我尝试扩展JPanel，但在菜单下有一个10x10 pix灰色小框。至少开始
使用JComponent时，首选大小为（0，0），这就是为什么什么都看不到的原因。
当您使用JPanel时，默认情况下使用FlowLayout，并且在将每个组件添加到面板之前/之后，FlowLayout的间隙为5像素。由于您没有添加任何组件，因此首选大小仅是间隙，因此您获得的大小为（10，10）。
因此，在进行自定义绘画时，您需要重写getPreferredSize（）方法，以为要实现的自定义绘画返回适当的值。
编辑：
import java.awt.*;import java.awt.event.*;import java.util.*;import javax.swing.*;public class ChessBoard extends Jframe implements MouseListener, MouseMotionListener{ JLayeredPane layeredPane; JPanel chessBoard; JLabel chessPiece; int xAdjustment; int yAdjustment; public ChessBoard() { Dimension boardSize = new Dimension(600, 600); // Use a Layered Pane for this this application layeredPane = new JLayeredPane(); layeredPane.setPreferredSize( boardSize ); layeredPane.addMouseListener( this ); layeredPane.addMouseMotionListener( this ); getContentPane().add(layeredPane); // Add a chess board to the Layered Pane chessBoard = new JPanel(); chessBoard.setLayout( new GridLayout(8, 8) ); chessBoard.setPreferredSize( boardSize ); chessBoard.setBounds(0, 0, boardSize.width, boardSize.height); layeredPane.add(chessBoard, JLayeredPane.DEFAULT_LAYER); // Build the Chess Board squares for (int i = 0; i < 8; i++) { for (int j = 0; j < 8; j++) { JPanel square = new JPanel( new BorderLayout() ); square.setBackground( (i + j) % 2 == 0 ? Color.red : Color.white ); chessBoard.add( square ); } } // Add a few pieces to the board ImageIcon duke = new ImageIcon("dukewavered.gif"); // add an image here JLabel piece = new JLabel( duke ); JPanel panel = (JPanel)chessBoard.getComponent( 0 ); panel.add( piece ); piece = new JLabel( duke ); panel = (JPanel)chessBoard.getComponent( 15 ); panel.add( piece ); } public void mousePressed(MouseEvent e) { chessPiece = null; Component c = chessBoard.findComponentAt(e.getX(), e.getY()); if (c instanceof JPanel) return; Point parentLocation = c.getParent().getLocation(); xAdjustment = parentLocation.x - e.getX(); yAdjustment = parentLocation.y - e.getY(); chessPiece = (JLabel)c; chessPiece.setLocation(e.getX() + xAdjustment, e.getY() + yAdjustment); layeredPane.add(chessPiece, JLayeredPane.DRAG_LAYER); layeredPane.setCursor(Cursor.getPredefinedCursor(Cursor.MOVE_CURSOR)); } public void mouseDragged(MouseEvent me) { if (chessPiece == null) return; // The drag location should be within the bounds of the chess board int x = me.getX() + xAdjustment; int xMax = layeredPane.getWidth() - chessPiece.getWidth(); x = Math.min(x, xMax); x = Math.max(x, 0); int y = me.getY() + yAdjustment; int yMax = layeredPane.getHeight() - chessPiece.getHeight(); y = Math.min(y, yMax); y = Math.max(y, 0); chessPiece.setLocation(x, y); } public void mouseReleased(MouseEvent e) { layeredPane.setCursor(null); if (chessPiece == null) return; // Make sure the chess piece is no longer painted on the layered pane chessPiece.setVisible(false); layeredPane.remove(chessPiece); chessPiece.setVisible(true); // The drop location should be within the bounds of the chess board int xMax = layeredPane.getWidth() - chessPiece.getWidth(); int x = Math.min(e.getX(), xMax); x = Math.max(x, 0); int yMax = layeredPane.getHeight() - chessPiece.getHeight(); int y = Math.min(e.getY(), yMax); y = Math.max(y, 0); Component c = chessBoard.findComponentAt(x, y); if (c instanceof JLabel) { Container parent = c.getParent(); parent.remove(0); parent.add( chessPiece ); parent.validate(); } else { Container parent = (Container)c; parent.add( chessPiece ); parent.validate(); } } public void mouseClicked(MouseEvent e) {} public void mouseMoved(MouseEvent e) {} public void mouseEntered(MouseEvent e) {} public void mouseExited(MouseEvent e) {} public static void main(String[] args) { Jframe frame = new ChessBoard(); frame.setDefaultCloseOperation( DISPOSE_ON_CLOSE ); frame.setResizable( false ); frame.pack(); frame.setLocationRelativeTo( null ); frame.setVisible(true); }}
