollPane sp = new JScrollPane(p,22,32);
sp.setHorizontalScrollBar( new JScrollBar(JScrollBar.HORIZONTAL){
#Override
public void setValue(int value) {
BoundedRangeModel m = getModel();
int oldValue = m.getValue();
m.setValue(value);
if (accessibleContext != null) {
accessibleContext.firePropertyChange(
AccessibleContext.ACCESSIBLE_VALUE_PROPERTY,
Integer.valueOf(oldValue),
Integer.valueOf(m.getValue()));
}
p.sendH(value);
}
});
f.add(sp);
f.setSize(333,333);
p.setSize(400,400);
f.setVisible(true);
}
}
and the panel class is:
import javax.swing.*;
public class panel extends JPanel {
private static int H;
public panel() {}
public static void sendH(int x) {
H=x;
System.out.println(x);
}
}

more efficiently load images for JList, presumably with SwingWorker

I have a problem in which I hope SwingWorker can help me, but I am not quite sure how to integrate it in my program.
The problem:
In a CardLayout I have a button on Card1 that opens Card2.
Card2 has a JList with a custom renderer(extending JLabel) which will display on average 1 to 6 images which are:
PNGs
around 500kb in size
loaded via imageIO with the change of cards
the renderer applies heavy operations such as image scaling or blurring and than sets the image as JLabel icon.
This can almost take up to a second if around 6 images have to be rendered, which is does not happen frequently but even that occasional split second of unresponsiveness feels bad.
Now I thought a SwingWorker might help here, but I'm thoroughly confused as to how I would have to integrate it.
Assuming we had this Code snippet
import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
public class Example {
private JPanel mainPanel = new JPanel();
private JList<Product> list = new JList();
private JScrollPane scroll = new JScrollPane();
private Map<String, Color> colorMap = new HashMap<>();
public Example() {
colorMap.put("red", Color.red);
colorMap.put("blue", Color.blue);
colorMap.put("cyan", Color.cyan);
colorMap.put("green", Color.green);
colorMap.put("yellow", Color.yellow);
mainPanel.setBackground(new Color(129, 133, 142));
scroll.setViewportView(list);
scroll.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
scroll.setPreferredSize(new Dimension(80,200));
list.setCellRenderer(new CustomRenderer());
DefaultListModel model = new DefaultListModel();
model.addElement(new Product("red"));
model.addElement(new Product("yellow"));
model.addElement(new Product("blue"));
model.addElement(new Product("red"));
model.addElement(new Product("cyan"));
list.setModel(model);
mainPanel.add(scroll);
}
public static void main(String[] args) throws IOException {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new JFrame("WorkerTest");
frame.setContentPane(new Example().mainPanel);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocation(300, 300);
frame.setMinimumSize(new Dimension(160, 255));
frame.setVisible(true);
}
});
}
class CustomRenderer extends JLabel implements ListCellRenderer<Product> {
private Product product;
public CustomRenderer() {
setOpaque(false);
}
#Override
public Component getListCellRendererComponent(JList<? extends Product> list, Product product, int index, boolean isSelected, boolean cellHasFocus) {
this.product = product;
/**
* in the actual code image is png with alpha channel respectively named to the productID of the JList object
*
* String id = product.getId();
* image = ImageIO.read(getClass().getResource("../../resources/images/" + id + ".png"));
*/
BufferedImage image1 = new BufferedImage(80, 50, BufferedImage.TYPE_INT_RGB);
BufferedImage image2 = new BufferedImage( 80, 75, BufferedImage.TYPE_INT_RGB);
Graphics g = image2.getGraphics();
/**
* this is only an example, in the actual code I might also apply gaussian blurs or rescale several time
*/
g.drawImage(image1,0,0,null);
setIcon(new ImageIcon(image2));
return this;
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(colorMap.get(product.getColor()));
g.fillRect(0,0,80,75);
}
}
class Product {
String productID;
String color;
public Product(String color) {
this.color = color;
}
public String getColor() {
return color;
}
public String getProductID() {
return productID;
}
}
}
would I have to call a SwingWorker from every getListCellRendererComponent call
to take over the image operations ?
Is SwingWorker even the right tool for this problem?
any help as to how I can make this part of my GUI faster would be greatly appreciated.
EDIT:
Hovercraft Full Of Eels mentioned that preloading the images could help and that loading the images from the renderer is fundamentally wrong.
This leads me to another Question:
I have a list(let's call it list1) with around 3000 objects each object has a 8kb jpg thumbnail which is load via object ID (also during the rendering)
The list displays around 6 to 12 of these thumbnail at the same time (due to the List's Dimension)
when the user selects an object he can press a button to display Card2 from the Cardlayout mentioned in the original question and it's list(list2) with the Object
and all it's related Object in non thumbnail view (500kb png + heavy image operation). Now I think it would be feasible to preload the non thumbnail image of the Object and it's relations selected in the first list which would be around 1-6 images. If I understood correctly what Hovercraft Full Of Eels said, then I could use a SwingWorker to load these Images after the selection of an Object from list1.
But what about the around 3000 images from list1, the program seemingly is not slowed down or becomes unresponsive because they are rather small in size and there are no heavy operations on the thumbnails, but they are still load form the list1's renderer. Would it make sense to preload the several thousand thumbnails ?
btw. feel free to tell me if this kind of question edit is not wished for and if it should be made into a question of itself.

