I am looking to solve the N-Queens problem, and I have pinpointed the issue that I am having. There is a JButton that is pressed to tell the user textually in the frame if their solution is correct or not. This button only seems to work when Queens have not been placed on the board. The problem seems to be the setText() method for my JLabel "ifNotSafe" is not working properly. If I put print statements under that method call, the correct message is sent to the console but the label is not changed. The label weirdly only works when Queens have not been placed on the board yet. There is also a Boxes object with an x value and a y value, and a getter method for each.
import javax.swing.*;
import javax.swing.border.LineBorder;
import java.awt.Color;
import java.awt.GridLayout;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.*;
/*
* Overall class to make the whole ChessBoard and all the helper methods to
* tell the user whether their solution is correct or not
*/
public class ChessBoardGUI extends JFrame {
/**
*
*/
private static final long serialVersionUID = 1L;
//ImageIcon queenP = new //ImageIcon(getClass().getResource("/images/queen.png"));
//Image img = queenP.getImage();
//Image newImg = img.getScaledInstance(40, 40, java.awt.Image.SCALE_SMOOTH);
ImageIcon queenPic = new ImageIcon(newImg);
private static JButton tip;
private static JButton safe;
private static JLabel ifNotSafe;
private JButton[][] chessBoxes = new JButton[8][8];
public static JPanel chessBoard;
public static ArrayList<Boxes> queensOnBoard = new ArrayList<Boxes>();
/*
* Makes the whole frame for the ChessBoard
*/
public ChessBoardGUI() {
createBoard();
createOtherThings();
setSize(500, 500);
}
/*
* Creates the Tip and Safe buttons And Label to display when the solution
* is incorrect
*/
public void createOtherThings() {
safe = new JButton("Safe?");
tip = new JButton("Tip");
ifNotSafe = new JLabel("Status of Board is displayed here...");
ButtonListen1 safeListener = new ButtonListen1();
ButtonListen2 tipListener = new ButtonListen2();
safe.addActionListener(safeListener);
tip.addActionListener(tipListener);
}
/*
* ActionListener for the safe button
*/
class ButtonListen1 implements ActionListener {
@Override
public void actionPerformed(ActionEvent e) {
// Tells user which queens are not safe
if (checkSolution(queensOnBoard) == true) {
//****THIS IS WHERE THE PROBLEM IS *******
ifNotSafe.setText("This Solution is correct so far");
System.out.println("Solution is correct");
} else{
ifNotSafe.setText("This Solution is incorrect so far");
// *********Also highlight the queens that are not safe******
System.out.println("Solution is incorrect");
}
}
}
/*
* ActionListener for the tip button
*/
class ButtonListen2 implements ActionListener {
@Override
public void actionPerformed(ActionEvent e) {
// ********Tells the user other places to put queens********
}
}
/*
* Creates the overall ChessBoard
*/
public void createBoard() {
GridLayout gridLayout = new GridLayout();
gridLayout.setRows(8);
gridLayout.setColumns(8);
chessBoard = new JPanel(gridLayout);
chessBoard.setSize(400, 400);
chessBoard.setBorder(new LineBorder(Color.BLACK));
chessBoard.setVisible(true);
/*
* Loops through to add each chessBox to the chessBoard
*/
for (int x = 0; x < 8; x++) {
for (int y = 0; y < 8; y++) {
chessBoxes[x][y] = new JButton();
chessBoxes[x][y].setBorderPainted(false);
/*
* Assigns a color to every other box
*/
if ((x + y) % 2 == 0) {
chessBoxes[x][y].setBackground(Color.BLACK);
} else {
chessBoxes[x][y].setBackground(Color.WHITE);
}
chessBoxes[x][y].setOpaque(true);
chessBoard.add(chessBoxes[x][y]);
// Adds the ActionListener to each chessBox
BoxListener boxListen = new BoxListener();
