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Changing the state (the pieces on the board) of a chess game

I'm trying to make a Chess Game, I'm stuck with this:
I create a bunch of panels each one has a label that has an icon (piece icon) with a loop for every panel to represent a case in the game. How can I delete an icon from the last position after the user drags the piece to a new position?
import ma.jerroudi.cheesegame.bouard.Bouard;
import ma.jerroudi.cheesegame.bouard.Case;
import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
public class CheeseGameGui extends JFrame {
Point prevPt;
Point currentPt;
public CheeseGameGui() {
Bouard bouard = new Bouard();
addMouseListener(new MouseAdapter() {
#Override
public void mousePressed(MouseEvent eP) {
prevPt = eP.getPoint();
System.out.println(" x: " + eP.getX() + " y: " + eP.getY());
System.out.println("tab[" + (int) prevPt.getX() / 50 + "] [" + (int) prevPt.getY() / 50 + "]");
}
#Override
public void mouseReleased(MouseEvent eR) {
currentPt = eR.getPoint();
System.out.println(" x: " + eR.getX() + " y: " + eR.getY());
bouard.caseChange((int) prevPt.getY() / 50, (int) prevPt.getX() / 50, (int) currentPt.getY() / 50, (int) currentPt.getX() / 50);
System.out.println("piece name : " + bouard.getCase((int) currentPt.getY() / 50, (int) currentPt.getX() / 50).getSymbol());
}
});
this.setTitle("jeroudi cheese game");
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
ImageIcon image = new ImageIcon("logo.jpg");
this.setIconImage(image.getImage());
for (int i = 0; i <= Bouard.MAX_SIZE; i++) {
for (int j = 0; j <= Bouard.MAX_SIZE; j++) {
JPanel mypanel = new JPanel();
this.add(mypanel);
JLabel labelImg = new JLabel();
int xIndice = j * 50;
int yIndice = i * 50;
mypanel.setBounds(xIndice, yIndice, 50, 50);
mypanel.setBorder(BorderFactory.createLineBorder(Color.green));
ImageIcon pieceImg = new ImageIcon(new ImageIcon(bouard.getCase(i, j).getPiecePhat()).getImage().getScaledInstance(50, 50, Image.SCALE_DEFAULT));
labelImg.setIcon(pieceImg);
mypanel.add(labelImg);
this.getContentPane().add(mypanel);
}
}
setSize(450, 450);
setLayout(null);
this.setUndecorated(true);
setVisible(true);
}
}

setLayout(null); Don't do this. Instead, set a GridLayout to the chessboard (a single JPanel).
Don't add labels to panels then add the panels to the chessboard, simply add the 'labels' directly to the one chessboard panel. But make them undecorated buttons (JButton).
Important
Keep a reference to the buttons in an array (JButton[8][8]).
Establish a ChessModel which encapsulates the state of a chess game and a method to configure the GUI (the button icons) to match the model.
When the user (or their opponent) moves a piece, update the model then refresh the chessboard.
Oh, and now the GUI is laid out, instead of the (wrong) guess setSize(450, 450);, simply call pack() for the right sized GUI. For more on laying out the chessboard, see Making a robust, resizable Swing Chess GUI.

How to combine images in a JFrame?

I have been working on a project that is displaying a grid 16 x 16 of images, based on user interaction this grid follows the user on a dynamically larger base (an example would be a base that is 50 x 50) than the 16 x 16 display.
However, I am using JLabel components to display these images, and every time the user interacts I have to move each of the 256 images and erase the ones that are no longer in the 16 x 16 display grid. This results in a lag that is close to a second per key press and is close to nonfunctional.
What I am looking to try to do is to chain these images together in the total width of the ground and simply move the focus to the portion that is within the 16 x 16 grid, making the process no longer have to use nested for loops for the display.
Is it possible that I could dynamically store and create these chained images for display using a label? If are there other ways to display .png files in Java that could be stored and used in a similar manner?
An example of my current methodology of having to draw every image upon every user interaction:
User user = game.user;
int floorWidth = game.floorWidth;
int floorHeight = game.floorHeight;
int pX = user.getTile().getX();
int pY = user.getTile().getY();
int minX = Math.max(pX - GameConstants.USER_DRAW_DISTANCE, 0);
int maxX = Math.min(floorWidth, pX + GameConstants.USER_DRAW_DISTANCE);
int minY = Math.max(pY - GameConstants.USER_DRAW_DISTANCE, 0);
int maxY = Math.min(floorHeight, pY + GameConstants.USER_DRAW_DISTANCE);
for (int i = minY; i < maxY; i++)
{
for (int x = minX; x < maxX; x++)
{
Tile tile = floor.getTile(x, i);
if (tile.getHasSeen())
{
JLabel cLabel = tile.imageLabel;
cLabel.setLocation(340 + x * 32, 140 + i * 32);
cLabel.setSize(64, 64);
cLabel.setVisible(true);
panel.add(cLabel, 1);
}
}
}

