请求java中有关jlabel和parent的一些说明 [英] Asking for some clarification in java about jlabel and parent

问题描述

在互联网上发现这个代码，它是在几年前发布的，所以我决定在这里询问一些我不太了解的行的澄清。

Found this code in the internet, it was posted years ago, so I just decided to ask here for some clarifications for some lines I don't quite understand.

在 mousePressed 方法中，他的意思是：
chessPiece = null 他是说如果 JLabel chessPiece 中有一个图像然后应该更改为 null ？

In the mousePressed 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?

chessBoard.findComponentAt（e.getX（），e.​​getY（））返回 JPanel square？

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

最后，当组件c 获取其父级时，谁是父级？

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

整个代码如下：

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);
        }
        ....
    }

推荐答案

在 mousePiece 方法中，他的意思是： chessPiece = null 是
他说如果 JLabel chessPiece 中有图像，那么
应改为 null ？

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?

我假设你是指 mousePressed 。通过使用 chessPiece = null ，作者正在取消引用该变量，因此通过变量

I assume you mean mousePressed. By using chessPiece = null, the author is de-referencing the variable, so what ever was assigned to it is no longer reachable through the is variable

是 chessBoard.findComponentAt（e.getX（），e.​​getY（））返回 JPanel square？

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

这取决于。 findComponentAt 可以搜索当前容器及其任何子容器，直到找到指定位置的组件。 Technquial，作者忽略了触发事件的组件（应该 layeredPane ）并且正在走 chessBoard 。我怀疑他们这样做是因为如果他们使用 layeredPane ，它将返回 chessBoard 。

This depends. findComponentAt can search the current container and it's any of it's child containers until it finds a component at the specified position. Technquial, the author is ignoring the component that triggered the event (which should layeredPane) and is walking the chessBoard instead. I suspect they are doing this because if they used layeredPane it would return chessBoard instead.

该方法能够返回 JPanel ， JLabel 甚至可能 null ，但考虑到组件布局的方式，它的概率较低。

The method is capable of returning JPanel, JLabel and possibly even null, but given the way that the components are laid out, it's a lower probability.

和最后，当组件c获得其父项时，谁是父项？

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

这取决于。根据我对代码的理解，我会说它返回 JPanel 在 JLabel 片之下。

This depends. Based on my understanding of the code, I would say it's return a JPanel underneth the JLabel piece.

不得不说，虽然有更简单的方法可以达到相同的结果...

Have to say, there are easier ways to achieve the same result though...

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