chessBoxes[x][y].addActionListener(boxListen);
}
}
}
/*
* Action Listener for if the individual boxes on the ChessBoard are clicked
*/
class BoxListener implements ActionListener {
@Override
public void actionPerformed(ActionEvent e) {
JButton button = ((JButton) e.getSource());
// Runs through a loop to find the X and Y coordinate of the
// JButton(Box) that was clicked
for (int x = 0; x < 8; x++) {
for (int y = 0; y < 8; y++) {
if (chessBoxes[x][y] == button) {
/*
* If there is No Queen at that JButton
*/
if ((isOnBoard(queensOnBoard, x, y) == false)) {
// Makes sure the user can not place more than
// 8 Queens on the board
if (queensOnBoard.size() < 8) {
// Sets Picture of Queen on box
//button.setIcon(queenPic);
button.setText("Occupied");
// Adds box to the ArrayList of occupied boxes
queensOnBoard.add(new Boxes(x, y));
}
}
/*
* If there is a Queen at that JButton
*/
else {
removeQueen(queensOnBoard, x, y);
//button.setIcon(null);
button.setText("");
}
}
}
}
}
}
/*
* Checks if a certain Box has a Queen in it or not
*
* @param a Is the ArrayList of the Boxes currently occupied by Queens
*
* @param x Is the X coordinate of the Box that was clicked
*
* @param y Is the Y coordinate of the Box that was clicked
*/
public boolean isOnBoard(ArrayList<Boxes> a, int x, int y) {
for (int i = 0; i < a.size(); i++) {
if (((a.get(i)).getX() == x) && ((a.get(i)).getY() == y)) {
return true;
}
}
return false;
}
/*
* Removes a Queen from the GUI at the specified Box (JButton)
*
* @param a Is the ArrayList of the Boxes currently occupied by Queens
*
* @param x Is the X coordinate of the Box that was clicked
*
* @param y Is the Y coordinate of the Box that was clicked
*/
public void removeQueen(ArrayList<Boxes> a, int x, int y) {
/*
* Removes the box from the overall ArrayList of Boxes Occupied by
* queens according to the x and y location
*/
for (int i = 0; i < a.size(); i++) {
if (((a.get(i)).getX() == x) && ((a.get(i)).getY() == y)) {
queensOnBoard.remove(i);
}
}
}
/*
* Return to the user which queens need to be highlighted
*
* @param queensOnBoard Is the ArrayList of Boxes that are occupied by
* Queens currently on the ChessBoard
*/
public void conflictingQueens(ArrayList<Boxes> queensOnBoard) {
// *******Call the highlightBoxes method using the ArrayList
// Of Boxes you get from this method
}
/*
* Checks to see if solution is correct thusfar
*
* @param queensOnBoard Is the ArrayList of Boxes that are occupied by
* Queens currently on the ChessBoard
*/
public boolean checkSolution(ArrayList<Boxes> queensOnBoard) {
int size = queensOnBoard.size();
if (size < 1) {
return true;
}
if (size == 1) {
return true;
}
for (int x = 0; x < size - 1; x++) {
for (int y = 1; y < size; y++) {
// Checks if Queen is safe from horizontal attacks
if (queensOnBoard.get(x).getX() == queensOnBoard.get(y).getX()) {
return false;
// Checks if Queen is safe from vertical attacks
} else if (queensOnBoard.get(x).getY() == queensOnBoard.get(y).getY()) {
return false;
// Checks if Queen is safe from diagonal attacks
// Uses diagonalAttack(queensOnBoard) as a helper method
} // else if(){
// return false;
// }
}
}
return true;
}
/*
* Checks to see if the queen is safe from diagonal attacks
*
*
*/
// public boolean diagonalAttack(ArrayList<Boxes> queensOnBoard){
//********
// }
/*
* Highlights boxes that are conflicting with one another
*
* @param highlight Is the ArrayList of Boxes that are occupied by Queens
* currently on the ChessBoard
*/
public void highlightBoxes(ArrayList<Boxes> highlight) {
int size1 = highlight.size();
int size2 = queensOnBoard.size();
// When there aren't any queens at risk, this block
// changes the background colors of the boxes back to