In principle your idea should work. So you're probably doing something else wrong.
I've made an example, where it displays a 16x16 square of JLabels out of 256x256 JLabels. When you move the mouse over the panel, it changes the layout to show a new set of 16x16 JLabels. The change is pretty snappy, definitely not a 1 second delay.
import javax.swing.*;
import java.awt.EventQueue;
import java.awt.Dimension;
import java.awt.Color;
import java.awt.event.*;
import java.util.*;
public class GridViewer{
int x0, y0;
int N = 256;
int display = 16;
int length = 32;
List<JLabel> showing = new ArrayList<>();
List<JLabel> available = new ArrayList<>();
JPanel panel = new JPanel(){
Dimension sz = new Dimension(length*display, length*display);
#Override
public Dimension getPreferredSize(){
return sz;
}
};
public void showGui(){
JFrame frame = new JFrame();
panel.setLayout(null);
panel.addMouseMotionListener( new MouseAdapter(){
Random r = new Random();
#Override
public void mouseMoved(MouseEvent evt){
int x = evt.getX();
int y = evt.getY();
//map to position on the image to the position on the grid.
x0 = x/2;
x0 = Math.min(x0, N-display);
y0 = y/2;
y0 = Math.min(y0, N-display);
updateLayout();
}
});
for(int i = 0; i<N*N; i++){
available.add(createItem(i));
}
updateLayout();
frame.setContentPane(panel);
frame.pack();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
/**
* Creates a solid color jlabel, could be used to load an image
* as an icon.
**/
JLabel createItem(int i){
JLabel l = new JLabel("");
int r = (i/256);
int g = (0)&255;
int b = (i%256);
int c = (r << 16 ) + ( g << 8 ) + b;
l.setBackground(new Color(c));
l.setOpaque(true);
l.setSize(length, length);
return l;
}
public void updateLayout(){
for(JLabel l: showing){
panel.remove(l);
}
for(int i = 0; i<display; i++){
for(int j = 0; j<display; j++){
JLabel l = available.get((i + x0) + (j+y0)*N);
panel.add(l);
l.setLocation( i*length, j*length);
showing.add(l);
}
}
}
public static void main(String[] args){
EventQueue.invokeLater( () -> new GridViewer().showGui() );
}
}
Some variations.
Use a GridLayout
Using a layout manager has a lot of advantages. Especially when it comes to using different displays, fonts and platforms? When adding and removing elements, it could make partially showing elements tough.
Use a large JPanel with a ScrollPane
We could create a single JPanel and add all 256x256 components to it, then use a scroll pane to set the view. This would have an advantage of completely separating the layout and the view. Somebody wants a larger window, you don't have to change the layout, the view gets bigger and you just see more of the layout. For 256x256 components, it should perform well but if you have too many components you might want to reconsider it.
Use a JPanel and override paintComponent
This would involve loading your 'png' files as awt Images (probably BufferedImages) and drawing them with the graphics object. You would need to handle all of the layout and rendering. It gives you quite a bit of power over how you want to render your components.