One approach might be the following:
Whenever a cell renderer component for a certain element (Product) is requested, you check whether the matching image is already loaded. If not, you start a Swing worker that does the work of loading and processing the image in the background. When the worker is done, the image is placed into a cache for later lookup. In the meantime, you let the renderer just say "Loading..." or something.
A very quick implementation is here:
And as an MCVE:
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Collections;
import java.util.Map;
import java.util.Objects;
import java.util.Random;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Function;
import javax.swing.DefaultListModel;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.ListCellRenderer;
import javax.swing.SwingWorker;
public class LazyImageLoadingCellRendererTest
{
private JPanel mainPanel = new JPanel();
private JList<Product> list = new JList<Product>();
private JScrollPane scroll = new JScrollPane();
public LazyImageLoadingCellRendererTest()
{
mainPanel.setBackground(new Color(129, 133, 142));
scroll.setViewportView(list);
scroll.setHorizontalScrollBarPolicy(
JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
scroll.setPreferredSize(new Dimension(80, 200));
list.setCellRenderer(new LazyImageLoadingCellRenderer<Product>(list,
LazyImageLoadingCellRendererTest::loadAndProcessImage));
DefaultListModel<Product> model = new DefaultListModel<Product>();
for (int i=0; i<1000; i++)
{
model.addElement(new Product("id" + i));
}
list.setModel(model);
mainPanel.add(scroll);
}
public static void main(String[] args) throws IOException
{
EventQueue.invokeLater(new Runnable()
{
#Override
public void run()
{
JFrame frame = new JFrame("WorkerTest");
frame.setContentPane(
new LazyImageLoadingCellRendererTest().mainPanel);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocation(300, 300);
frame.setMinimumSize(new Dimension(160, 255));
frame.setVisible(true);
}
});
}
private static final Random random = new Random(0);
private static BufferedImage loadAndProcessImage(Product product)
{
String id = product.getProductID();
int w = 100;
int h = 20;
BufferedImage image =
new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
Graphics2D g = image.createGraphics();
g.setColor(Color.GREEN);
g.fillRect(0, 0, w, h);
g.setColor(Color.BLACK);
g.drawString(id, 10, 16);
g.dispose();
long delay = 500 + random.nextInt(3000);
try
{
System.out.println("Load time of " + delay + " ms for " + id);
Thread.sleep(delay);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
return image;
}
class Product
{
String productID;
public Product(String productID)
{
this.productID = productID;
}
public String getProductID()
{
return productID;
}
}
}
class LazyImageLoadingCellRenderer<T> extends JLabel
implements ListCellRenderer<T>
{
private final JList<?> owner;
private final Function<? super T, ? extends BufferedImage> imageLookup;
private final Set<T> pendingImages;
private final Map<T, BufferedImage> loadedImages;
public LazyImageLoadingCellRenderer(JList<?> owner,
Function<? super T, ? extends BufferedImage> imageLookup)
{
this.owner = Objects.requireNonNull(
owner, "The owner may not be null");
this.imageLookup = Objects.requireNonNull(imageLookup,
"The imageLookup may not be null");
this.loadedImages = new ConcurrentHashMap<T, BufferedImage>();
this.pendingImages =
Collections.newSetFromMap(new ConcurrentHashMap<T, Boolean>());
setOpaque(false);
}
class ImageLoadingWorker extends SwingWorker<BufferedImage, Void>
{
private final T element;
ImageLoadingWorker(T element)
{
this.element = element;
pendingImages.add(element);
}
#Override
protected BufferedImage doInBackground() throws Exception
{
try
{
BufferedImage image = imageLookup.apply(element);
loadedImages.put(element, image);
pendingImages.remove(element);
return image;
}
catch (Exception e)
{
e.printStackTrace();
return null;
}
}
#Override
protected void done()
{
owner.repaint();
}
}
#Override
public Component getListCellRendererComponent(JList<? extends T> list,
T value, int index, boolean isSelected, boolean cellHasFocus)
{
BufferedImage image = loadedImages.get(value);
if (image == null)
{
if (!pendingImages.contains(value))
{
//System.out.println("Execute for " + value);
ImageLoadingWorker worker = new ImageLoadingWorker(value);
worker.execute();
}
setText("Loading...");
setIcon(null);
}
else
{
setText(null);
setIcon(new ImageIcon(image));
}
return this;
}
}
Note:
This is really just a quick example showing the general approach. Of course, this could be improved in many ways. Although the actual loading process is already pulled out into a Function (thus making it generically applicable for any sort of image, regardless of where it comes from), one major caveat is that: It will try to load all images. A nice extension would be to add some smartness here, and make sure that it only loads the images for which the cells are currently visible. For example, when you have a list of 1000 elements, and want to see the last 10 elements, then you should not have to wait for 990 elements to be loaded. The last elements should be priorized higher and loaded first. However, for this, a slightly larger infrastructure (mainly: an own task queue and some stronger connection to the list and its scroll pane) may be necessary. (I'll possibly tackle this one day, because it might be a nice and interesting thing to have, but until then, the example above might do it...)

