java - 要求java中有关jlabel和parent的一些澄清

Question

在互联网上找到了这段代码，它是几年前发布的，所以我决定在这里要求对一些我不太理解的行进行一些澄清。

在 mousePressed方法，他的意思是: chessPiece = null他是说如果 JLabel chessPiece其中有图像，则应将其更改为 null ？

是chessBoard.findComponentAt(e.getX(), e.getY())返回 JPanel正方形？

最后，当Component c时获取其父级，谁是父级？

完整代码如下:

public class ChessGameDemo extends JFrame implements MouseListener, MouseMotionListener {

    JLayeredPane layeredPane;
    JPanel chessBoard;
    JLabel chessPiece;
    int xAdjustment;
    int yAdjustment;
    private static final String imageFolderPath = "src/resources/images/";

    public ChessGameDemo() {
        Dimension boardSize = new Dimension(600, 600);

        //  Use a Layered Pane for this this application
        layeredPane = new JLayeredPane();
        getContentPane().add(layeredPane);
        layeredPane.setPreferredSize(boardSize);
        layeredPane.addMouseListener(this);
        layeredPane.addMouseMotionListener(this);

         //Add a chess board to the Layered Pane 
        chessBoard = new JPanel();
        layeredPane.add(chessBoard, JLayeredPane.DEFAULT_LAYER);
        chessBoard.setLayout(new GridLayout(8, 8));
        chessBoard.setPreferredSize(boardSize);
        chessBoard.setBounds(0, 0, boardSize.width, boardSize.height);

        for (int i = 0; i < 64; i++) {
            JPanel square = new JPanel(new BorderLayout());
            chessBoard.add(square);

            int row = (i / 8) % 2;
            if (row == 0) {
                square.setBackground(i % 2 == 0 ? Color.blue : Color.white);
            } else {
                square.setBackground(i % 2 == 0 ? Color.white : Color.blue);
            }
        }

          //Add a few pieces to the board
        JLabel piece = new JLabel(new ImageIcon(imageFolderPath + "/pieces/bdg.png"));
        JPanel panel = (JPanel) chessBoard.getComponent(0);
        panel.add(piece);
        piece = new JLabel(new ImageIcon(imageFolderPath + "/pieces/belder.png"));
        panel = (JPanel) chessBoard.getComponent(15);
        panel.add(piece);
        piece = new JLabel(new ImageIcon(imageFolderPath + "/pieces/bhero.png"));
        panel = (JPanel) chessBoard.getComponent(16);
        panel.add(piece);
        piece = new JLabel(new ImageIcon(imageFolderPath + "/pieces/borb.png"));
        panel = (JPanel) chessBoard.getComponent(20);
        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);
        chessPiece.setSize(chessPiece.getWidth(), chessPiece.getHeight());
        layeredPane.add(chessPiece, JLayeredPane.DRAG_LAYER);
    }

        //Move the chess piece around
    public void mouseDragged(MouseEvent me) {
        if (chessPiece == null) {
            return;
        }
        chessPiece.setLocation(me.getX() + xAdjustment, me.getY() + yAdjustment);
    }

         //Drop the chess piece back onto the chess board
    public void mouseReleased(MouseEvent e) {
        if (chessPiece == null) {
            return;
        }

        chessPiece.setVisible(false);
        Component c = chessBoard.findComponentAt(e.getX(), e.getY());

        if (c instanceof JLabel) {
            Container parent = c.getParent();
            parent.remove(0);
            parent.add(chessPiece);
        } else {
            Container parent = (Container) c;
            parent.add(chessPiece);
        }
        ....
    }

Answer 1

In the mousePiece method, what does he mean by: chessPiece = null is he saying that if the JLabel chessPiece has a image in it then it should be changed to null?

我假设您的意思是mousePressed。通过使用 chessPiece = null，作者取消了对变量的引用，因此分配给它的内容不再可以通过 is 变量访问

Is chessBoard.findComponentAt(e.getX(), e.getY()) returns the JPanel square?

这要看情况。 findComponentAt 可以搜索当前容器及其任何子容器，直到在指定位置找到组件。从技术上讲，作者忽略了触发事件的组件(应该是 layeredPane)，而是在 chessBoard 上行走。我怀疑他们这样做是因为如果他们使用layeredPane，它将返回chessBoard。

该方法能够返回 JPanel、JLabel 甚至可能返回 null，但考虑到组件的布局方式，它是概率较低。

and lastly, when Component c gets its parent, who is the parent?

这要看情况。根据我对代码的理解，我会说它在 JLabel 部分下面返回一个 JPanel 。

不得不说，有更简单的方法可以达到相同的结果......