Scrolling through a JPanel within a JScrollingPanel

I'm trying to make a level editor for my platformer game, I want my levels to be 100 by 100 squares.
So far the editor works, but I can't scroll through the JPanel. I've been playing around and I've made a small test class to fiddle with which I'll post. If you run it, all it does it show the grid. However if I swap out two variables (I'll comment where) it can show an image and scroll according to the size of that image.
I want that scrolling ability only for the JPanel, so that I can scroll through my 100 x 100 square level.
import java.awt.BorderLayout;
public class ScrollPaneJ extends JFrame {
// setting the panels
private JPanel contentPane;
private JScrollPane scrollPane;
// dimensions/ variables of the grid
int size = 16;
int startX = 112;
int startY = 48;
int width = 30;
int height = 30;
// this is the grid
String[][] grid = new String[width][height];
// this is from the full editor class
String currentImage = new String("platform");
ImageIcon currentBackIcon = new ImageIcon("Resources/backdirttile.jpg");
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
// adding the scrollpane
ScrollPaneJ frame = new ScrollPaneJ();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public ScrollPaneJ() {
setTitle("Scrolling Pane Application");
setSize(new Dimension(300, 200));
setBackground(Color.gray);
setDefaultCloseOperation(EXIT_ON_CLOSE);
// defining the top and bottom panels, bottom is what I think I'm
// drawing on, top is where the scrollpanel goes, I copied this code
// from the internet and I'm not too sure how it works
JPanel topPanel = new JPanel();
JPanel bottomPanel = new JPanel(new GridLayout());
bottomPanel.setLayout(new BorderLayout());
getContentPane().add(bottomPanel);
topPanel.setLayout(new BorderLayout());
getContentPane().add(topPanel);
// this is the label I was talking about
Icon image = new ImageIcon("src/MenuDesign.jpg");
JLabel label = new JLabel(image);
// Create a tabbed pane
// if you set it to say label instead of bottomPanel, you can scroll
// through the size of the label
scrollPane = new JScrollPane(bottomPanel);
scrollPane.setBounds(40, 40, 100, 100);
// set it label here as well.
scrollPane.getViewport().add(bottomPanel);
// I was hoping this would force the scrollbar in but it does nothing
scrollPane
.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
scrollPane
.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED);
scrollPane.setBounds(50, 30, 300, 50);
JPanel contentPane = new JPanel(null);
contentPane.setPreferredSize(new Dimension(500, 400));
contentPane.add(scrollPane);
topPanel.add(scrollPane, BorderLayout.CENTER);
init();
}
public void init() {
// this sets the grid to empty
for (int x = 0; x < width; x++) {
for (int y = 0; y < height; y++) {
grid[x][y] = "";
}
}
}
#Override
public void paint(Graphics g) {
// this paints the grid
super.paint(g);
Graphics2D g2d = (Graphics2D) g;
g2d.setColor(Color.black);
for (int x = 0; x < width; x++) {
for (int y = 0; y < height; y++) {
g2d.drawRect(x * size + startX, y * size + startY, size, size);
if (grid[x][y].equals("")) {
g2d.drawImage(currentBackIcon.getImage(),
x * size + startX, y * size + startY, null);
}
g2d.setColor(Color.black);
g2d.drawRect((x * size) + 1 + startX, (y * size) + 1 + startY,
size, size);
}
}
}
public void drawTile() {
// this isn't enabled which is why you can't paint the grid, however it
// would change the tile of the square you're mouse is on, to the
// current tile, it works and isn't really important for what i need
// help with
PointerInfo a = MouseInfo.getPointerInfo();
Point b = a.getLocation();
int mouseX = (int) b.getX();
int mouseY = (int) b.getY();
int gMX = ((mouseX - 48) / 16) - 4;
int gMY = ((mouseY - 48) / 16) - 3;
grid[gMX][gMY] = currentImage;
repaint();
}
}

scrollPane.getViewport().add(bottomPanel); should be more like scrollPane.getViewportView(bottomPanel);
You shouldn't be painting directly to the frame, as child components can be painted without the notification to the parents, meaning that what ever you've painted could be partially wiped out. Instead, this kind of painting should be done within a custom component which acts as the JScrollPane's, JViewport's view.
A JScrollPane needs two things, first, the size that the component would like to be (the preferredSize) and the size of the viewport view. If the component doesn't implement the Scrollable interface, then the component's preferredSize is used to determine that as well. This is why a JLabel will work.
A JScrollPane has a JViewport as it's primary child component. The JViewport should only have a single component, typically assigned either via JScrollPane#setViewportView or JViewport#setView methods
See How to Use Scroll Panes for more details
Create a custom component that extends JPanel and override it's getPreferredSize method to return the size of the component you want. Override it's paintComponent method and perform you custom painting their.
Overlaying custom painting ontop of other components is more difficult

You can also add JScrollPane in your panel like this
JPanel p = new JPanel();
add(new JScrollPane(p));

How should I drag a JLabel from one JPanel in a JFrame onto a JTextField in another JPanel in the same JFrame?

