画带箭头的直线

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

import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.geom.*;

public class DrawFrame extends JFrame {
    /**
     *
     */
    private static final long serialVersionUID = 1L;
    // 活动图窗口大小
    public static final int DEFAULT_WIDTH = 1000;
    public static final int DEFAULT_HEIGHT = 800;
    public DrawFrame() {
        setTitle("Activity Diagram");
        setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
        ArrowLinePanel panel = new ArrowLinePanel();
        add(panel);
    }

    public static void main(String args[]) {
        DrawFrame frame = new DrawFrame();
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.setVisible(true);
    }

}

class ArrowLinePanel extends JPanel implements MouseMotionListener,MouseListener{
    // confirm the line position
  private int x1 = 0;
  private int y1 = 0;
  private int x2 = 0;
  private int y2 = 0;

    public ArrowLinePanel() {
        setBackground(Color.white);
        addMouseListener(this);
        addMouseMotionListener(this);
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        g2.setPaint(Color.black);
        drawAL(x1, y1, x2, y2, g2);// 这里x1, y1, x2, y2必须要声明并且初始化，而具体声明的位置和初始化的值
    }

    public static void drawAL(int sx, int sy, int ex, int ey, Graphics2D g2)
    {
        double H = 10; // 箭头高度
        double L = 4; // 底边的一半
        int x3 = 0;
        int y3 = 0;
        int x4 = 0;
        int y4 = 0;
        double awrad = Math.atan(L / H); // 箭头角度
        double arraow_len = Math.sqrt(L * L + H * H); // 箭头的长度
        double[] arrXY_1 = rotateVec(ex - sx, ey - sy, awrad, true, arraow_len);
        double[] arrXY_2 = rotateVec(ex - sx, ey - sy, -awrad, true, arraow_len);
        double x_3 = ex - arrXY_1[0]; // (x3,y3)是第一端点
        double y_3 = ey - arrXY_1[1];
        double x_4 = ex - arrXY_2[0]; // (x4,y4)是第二端点
        double y_4 = ey - arrXY_2[1];

        Double X3 = new Double(x_3);
        x3 = X3.intValue();
        Double Y3 = new Double(y_3);
        y3 = Y3.intValue();
        Double X4 = new Double(x_4);
        x4 = X4.intValue();
        Double Y4 = new Double(y_4);
        y4 = Y4.intValue();
        // 画线
        g2.drawLine(sx, sy, ex, ey);
        //
        GeneralPath triangle = new GeneralPath();
        triangle.moveTo(ex, ey);
        triangle.lineTo(x3, y3);
        triangle.lineTo(x4, y4);
        triangle.closePath();
        //实心箭头
        g2.fill(triangle);
        //非实心箭头
        //g2.draw(triangle);

    }

    // 计算
    public static double[] rotateVec(int px, int py, double ang,
            boolean isChLen, double newLen) {

        double mathstr[] = new double[2];
        // 矢量旋转函数，参数含义分别是x分量、y分量、旋转角、是否改变长度、新长度
        double vx = px * Math.cos(ang) - py * Math.sin(ang);
        double vy = px * Math.sin(ang) + py * Math.cos(ang);
        if (isChLen) {
            double d = Math.sqrt(vx * vx + vy * vy);
            vx = vx / d * newLen;
            vy = vy / d * newLen;
            mathstr[0] = vx;
            mathstr[1] = vy;
        }
        return mathstr;
    }

    @Override
    public void mouseDragged(MouseEvent e) {
                 //改变箭头的坐标
        x2 = e.getX();
        y2 = e.getY();
        repaint();
    }

    @Override
    public void mouseMoved(MouseEvent e) {
    }

    @Override
    public void mouseClicked(MouseEvent e) {
    }

    @Override
    public void mouseEntered(MouseEvent e) {
    }

    @Override
    public void mouseExited(MouseEvent e) {
    }

    @Override
    public void mousePressed(MouseEvent e) {
                //设置箭头的起始坐标
        x1 = e.getX();
        y1 = e.getY();
    }

    @Override
    public void mouseReleased(MouseEvent e) {

    }

}