java 画的4个点的Bezier曲线

//其中第2和第3个实心点为控制点，可以鼠标拖动，但是不能太快，不然曲线点的坐标x,y计算跟不上。

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Point2D;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class test2 extends JPanel implements MouseListener,MouseMotionListener{
	private static final long serialVersionUID = 1L;
	private Point2D[] controlPoint;
	private Ellipse2D.Double[] ellipse;
	private static final double SIDELENGTH = 8;
	private int numPoints;
	private double t=0.002;
	public test2(){
		numPoints = 0;
		controlPoint = new Point2D[4];
		ellipse = new Ellipse2D.Double[4];
		this.addMouseListener(this);
		this.addMouseMotionListener(this);
	}
	@Override
	protected void paintComponent(Graphics g) {
		// TODO Auto-generated method stub
		super.paintComponent(g);
		Graphics2D g2 = (Graphics2D)g;
		g2.setColor(Color.MAGENTA);
		for(int i=0; i<numPoints; i++) {
			if(i>0 && i<(numPoints-1)) {
				g2.fill(ellipse[i]);
			}else {
				g2.draw(ellipse[i]);
			}
			if(numPoints>1 && i<(numPoints - 1))
				g2.drawLine((int)controlPoint[i].getX(), (int)controlPoint[i].getY(), (int)controlPoint[i+1].getX(), (int)controlPoint[i+1].getY());
		}
		if(numPoints == 4) {
			double x,y;
			g2.setColor(Color.RED);
			for(double k=t; k<=1+t; k+=t) {
				x = (1-k)*(1-k)*(1-k)*controlPoint[0].getX() + 3*k*(1-k)*(1-k)*controlPoint[1].getX()
					+ 3*k*k*(1-k)*controlPoint[2].getX() + k*k*k*controlPoint[3].getX();
				y = (1-k)*(1-k)*(1-k)*controlPoint[0].getY() + 3*k*(1-k)*(1-k)*controlPoint[1].getY()
						+ 3*k*k*(1-k)*controlPoint[2].getY() + k*k*k*controlPoint[3].getY();
//				System.out.println(x + "  " + y );
				g2.drawLine((int)x, (int)y, (int)x, (int)y);
			}
		}
	}
	@Override
	public Dimension getPreferredSize() {
		// TODO Auto-generated method stub
		return new Dimension(600,600);
	}

	public static void main(String[] agrs) {
		JFrame f = new JFrame();
		test2 t2 = new test2();
		f.add(t2);
		f.pack();
		f.setVisible(true);
		f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	}
	@Override
	public void mouseClicked(MouseEvent e) {
		// TODO Auto-generated method stub
		if(numPoints <4) {
			double x = e.getX();
			double y = e.getY();
			controlPoint[numPoints] = new Point2D.Double(x, y);
			Ellipse2D.Double current = new Ellipse2D.Double(x-SIDELENGTH/2, y-SIDELENGTH/2, SIDELENGTH, SIDELENGTH);
			ellipse[numPoints] = current;
			
			numPoints++;
			repaint();
		}
	}
	@Override
	public void mousePressed(MouseEvent e) {
		// TODO Auto-generated method stub		
	}
	private int find(Point2D p){
		int flag = 5;
		for(int i=0; i<numPoints; i++) {
			if( ellipse[i].contains(p)) {
				flag = i;
				return flag;
			}
		}
		return flag;
	}
	@Override
	public void mouseReleased(MouseEvent e) {
		// TODO Auto-generated method stub	
	}
	@Override
	public void mouseEntered(MouseEvent e) {
		// TODO Auto-generated method stub	
	}
	@Override
	public void mouseExited(MouseEvent e) {
		// TODO Auto-generated method stub	
	}
	@Override
	public void mouseDragged(MouseEvent e) {
		// TODO Auto-generated method stub
		int flag  = find((Point2D)e.getPoint());
		if( flag<5) {
			double x = e.getX();
			double y = e.getY();
			controlPoint[flag] = new Point2D.Double(x, y);
			Ellipse2D.Double current = new Ellipse2D.Double(x-SIDELENGTH/2, y-SIDELENGTH/2, SIDELENGTH, SIDELENGTH);
			ellipse[flag] = current;
			
			repaint();
		}
	}
	@Override
	public void mouseMoved(MouseEvent e) {
		// TODO Auto-generated method stub		
	}	
}