In short, I want to set the text of a JLabel to be that of a JTextField in a JPanel (pnlUser) and then drag the JLabel across the screen from JPanel onto another JTextField in another JPanel (pnlGrid).
Here are the details.
I have written a "Solitaire Scrabble" program. The user can either position the text cursor in a grid cell (a JTextField in pnlGrid) and type a letter that is in the list of "User letters" (a JTextField in pnlUser) OR the user can simulate dragging a letter from "User letters" and dropping it into the destination grid cell in pnlGrid.
I say "simulate" because the selected letter is not actually dragged across the screen. I use the mouse pointer HAND_CURSOR to make the drag/drop as real as possible, but I haven't figured out how to make the HAND_CURSOR "grab" the letter and physically drag the letter across the board to its destination.
As it is, the letter is highlighted but left in the "User letters" area while the HAND_CURSOR moves along the grid during the drag operation. When it gets to the destination cell in pnlGrid and the mouse button is released, the letter is erased from "User letters" and suddenly appears in the grid cell.
So the letter is more or less "teleported" (beam me up, Scotty) from "User letters" to a grid cell. This is too abstract. I want the user letter to be at the tip of the HAND_CURSOR's pointing finger and be dragged along the grid into the grid cell where it will be dropped, as shown in the 3 pictures below.
I've successfully made it happen in a small test program (source below) using JLayeredPane, but I can't make it happen in the game. But I knew nothing about JLayeredPane until two days ago so I don't really know what I'm doing. (I adapted an Oracle tutorial program that demos JLayeredPane.)
I just read about the "glass pane" and thought it would maybe be easier to implement until I downloaded the source for that demo, which is quite long, so since it's totally new and will be even harder to adapt.
So I thought before I spend more hours in frustration I should ask:
Is a JLayeredPane or a setGlassPane approach appropriate? Is there an easier or better way to drag a JLabel from one JPanel onto another another JPanel?
(The approach in the program is to determine which "User letter" is being pointed at, store that letter in a JLabel, and then make sure that during mouseDragged the HAND_CURSOR fingertip is right at the bottom center of the letter.)
package mousemoveletter;
import javax.swing.*;
import javax.swing.border.*;
import java.awt.*;
import static java.awt.Color.*;
import java.awt.event.*;
import static javax.swing.SwingUtilities.invokeLater;
public class LayeredPaneDemo extends JPanel
{
private static final int USER7 = 7;
static Cursor HAND = new Cursor(Cursor.HAND_CURSOR);
static Cursor ARROW = new Cursor(Cursor.DEFAULT_CURSOR);
private static JLayeredPane layeredPane;
private static JLabel lblToMove;
private static JPanel pnlUser;
private static JPanel pnlGrid;
private static final JTextField[] txtUser = new JTextField[USER7];
public LayeredPaneDemo() // constructor
{
pnlGrid = new JPanel();
setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS));
layeredPane = new JLayeredPane();
layeredPane.setPreferredSize(new Dimension(240, 240));
pnlGrid.setSize(140, 140);
pnlGrid.setBorder(new EtchedBorder(RED, GREEN));
pnlGrid.setBackground(YELLOW);
lblToMove = new JLabel("XXX");
lblToMove.setSize(new Dimension(40,40));
layeredPane.add(pnlGrid, 0,0);
layeredPane.add(lblToMove, new Integer(0), -1);
add(layeredPane);
}
private static void createAndShowGUI() {
JFrame frame = new JFrame("LayeredPaneDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JComponent newContentPane = new LayeredPaneDemo();
newContentPane.setOpaque(true); //content panes must be opaque
frame.setContentPane(newContentPane);
makeUser();
frame.add(pnlUser);
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
invokeLater(new Runnable()
{
public void run() {
createAndShowGUI();
}
});
}
private static void makeUser(){
pnlUser = new JPanel(new GridLayout(1,USER7));
pnlUser.setPreferredSize(new Dimension(225, 50));
pnlUser.setBackground(Color.green);
pnlUser.setBorder(BorderFactory.createLineBorder(Color.BLUE));
for(int k = 0; k < USER7; k++)
{
txtUser[k] = new JTextField("" + (char)(Math.random()*26+65));
txtUser[k].setName("" + k);
txtUser[k].setEditable(false);
txtUser[k].addMouseMotionListener(new MouseMotionAdapter()
{
public void mouseDragged(MouseEvent e)
{
lblToMove.setCursor(HAND);
int w = Integer.parseInt(e.getComponent().getName());
lblToMove.setText(txtUser[w].getText());
layeredPane.setLayer(lblToMove, 0, 0);
lblToMove.setLocation(e.getX() + (e.getComponent().getWidth())*w,
e.getY() + layeredPane.getHeight() - e.getComponent().getHeight()/2);
};
});
txtUser[k].addMouseListener(new MouseAdapter()
{
public void mouseReleased(MouseEvent e)
{
lblToMove.setCursor(ARROW);
}
});
pnlUser.add(txtUser[k]);
}
}
}

