java 怎么判断两条直线相交

// 判断两条直线段是否有交点，有则计算交点的坐标
// p1,p2是直线一的端点坐标
// p3,p4是直线二的端点坐标
bool detectIntersect(Point p1, Point p2, Point p3, Point p4)
{
double line_x,line_y; //交点
if ( (fabs(p1.x-p2.x)<1e-6) && (fabs(p3.x-p4.x)<1e-6) )
{
return false;
}
else if ( (fabs(p1.x-p2.x)<1e-6) ) //如果直线段p1p2垂直与y轴
{
if (between(p1.x,p3.x,p4.x))
{
double k = (p4.y-p3.y)/(p4.x-p3.x);
line_x = p1.x;
line_y = k*(line_x-p3.x)+p3.y;

if (between(line_y,p1.y,p2.y))
{
return true;
}
else
{
return false;
}
}
else
{
return false;
}
}
else if ( (fabs(p3.x-p4.x)<1e-6) ) //如果直线段p3p4垂直与y轴
{
if (between(p3.x,p1.x,p2.x))
{
double k = (p2.y-p1.y)/(p2.x-p1.x);
line_x = p3.x;
line_y = k*(line_x-p2.x)+p2.y;

if (between(line_y,p3.y,p4.y))
{
return true;
}
else
{
return false;
}
}
else
{
return false;
}
}
else
{
double k1 = (p2.y-p1.y)/(p2.x-p1.x);
double k2 = (p4.y-p3.y)/(p4.x-p3.x);

if (fabs(k1-k2)<1e-6)
{
return false;
}
else
{
line_x = ((p3.y - p1.y) - (k2*p3.x - k1*p1.x)) / (k1-k2);
line_y = k1*(line_x-p1.x)+p1.y;
}

if (between(line_x,p1.x,p2.x)&&between(line_x,p3.x,p4.x))
{
return true;
}
else
{
return false;
}
}
}

计算角度呗，算出来是0或者180不就平行了