Java编写程序，使得当按下鼠标时显示鼠标的位置。

可以使用Java Swing编写一个简单的程序实现该功能，具体代码如下：

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

public class MousePositionDemo extends JFrame implements MouseListener, MouseMotionListener {
    JLabel label;

    public MousePositionDemo() {
        super("Mouse Position Demo");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(300, 200);
        setLayout(new BorderLayout());

        label = new JLabel("Move the mouse over the window");
        add(label, BorderLayout.SOUTH);

        addMouseListener(this);
        addMouseMotionListener(this);

        setVisible(true);
    }

    public void mouseClicked(MouseEvent e) {
        // do nothing
    }

    public void mouseEntered(MouseEvent e) {
        // do nothing
    }

    public void mouseExited(MouseEvent e) {
        // do nothing
    }

    public void mousePressed(MouseEvent e) {
        Point p = e.getPoint();
        label.setText("Mouse pressed at (" + p.x + ", " + p.y + ")");
    }

    public void mouseReleased(MouseEvent e) {
        Point p = e.getPoint();
        label.setText("Mouse released at (" + p.x + ", " + p.y + ")");
    }

    public void mouseDragged(MouseEvent e) {
        // do nothing
    }

    public void mouseMoved(MouseEvent e) {
        Point p = e.getPoint();
        label.setText("Mouse moved to (" + p.x + ", " + p.y + ")");
    }

    public static void main(String[] args) {
        new MousePositionDemo();
    }
}

在该程序中，我们实现了MouseListener和MouseMotionListener接口，同时添加了鼠标事件和鼠标移动事件的监听器。当鼠标按下或释放时，会在标签上显示鼠标的位置，当鼠标移动时，标签也会实时更新鼠标的位置。