would I have to call a SwingWorker from every getListCellRendererComponent call to take over the image operations ?
No, you would in fact never call a background thread from within a key rendering method. In fact this appears to be the main problem with the code above -- you're reading in images from within a rendering method, significantly reducing the perceived responsiveness of your program.
Is SwingWorker even the right tool for this problem?
Perhaps, but not where you're thinking about using it. A SwingWorker will not speed anything up, but by performing long-running tasks in the background, it would avoid blocking the Swing event thread, freezing the GUI. Best would be to read the images, once, perhaps in a SwingWorker if not done during program initiation, and save them to a variable. Do not re-read the image every time you want to render it, if this can be avoided. And again, do not read in the image from within your rendering code as this will significantly reduce the perceived responsiveness of the program.

Hint for JTextField / JPasswordField

I built a class extending the JTextField class and an own hint function.
package functions;
import java.awt.Color;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import javax.swing.JTextField;
public class TextField extends JTextField {
private String hint;
private Color cForeground;
private Color cHint;
public void setHint(String s) {
hint = s;
cForeground = getForeground();
setText(hint);
cHint = new Color(cForeground.getRed(), cForeground.getGreen(),
cForeground.getBlue(), cForeground.getAlpha() / 2);
addFocusListener(new FocusListener() {
#Override
public void focusLost(FocusEvent arg0) {
if (getText().equals("")) {
setForeground(cHint);
setText(hint);
}
}
#Override
public void focusGained(FocusEvent arg0) {
if (getText().equals(hint)) {
setText("");
setForeground(cForeground);
}
}
});
}
}
1) At the moment my hint only shows up when it's not focused. But I want my hint to be visible when it's empty - also when it's focused. I played around with ActionListener instead of FocusListener, but I didn't get it.
2) I want the same thing for JPasswordField, but I don't want to write the same method in 2 different classes. Is there a way I can point at the same method from both classes while one extends JTextField and the other one JPasswordField?
3) I decide whether the hint shall be shown by calling getText(), but that's not nice in handling with passwords (I don't want to get blamed for logging them...). Is there another way wich would prevent this?
Btw: I know about TextPrompt, but I want to build an own simple solution.