// Their respective color
if ((size1 == 0) && size1 == 1) {
for (int x = 0; x < 8; x++) {
for (int y = 0; y < 8; y++) {
chessBoxes[x][y] = new JButton();
chessBoxes[x][y].setBorderPainted(false);
/*
* Assigns a color to every other box
*/
if ((x + y) % 2 == 0) {
chessBoxes[x][y].setBackground(Color.BLACK);
} else {
chessBoxes[x][y].setBackground(Color.WHITE);
}
}
}
}
// Runs through both the highlight and queensOnBoard ArrayLists and
// changes the background for the Queens at risk
for (int b = 0; b < size2; b++) {
for (int a = 0; a < size1; a++) {
if ((highlight.get(a).getX() == queensOnBoard.get(b).getX())
&& (highlight.get(a).getY() == queensOnBoard.get(b).getY())) {
int x = queensOnBoard.get(b).getX();
int y = queensOnBoard.get(b).getY();
chessBoxes[x][y].setBackground(Color.RED);
}
}
}
}
/*
* Main method to run the program
*
* @param args Is the String of args given to the console to run the
* operations of the program
*/
public static void main(String[] args) {
JFrame frame = new ChessBoardGUI();
frame.add(chessBoard);
chessBoard.setLocation(50, 50);
JPanel panel1 = new JPanel();
panel1.add(ifNotSafe);
panel1.add(safe);
panel1.add(tip);
frame.add(panel1);
frame.setTitle("ChessBoard");
frame.setVisible(true);
frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
}
}
You may have a layout problem in that your JLabel doesn't show well because the JPanel that holds it has been added incorrectly to the GUI. Understand that a JFrame's contentPane uses BorderLayout by default, and so when adding components to it, you should specify the BorderLayout location that the component should be placed in. The grid will be placed BorderLayout.CENTER, and panel1 should be placed BorderLayout.PAGE_START. Also, the grid's preferred size should be set, and you should call pack() on your JFrame after adding all components but before making it visible or setting its location.
Other minor quibbles:
Test code is below. Note that I don't have your queen images available so I created a method that you won't need, private Icon createQueenIcon(). This way your code will run on my system. Also to make the code run and compile, I created and included the necessary Boxes class. In the future, be sure that you include all that is needed for us to be able to compile and run your code!
import javax.swing.*;
import javax.swing.border.LineBorder;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.Image;
import java.awt.RenderingHints;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.util.*;
public class ChessBoardGUI extends JFrame {
private static final long serialVersionUID = 1L;
// !! code changes below only to allow me to run your code without
// your images. !!
// ImageIcon queenP = new ImageIcon(getClass().getResource("/images/queen.png"));
// Image img = queenP.getImage();
// Image newImg = img.getScaledInstance(40, 40,
// java.awt.Image.SCALE_SMOOTH);
private ImageIcon queenPic = createQueenIcon(); //!! delete this
// all fields should be private and non-static
private JButton tip;
private JButton safe;
private JLabel ifNotSafe;
private JButton[][] chessBoxes = new JButton[8][8];
private JPanel chessBoard;
private ArrayList<Boxes> queensOnBoard = new ArrayList<Boxes>();
public ChessBoardGUI() {
createBoard();
add(chessBoard, BorderLayout.CENTER); // Do this here
// !! createOtherThings(); // get rid of -- put in constructor
safe = new JButton("Safe?");
tip = new JButton("Tip");
ifNotSafe = new JLabel("Status of Board is displayed here...");
ButtonListen1 safeListener = new ButtonListen1();
ButtonListen2 tipListener = new ButtonListen2();
safe.addActionListener(safeListener);
tip.addActionListener(tipListener);
// !! add the panel1 here!
