要實現鼠標拖動畫矩形，可以使用Java的Swing庫來完成。下面是一個簡單的示例代碼：

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

public class DraggableRectangle extends JFrame {
    private int initialX, initialY;
    private int currentX, currentY;
    private Rectangle rectangle;

    public DraggableRectangle() {
        setTitle("Draggable Rectangle");
        setSize(400, 400);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // 創建矩形并設置初始位置和大小
        rectangle = new Rectangle(100, 100, 100, 100);

        // 添加鼠標事件監聽器
        addMouseListener(new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent e) {
                // 記錄鼠標按下時的初始位置
                initialX = e.getX();
                initialY = e.getY();
            }
        });

        addMouseMotionListener(new MouseAdapter() {
            @Override
            public void mouseDragged(MouseEvent e) {
                // 計算鼠標拖動后的位置
                currentX = e.getX();
                currentY = e.getY();

                // 計算矩形的偏移量
                int offsetX = currentX - initialX;
                int offsetY = currentY - initialY;

                // 更新矩形的位置
                rectangle.setLocation(rectangle.x + offsetX, rectangle.y + offsetY);

                // 重繪窗口
                repaint();

                // 更新初始位置
                initialX = currentX;
                initialY = currentY;
            }
        });
    }

    @Override
    public void paint(Graphics g) {
        super.paint(g);

        // 繪制矩形
        g.fillRect(rectangle.x, rectangle.y, rectangle.width, rectangle.height);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            DraggableRectangle draggableRectangle = new DraggableRectangle();
            draggableRectangle.setVisible(true);
        });
    }
}

運行以上代碼，將會顯示一個可拖動的矩形窗口。當鼠標按下并拖動時，矩形會跟隨鼠標的移動而移動。