android画布绘制线条与指针结束箭头两侧。有人能帮我解决这个问题吗？

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    // 绘制线条
    Paint linePaint = new Paint();
    linePaint.setColor(Color.BLACK);
    linePaint.setStrokeWidth(5);
    canvas.drawLine(100, 100, 300, 100, linePaint);

    // 绘制指针
    Paint pointerPaint = new Paint();
    pointerPaint.setColor(Color.RED);
    pointerPaint.setStrokeWidth(5);
    pointerPaint.setStyle(Paint.Style.FILL);
    Path pointerPath = new Path();
    pointerPath.moveTo(300, 100);
    pointerPath.lineTo(280, 90); // 箭头左侧点
    pointerPath.lineTo(280, 110); // 箭头右侧点
    pointerPath.close();
    canvas.drawPath(pointerPath, pointerPaint);
}