As I understand, you want a thing called placeholder in HTML. Then override paintComponent method like this:
public class STextField extends JTextField{
public static final Color placeholderColor = new Color(cForeground.getRed(), cForeground.getGreen(), cForeground.getBlue(), cForeground.getAlpha() / 2);
public STextField(String placeholder){
this.placeholder = placeholder;
}
protected void paintComponent(final Graphics pG) {
super.paintComponent(pG);
if(placeholder.length() == 0 || getText().length() > 0)
return;
final Graphics2D g = (Graphics2D) pG;
g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g.setColor(placeholderColor);
int offset = 4; // This value depends on height of text field. Probably can be calculated from font size.
g.drawString(placeholder, getInsets().left, pG.getFontMetrics().getMaxAscent() + offset);
}
private String placeholder;
}

Java swing component to show image grid

Its been a while since i built a desktop JAVA application.. after lots of documentation and doing implementation tests, i still have not found an image grid solution.
Either Java lacks such a ready-to-use component (?!) or you tell me to brush up my google-fu. :)
I have a very simple technical premises: a JDialog that allows the user to pick an image. Input is a Map<Integer, String> list that holds filenames. Output is the Integer key the user chose. GUI also is simple: user chooses 1 image using mouse or keyboard, and dialog closes. All images are 80x80px and loaded from filename, not a resource.
I tried several approaches so far this morning:
Search for components/widgets that show scrollable imagegrid that can flow to the left. (no dice)
Search for components/widgets that show scrollable imagegrid (no dice)
Search for any components/widgets/gui-libs (no dice .. do these even exist?!)
Try and implement myJList.setModel(), but i cant get it to just take my Map<> and show thumbnails. (overcomplicates!)
Try and implement myJPanel.setlayout(new FlowLayout(..)) with several myJPanel.add(new JButton(..)) which just creates a bunch of JButton on a JPanel, which each need a event handler. I wonder how scrolling and keyboard input is going to work out, and how i'm supposed to keep/reference my Map<> key values. (overcomplicates?)
In lieu of your answer, i am now working on the latter, which should work but i cant believe everyone needs to reinvent the same GUI wheel here. How to have the user select an image from my Map<Integer, String>? Are there JAVA libraries/widgets/components that i should look to avoid this?
I hope this isn't being modded down, i have no working implementation with error to show you guys.. this question is about how/where to find the components or what approaches would be better. Its 2014 and i cant believe that JAVA still requires me to build my own "GUI component" just to see some images.. not even Delphi or Mono does that.

If all you want is a grid of images, and having them selectable, consider using a JList, filling it with appropriate ImageIcons, and giving it a ListSelectionListener. In the Listener you can close the enclosing dialog when a selection has been made.
You state:
Try and implement myJList.setModel(), but i cant get it to just take my Map<> and show thumbnails. (overcomplicates!)
You need to use your Map to populate your ListModel, and set that Model to the JList's model.
For example:
import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Dialog.ModalityType;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.*;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;
#SuppressWarnings("serial")
public class ImageGridPanel extends JPanel {
public static final String PATH = "http://images-2.drive.com.au/2011/";
public static final String[] CARS = {
"04/15/2308961/giulietta_1024-80x80.jpg",
"11/18/2781958/audi-a1-sportback_600-80x80.jpg",
"12/23/2856762/fiat-500-80x80.jpg",
"01/12/2129944/Honda-Civic-Sedan-concept-1_600-80x80.jpg",
"12/23/2856581/mini-roadster-80x80.jpg",
"12/23/2856571/hyundai-veloster-80x80.jpg",
"12/23/2856771/hyundai-i30-80x80.jpg",
"12/23/2856580/mini-coupe-80x80.jpg" };
private DefaultListModel<Car> carModel = new DefaultListModel<>();
final JTextField textField = new JTextField(20);
public ImageGridPanel() {
for (String carPath : CARS) {
String path = PATH + carPath;
try {
URL imgUrl = new URL(path);
BufferedImage img = ImageIO.read(imgUrl);
ImageIcon icon = new ImageIcon(img);
String name = carPath.substring(carPath.lastIndexOf("/"));
name = name.substring(1, name.lastIndexOf("-"));
carModel.addElement(new Car(name, icon));
} catch (IOException e) {
e.printStackTrace();
System.exit(-1);
}
}
ShowGridAction showAction = new ShowGridAction("Car Grid", carModel);
JButton showGridBtn = new JButton(showAction);
add(showGridBtn);
add(textField);
}
private class ShowGridAction extends AbstractAction {
private CarGridPanel carGridPanel;
public ShowGridAction(String name, DefaultListModel<Car> carModel) {
super(name);
carGridPanel = new CarGridPanel(carModel);
}
public CarGridPanel getCarGridPanel() {
return carGridPanel;
}
#Override
public void actionPerformed(ActionEvent e) {
Window win = SwingUtilities.getWindowAncestor((Component) e.getSource());
JDialog dialog = new JDialog(win, "Cars", ModalityType.APPLICATION_MODAL);
dialog.add(carGridPanel);
dialog.pack();
dialog.setLocationRelativeTo(null);
int x = dialog.getLocation().x;
int y = dialog.getLocation().y - 150;
dialog.setLocation(x, y);
dialog.setVisible(true);
Car selectedCar = carGridPanel.getSelectedCar();
if (selectedCar != null) {
textField.setText(selectedCar.getName());
}
}
}
private static void createAndShowGui() {
JFrame frame = new JFrame("ImageGrid");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new ImageGridPanel());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
class Car {
String name;
Icon icon;
public Car(String name, Icon icon) {
this.name = name;
this.icon = icon;
}
public String getName() {
return name;
}
public Icon getIcon() {
return icon;
}
}
#SuppressWarnings("serial")
class CarGridPanel extends JPanel {
private JList<Car> carList = new JList<>();
private Car selectedCar;
public CarGridPanel(ListModel<Car> model) {
carList.setModel(model);
carList.setLayoutOrientation(JList.HORIZONTAL_WRAP);
carList.setVisibleRowCount(2);
carList.setCellRenderer(new DefaultListCellRenderer() {
#Override
public Component getListCellRendererComponent(JList<?> list,
Object value, int index, boolean isSelected, boolean cellHasFocus) {
if (value != null) {
Car carValue = (Car) value;
value = carValue.getIcon();
} else {
value = "";
}
return super.getListCellRendererComponent(list, value, index,
isSelected, cellHasFocus);
}
});
setLayout(new BorderLayout());
add(new JScrollPane(carList));
carList.addListSelectionListener(new ListListener());
}
public Car getSelectedCar() {
return selectedCar;
}
private class ListListener implements ListSelectionListener {
#Override
public void valueChanged(ListSelectionEvent e) {
selectedCar = carList.getSelectedValue();
Window win = SwingUtilities.getWindowAncestor(CarGridPanel.this);
win.dispose();
}
}
}