JPanel panel1 = new JPanel();
panel1.add(ifNotSafe);
panel1.add(safe);
panel1.add(tip);
add(panel1, BorderLayout.PAGE_START); // using BorderLayout constants
// !! setSize(500, 500);
}
// !! so I can use images without having an image
// !! you won't need this
private Icon createQueenIcon() {
int w = 40;
BufferedImage img2 = new BufferedImage(w, w, BufferedImage.TYPE_INT_ARGB);
Graphics2D g2 = img2.createGraphics();
g2.setColor(new Color(183, 65, 14));
g2.fillRect(0, 0, w, w);
g2.setColor(new Color(255, 215, 0));
Font font = new Font(Font.SANS_SERIF, Font.BOLD, 30);
g2.setFont(font);
g2.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING,
RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
FontMetrics fontMetrics = g2.getFontMetrics();
int textX = (w - fontMetrics.charWidth('Q')) / 2;
int textY = (w - fontMetrics.getHeight()) / 2 + fontMetrics.getAscent();
g2.drawString("Q", textX, textY);
g2.dispose();
return new ImageIcon(img2);
}
class ButtonListen1 implements ActionListener {
@Override
public void actionPerformed(ActionEvent e) {
if (checkSolution(queensOnBoard) == true) {
// ****THIS IS WHERE THE PROBLEM IS ******* !!
ifNotSafe.setText("This Solution is correct so far");
System.out.println("Solution is correct");
} else {
ifNotSafe.setText("This Solution is incorrect so far");
// *********Also highlight the queens that are not safe******
System.out.println("Solution is incorrect");
}
}
}
/*
* ActionListener for the tip button
*/
class ButtonListen2 implements ActionListener {
@Override
public void actionPerformed(ActionEvent e) {
}
}
/*
* Creates the overall ChessBoard
*/
public void createBoard() {
GridLayout gridLayout = new GridLayout();
gridLayout.setRows(8);
gridLayout.setColumns(8);
chessBoard = new JPanel(gridLayout);
chessBoard.setPreferredSize(new Dimension(640, 640));
chessBoard.setBorder(new LineBorder(Color.BLACK));
chessBoard.setVisible(true);
for (int x = 0; x < 8; x++) {
for (int y = 0; y < 8; y++) {
chessBoxes[x][y] = new JButton();
chessBoxes[x][y].setBorderPainted(false);
if ((x + y) % 2 == 0) {
chessBoxes[x][y].setBackground(Color.BLACK);
} else {
chessBoxes[x][y].setBackground(Color.WHITE);
}
chessBoxes[x][y].setOpaque(true);
chessBoard.add(chessBoxes[x][y]);
BoxListener boxListen = new BoxListener();
chessBoxes[x][y].addActionListener(boxListen);
}
}
}
class BoxListener implements ActionListener {
@Override
public void actionPerformed(ActionEvent e) {
JButton button = ((JButton) e.getSource());
for (int x = 0; x < 8; x++) {
for (int y = 0; y < 8; y++) {
if (chessBoxes[x][y] == button) {
if ((isOnBoard(queensOnBoard, x, y) == false)) {
if (queensOnBoard.size() < 8) {
button.setIcon(queenPic);
queensOnBoard.add(new Boxes(x, y));
}
}
/*
* If there is a Queen at that JButton
*/
else {
removeQueen(queensOnBoard, x, y);
button.setIcon(null);
}
}
}
}
}
}
/*
* Checks if a certain Box has a Queen in it or not
*
* @param a Is the ArrayList of the Boxes currently occupied by Queens
*
* @param x Is the X coordinate of the Box that was clicked
*
* @param y Is the Y coordinate of the Box that was clicked
*/
public boolean isOnBoard(ArrayList<Boxes> a, int x, int y) {
for (int i = 0; i < a.size(); i++) {
if (((a.get(i)).getX() == x) && ((a.get(i)).getY() == y)) {
return true;
}
}