Thanks to #trashgod, I figured it out by following his links to this example and variation; I adapted the drag/drop of the chessboard found there to my own particular needs for "Scrabble".
The code below is not final code for my Solitaire Scrabble program, but proof-of-concept, possibly usable by others wishing to drag a cell from a 1xN grid onto a MxM grid.
package components;
import java.awt.*;
import static java.awt.BorderLayout.NORTH;
import static java.awt.BorderLayout.SOUTH;
import java.awt.event.*;
import static java.lang.Integer.parseInt;
import javax.swing.*;
import static javax.swing.WindowConstants.DISPOSE_ON_CLOSE;
import javax.swing.event.MouseInputAdapter;
public class ChessBoard //implements MouseListener, MouseMotionListener
{
static Point parentLocation;
int homeRow, homeCol; // where to restore moved user letter if dropped on occupied cell
static int N = 11; // NxN 'chessboard' squares
static int S = 44; // square dimensions: SxS
static int W ; // chessboard dimensions: WxW
static int USER7 = 7;
static Font dragFont;
static JFrame frame;
JLayeredPane layeredPane;
static JPanel gamePanel, // encompasses both pnlGrid and pnlUser
pnlGrid,
pnlUser;
JLabel userDragLetter = new JLabel(); // main item to drag around or restore if needed
int xAdjustment, yAdjustment; // how to locate drops accurately
String userLetters[] ;
public ChessBoard() // constructor
{
W = S*N;
dragFont = new Font("Courier", Font.PLAIN, S);
userLetters = new String[USER7];
for (int i = 0; i < USER7; i++)
userLetters[i] = "" + (char)(65 + Math.random()*26);
Dimension gridSize = new Dimension(W, W);
Dimension userSize = new Dimension(W, S);
Dimension gameSize = new Dimension(W, (W + S));
frame = new JFrame();
frame.setSize(new Dimension(gameSize)); // DO NOT USE PREFERRED
layeredPane = new JLayeredPane();
layeredPane.setPreferredSize( gameSize ); // NO PREFERRED => NO GRID!
gamePanel = new JPanel();
// **EDIT** LOSE THIS LINE gamePanel.setLayout(new BorderLayout());
gamePanel.setPreferredSize(gameSize);
pnlGrid = new JPanel();
pnlGrid.setLayout(new GridLayout(N, N));
pnlGrid.setPreferredSize( gridSize );
pnlGrid.setBounds(0, 0, gridSize.width, gridSize.height);
pnlUser = new JPanel();
pnlUser.setLayout(new GridLayout(1, N));
pnlUser.setPreferredSize(userSize);
pnlUser.setBounds(0, gridSize.height, userSize.width, userSize.height);
layeredPane.add(pnlGrid, JLayeredPane.DEFAULT_LAYER); // panels to drag over
layeredPane.add(pnlUser, JLayeredPane.DEFAULT_LAYER); // " "
for (int i = 0; i < N; i++){
for (int j = 0; j < N; j++){
JPanel square = new JPanel();
square.setBackground( (i + j) % 2 == 0 ? Color.red : Color.white );
pnlGrid.add( square );
}
}
for (int i = 0; i < N; i++) {
JPanel square = new JPanel(new BorderLayout());
square.setBackground(Color.YELLOW);
pnlUser.add(square);
}
for (int i = 0; i < USER7; i++)
addPiece(i, 0, userLetters[i]);
gamePanel.addMouseListener(new MouseInputAdapter()
{
public void mousePressed (MouseEvent e){mousePressedActionPerformed (e);}
public void mouseReleased(MouseEvent e){mouseReleasedActionPerformed(e);}
});
gamePanel.addMouseMotionListener(new MouseMotionAdapter()
{
public void mouseDragged(MouseEvent me){mouseDraggedActionPerformed(me);}
});
// **EDIT: LOSE THE NEXT TWO LINES AND REPLACE BY THE LINE AFTER THEM**
// gamePanel.add(layeredPane, NORTH);
// gamePanel.add(pnlUser, SOUTH);
gamePanel.add(layeredPane);
}
private void addPiece(int col, int row, String glyph) {