No, Java doesn't have what you want.
Java is a general-purpose programming language, not a toolset, particularly not a specialized desktop GUI toolset. This is not a denigration of the language, just a statement of a purpose that it was not developed to fulfill.
If Delphi or Mono or anything has your particular widget, then I suggest you program in that, instead. This is not a denigration of you, just an observation that, if you do not want to put together the widget you want from lower-level components and code, then Java is not the right language/tool for you to use to do it.
As for not believing that Java "still requires" you to build your own component, I can only say that you don't get to choose which languages provide which features. I'm just as glad Java isn't littered with your component and the hundreds of others that people like you would come up with that they think Java should provide. It's big enough as it is.

Update JFrame paintings

I want to update my rectangle when my key is pressed currently I have almost achieved that
package com.raggaer.frame;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
public class Elements extends JPanel {
private static int y = 250;
public Elements() {
this.getInputMap().put(KeyStroke.getKeyStroke("UP"), "up");
this.getActionMap().put("up", new Listener("up"));
this.getInputMap().put(KeyStroke.getKeyStroke("DOWN"), "down");
this.getActionMap().put("down", new Listener("down"));
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawRect(250, this.y, 10, 10);
}
public Dimension getPreferredSize() {
return new Dimension(500, 500);
}
public static void setY(int cord) {
y += cord;
// Cant access repaint()
}
}
And this is my listener class
package com.raggaer.frame;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.AbstractAction;
public class Listener extends AbstractAction {
private String code;
//final Elements game = new Elements();
public Listener(String order) {
this.code = order;
}
public void actionPerformed(ActionEvent e) {
System.out.println(this.code);
Elements.setY(1);
}
}
Currently everything works except that I dont know how to update the y position of the rectangle, I tried using an static variable but then I cant call the repaint() method.

No,.... don't use static anything, neither methods nor fields because if you do this, you'll break object-oriented programming rules, leaving your code difficult to update and maintain. The exception of course would be your main method, and carefully chosen fields and methods who truly belong to the class. Instead give the class that needs to call the Element object's method a valid reference to the object whose state you wish to change, the drawing JPanel or Element object. This can be done by passing in a valid reference via a constructor parameter.
public class Listener extends AbstractAction {
private Elements elements;
public Listener(Elements elements) {
this.elements = elements;
}