return false;
}
/*
* Removes a Queen from the GUI at the specified Box (JButton)
*
* @param a Is the ArrayList of the Boxes currently occupied by Queens
*
* @param x Is the X coordinate of the Box that was clicked
*
* @param y Is the Y coordinate of the Box that was clicked
*/
public void removeQueen(ArrayList<Boxes> a, int x, int y) {
/*
* Removes the box from the overall ArrayList of Boxes Occupied by
* queens according to the x and y location
*/
for (int i = 0; i < a.size(); i++) {
if (((a.get(i)).getX() == x) && ((a.get(i)).getY() == y)) {
queensOnBoard.remove(i);
}
}
}
/*
* Return to the user which queens need to be highlighted
*
* @param queensOnBoard Is the ArrayList of Boxes that are occupied by
* Queens currently on the ChessBoard
*/
public void conflictingQueens(ArrayList<Boxes> queensOnBoard2) {
}
/*
* Checks to see if solution is correct thusfar
*
* @param queensOnBoard Is the ArrayList of Boxes that are occupied by
* Queens currently on the ChessBoard
*/
public boolean checkSolution(ArrayList<Boxes> queensOnBoard2) {
int size = queensOnBoard2.size();
if (size < 1) {
return true;
}
if (size == 1) {
return true;
}
for (int x = 0; x < size - 1; x++) {
for (int y = 1; y < size; y++) {
if (queensOnBoard2.get(x).getX() == queensOnBoard2.get(y).getX()) {
return false;
} else if (queensOnBoard2.get(x).getY() == queensOnBoard2.get(y).getY()) {
return false;
}
}
}
return true;
}
/*
* Checks to see if the queen is safe from diagonal attacks
*/
/*
* Highlights boxes that are conflicting with one another
*
* @param highlight Is the ArrayList of Boxes that are occupied by Queens
* currently on the ChessBoard
*/
public void highlightBoxes(ArrayList<Boxes> highlight) {
int size1 = highlight.size();
int size2 = queensOnBoard.size();
if ((size1 == 0) && size1 == 1) {
for (int x = 0; x < 8; x++) {
for (int y = 0; y < 8; y++) {
chessBoxes[x][y] = new JButton();
chessBoxes[x][y].setBorderPainted(false);
/*
* Assigns a color to every other box
*/
if ((x + y) % 2 == 0) {
chessBoxes[x][y].setBackground(Color.BLACK);
} else {
chessBoxes[x][y].setBackground(Color.WHITE);
}
}
}
}
for (int b = 0; b < size2; b++) {
for (int a = 0; a < size1; a++) {
if ((highlight.get(a).getX() == queensOnBoard.get(b).getX())
&& (highlight.get(a).getY() == queensOnBoard.get(b).getY())) {
int x = queensOnBoard.get(b).getX();
int y = queensOnBoard.get(b).getY();
chessBoxes[x][y].setBackground(Color.RED);
}
}
}
}
public static void main(String[] args) {
// !! create the GUI in a Swing thread-safe manner
SwingUtilities.invokeLater(() -> createGui());
}
public static void createGui() {
JFrame frame = new ChessBoardGUI();
// !! frame.add(chessBoard); // not here
// !! chessBoard.setLocation(50, 50);
// !! this does not belong within main
// !! JPanel panel1 = new JPanel();
// panel1.add(ifNotSafe);
// panel1.add(safe);
// panel1.add(tip);
// frame.add(panel1);
frame.setTitle("ChessBoard");
frame.pack(); // !! call this to have your GUI size itself
frame.setLocationRelativeTo(null);
frame.setVisible(true);
frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
}
private static class Boxes {
private int x;
private int y;
public Boxes(int x, int y) {
this.x = x;
this.y = y;
}
public int getY() {
return x;
}
public int getX() {
return y;
}
}
}