JLabel piece = new JLabel(glyph, JLabel.CENTER);
piece.setFont(dragFont);
JPanel panel = (JPanel) pnlUser.getComponent(col + row * N);
piece.setName("piece " + glyph + " # " + row + " " + col);
panel.add(piece);
}
void mousePressedActionPerformed(MouseEvent e)
{
userDragLetter = null; // signal that we're not dragging if no piece is in the square
gamePanel.setCursor(new Cursor(Cursor.HAND_CURSOR));
Component c = pnlGrid.findComponentAt(e.getX(), e.getY());
if(c != null)
return; // Illegal to click pnlGrid
c = pnlUser.findComponentAt(e.getX(), e.getY() - pnlGrid.getHeight());
if(c == null | c instanceof JPanel)
return; // letter already played; can't drag empty cell
parentLocation = c.getParent().getLocation();
xAdjustment = parentLocation.x - e.getX();
yAdjustment = parentLocation.y - e.getY() + gamePanel.getHeight() - pnlUser.getHeight();
userDragLetter = (JLabel)c;
userDragLetter.setPreferredSize(new Dimension(S, S)); // prevent 2 letters in a square
userDragLetter.setLocation(e.getX() + xAdjustment, e.getY() + yAdjustment);
layeredPane.add(userDragLetter, JLayeredPane.DRAG_LAYER);
homeRow = parseInt(userDragLetter.getName().substring(10,11)); // save restore location
homeCol = parseInt(userDragLetter.getName().substring(12,13));
}
void mouseDraggedActionPerformed(MouseEvent me)
{
if (userDragLetter == null)
return; // nothing to drag
int x = me.getX() + xAdjustment; // make sure grid cell will be chosen in-bounds
int xMax = layeredPane.getWidth() - userDragLetter.getWidth();
x = Math.min(x, xMax);
x = Math.max(x, 0);
int y = me.getY() + yAdjustment;
int yMax = layeredPane.getHeight() - userDragLetter.getHeight();
y = Math.min(y, yMax);
y = Math.max(y, 0);
if(y >= pnlGrid.getHeight())
return; // can't drag to location off grid
userDragLetter.setLocation(x, y);
}
void mouseReleasedActionPerformed(MouseEvent e)
{
//**EDIT: CHANGED NEXT LINE**
gamePanel.setCursor(Cursor.getPredefinedCursor(Cursor.DEFAULT_CURSOR));
if (userDragLetter == null)
return; // nothing to drag; nothing to release
// Make sure the chess piece is no longer painted on the layered pane
userDragLetter.setVisible(false);
layeredPane.remove(userDragLetter);
userDragLetter.setVisible(true);
int xMax = layeredPane.getWidth() - userDragLetter.getWidth();
int x = Math.min(e.getX(), xMax);
x = Math.max(x, 0);
int yMax = layeredPane.getHeight()- userDragLetter.getHeight();
int y = Math.min(e.getY(), yMax);
y = Math.max(y, 0);
Component c = pnlGrid.findComponentAt(x, y); // find deepest nested child component
if(c == null) // then grid cell is unoccupied so ...
c = pnlUser.findComponentAt(x, y); // see if there's a letter there ...
if(c == null | (c instanceof JLabel)){ // and if illegal or there is one, put it back...
userDragLetter.setLocation(parentLocation.x + xAdjustment,
parentLocation.y + yAdjustment + gamePanel.getHeight());
userDragLetter.setVisible(true);
addPiece(homeCol, homeRow,userDragLetter.getName().substring(6,7));
layeredPane.remove(userDragLetter);
return;
}
else // but if NO letter ...
{
Container parent = (Container)c;
parent.add( userDragLetter ); // put one in the grid cell
parent.validate();
}
userDragLetter.setCursor(Cursor.getPredefinedCursor(Cursor.DEFAULT_CURSOR));
}
public static void main(String[] args)
{
new ChessBoard();
frame.add(gamePanel);
frame.setDefaultCloseOperation( DISPOSE_ON_CLOSE );
// frame.setResizable( false );
frame.pack();
frame.setLocationRelativeTo( null );
frame.setVisible(true);
}
}

