在JPanel之上添加JLabel

Question

I attempting to place a .jpg icon on top of a JPanel in order to represent a board piece on a board. I have a GUI folder with the .java files and another folder containing the .jpg files.

--Major Edit-- Example Code

When a square is clicked a white icon is meant to be placed then black etc etc. This is a very basic example of what im trying to achieve

import java.awt.Dimension;

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class gui extends JFrame implements MouseListener {

/**
 * 
 */
private static final long serialVersionUID = -973341728129968945L;
JLayeredPane layeredPane;
JPanel board;
JLabel piece;
int numSquares;
private boolean currentPlayer;

public gui(){

    Dimension boardSize = new Dimension(600, 600);

    numSquares = 6;
    currentPlayer = true;

    layeredPane = new JLayeredPane();
    getContentPane().add(layeredPane);
    layeredPane.setPreferredSize(boardSize);
    layeredPane.addMouseListener(this);

    board = new JPanel();
    layeredPane.add(board, JLayeredPane.DEFAULT_LAYER);

    board.setLayout( new GridLayout(numSquares, numSquares) );
    board.setPreferredSize( boardSize );
    board.setBounds(0, 0, boardSize.width, boardSize.height);

    for (int i = 0; i < (numSquares * numSquares); i++) {
        JPanel square = new JPanel( new BorderLayout() );
        square.setBorder(BorderFactory.createLineBorder(Color.black));
        square.setBackground(Color.green);
        board.add( square );


     }



}

public static void main(String[] args) {
        JFrame frame = new gui();
        frame.setDefaultCloseOperation(DISPOSE_ON_CLOSE );
        frame.pack();
        frame.setResizable(true);
        frame.setLocationRelativeTo( null );
        frame.setVisible(true);
     }



@Override
public void mouseClicked(MouseEvent e) {
    JPanel temp =  (JPanel)board.findComponentAt(e.getX(), e.getY());
    System.out.println(e.getX() + " " + e.getY());

    if( currentPlayer ){
        ImageIcon white = new ImageIcon("l/Images/white.jpg");
        piece = new JLabel(white);
        temp.add(piece);
    }
    else{   
        ImageIcon black = new ImageIcon( "/Images/black.jpg");
        piece = new JLabel(black);
        temp.add(piece);
    }
    currentPlayer = !currentPlayer;


}


@Override
public void mouseEntered(MouseEvent e) {


}

@Override
public void mouseExited(MouseEvent arg0) {
    // TODO Auto-generated method stub

}

@Override
public void mousePressed(MouseEvent arg0) {
    // TODO Auto-generated method stub

}

@Override
public void mouseReleased(MouseEvent e) {

}




}

Answer 1

Don't forget to revalidate and repaint if adding or removing components from a container. I've modified your SSCCE, and have gotten rid of the need to use images to make it runnable by folks who don't have access to your image files (like me!). Changes are noted by the // !! comments:

import java.awt.Color;
import java.awt.Dimension;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;

public class Gui2 extends JFrame implements MouseListener {

   private static final long serialVersionUID = -973341728129968945L;
   JLayeredPane layeredPane;
   JPanel board;
   JLabel piece;
   int numSquares;
   private boolean currentPlayer;

   // !!
   private ImageIcon whiteIcon;
   private ImageIcon blackIcon;

   public Gui2() {
      // !!
      whiteIcon = createIcon(Color.white);
      blackIcon = createIcon(Color.black);

      Dimension boardSize = new Dimension(600, 600);

      numSquares = 6;
      currentPlayer = true;

      layeredPane = new JLayeredPane();
      getContentPane().add(layeredPane);
      layeredPane.setPreferredSize(boardSize);
      layeredPane.addMouseListener(this);

      board = new JPanel();
      layeredPane.add(board, JLayeredPane.DEFAULT_LAYER);

      board.setLayout(new GridLayout(numSquares, numSquares));
      board.setPreferredSize(boardSize);
      board.setBounds(0, 0, boardSize.width, boardSize.height);

      for (int i = 0; i < (numSquares * numSquares); i++) {
         // !! JPanel square = new JPanel(new BorderLayout());
         JPanel square = new JPanel(new GridBagLayout()); // !!

         square.setBorder(BorderFactory.createLineBorder(Color.black));
         square.setBackground(Color.green);
         square.setName(String.format("[%d, %d]", i % numSquares, i
               / numSquares)); // !!
         board.add(square);

      }

   }

   // !!
   private ImageIcon createIcon(Color color) {
      int width = 40;
      int height = width;
      BufferedImage img = new BufferedImage(width, height,
            BufferedImage.TYPE_INT_ARGB);
      Graphics2D g2 = img.createGraphics();
      g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);
      g2.setColor(color);
      g2.fillOval(0, 0, width, height);
      g2.dispose();
      ImageIcon icon = new ImageIcon(img);
      return icon;
   }

   public static void main(String[] args) {
      JFrame frame = new Gui2();
      frame.setDefaultCloseOperation(DISPOSE_ON_CLOSE);
      frame.pack();
      frame.setResizable(true);
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   @Override
   // !!
   public void mousePressed(MouseEvent e) {
      JPanel temp = (JPanel) board.findComponentAt(e.getX(), e.getY());
      System.out.println(e.getX() + " " + e.getY());
      System.out.println(temp.getName()); // !!

      if (currentPlayer) {
         // !! ImageIcon white = new ImageIcon("l/Images/white.jpg");
         // !! piece = new JLabel(white);
         piece = new JLabel(whiteIcon); // !!
         temp.add(piece);
      } else {
         // !! ImageIcon black = new ImageIcon("/Images/black.jpg");
         // !! piece = new JLabel(black);
         piece = new JLabel(blackIcon); // !!
         temp.add(piece);
      }
      temp.revalidate(); // !!
      temp.repaint(); // !!
      currentPlayer = !currentPlayer;

   }

   @Override
   public void mouseEntered(MouseEvent e) {

   }

   @Override
   public void mouseExited(MouseEvent arg0) {
   }

   @Override
   public void mouseClicked(MouseEvent arg0) {
   }

   @Override
   public void mouseReleased(MouseEvent e) {

   }

}

Also class names should be capitalized, and also you should again make your ImageIcons once. Again, one ImageIcon can be shared by many JLabels. You'll also want to respond to mousePressed not mouseClicked as mouseClicked can be fussy, especially if you move the mouse between press down and mouse release.

Hopefully you've also seen the value of an SSCCE. :)