JPanel only showing one object

I've made 20 objects from my Ball class, as I need 20 balls bouncing around on the screen, but right now it only shows 1 ball bouncing around.
I think it has something to do with 20 JPanels being added and they are overlapping each other, but I'm not entirely sure.
package com.company;
import javax.swing.*;
import java.awt.*;
import java.util.Random;
/**
* Created by John on 25/02/2015.
*/
public class Ball extends JComponent{
int _speedX;
int _speedY;
int _size;
int _x;
int _y;
Color _color;
int _windowX;
int _windowY;
Ball(int x, int y, int sz, int sX, int sY, Color c, int windowX, int windowY){
_x = x;
_y = y;
_speedX = sX;
_speedY = sY;
_size = sz;
_color = c;
_windowX = windowX;
_windowY = windowY;
setForeground(_color);
}
public void update(){
_x = _x + _speedX;
_y = _y + _speedY;
if (_x<0 || _x>_windowX-_size){
_speedX*=-1;
}
if (_y<=0 || _y>_windowY-_size){
_speedY*=-1;
}
this.repaint();
}
public static int randInt(int min, int max) {
// NOTE: Usually this should be a field rather than a method
// variable so that it is not re-seeded every call.
Random rand = new Random();
// nextInt is normally exclusive of the top value,
// so add 1 to make it inclusive
int randomNum = rand.nextInt((max - min) + 1) + min;
return randomNum;
}
public void paint(Graphics g) {
super.paint(g);
Graphics2D g2d = (Graphics2D) g;
g2d.fillOval(_x, _y, _size, _size);
}
public static void main(String[] args) {
// write your code here
JFrame frame = new JFrame("Title"); //create a new window and set title on window
frame.setSize(600, 600); //set size of window
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //set the window to close when the cross in the corner is pressed
frame.setVisible(true); //make the window visible
JPanel panel = new JPanel();
frame.add(panel);
Ball[] balls = new Ball[20];
for(int i = 0; i<20;i++){
balls[i] = new Ball(randInt(0,600),randInt(0,600),randInt(10,20),randInt(1,8), randInt(1,8),Color.yellow,600,600);
panel.add(balls[i]);
}
while(true){
for(int i = 0; i < balls.length; i++) {
balls[i].update();
}
panel.repaint();
try { Thread.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); }
}
}
}

Suggestions:
Don't make Ball extend JComponent or JPanel, but instead make it a logical non-component class.
Create a Drawing class that extends JPanel and draw in its paintComponent method, not its paint(...) method. This will lead to smoother animation.
Create an ArrayList<Ball> of your Ball objects and draw them inside of the paintComponent(...) method override by iterating through the list.
Same for moving the Balls held by the List.
Use a Swing Timer to drive your animation, not a while (true) loop. If you make one mistake with that loop, you'll freeze your GUI rendering it non-functioning, and so the Swing Timer is a much safer way to do this.

it only shows 1 ball bouncing around.
I'm surprised you even see one. You shouldn't see any.
I think it has something to do with 20 JPanels being added and they are overlapping each other,
The problem is that by default a JPanel uses a FlowLayout. When you add a component to the panel the panel will respect the preferred size of the component. You are using a custom component and the default size is (0, 0) since you didn't provide one.
If you want to continue this approach by using a custom component then you need to:
use the properties of the component to control the size and location of the component on the panel. That is you can use the setSize(...) method and setLocation(...) method. You don't need your _x, _y and _size variables. You also don't need the color variable because you can use setForeground(...) to set the color of your component.
Override the getPreferredSize() method to return the size of the ball.
Override the 'paintComponent(...)` method to fill the oval with an x/y value of 0, since the painting needs to be done relative to the ball, not the panel.
In the update() method you use the setLocation(...) method to set the location of the component on the panel.
Now you also need to use a null layout on your panel so the balls can move randomly.
I don't recommend this approach for your final solution, but it is a good exercise to implement this logic to understand how you might go about creating a custom component and how painting is done on this component. Understanding this concept will help you better understand how Swing works in general.