java计算两条线段交点

1、判断斜率相同不，y2-y1/x2-x1,y4-y3/x4-x3,相同则无交点，不相同说明直线有交点则执行第二步； 
   2、设y=ax+b,通过斜率可求出a的值，通过坐标可以求出b的值，这样两个线段所在直线的两个方程式就得到了； 

   3、通过两个方程式求出交点，再判断交点是不是落在两线段交点的区域中

 

代码：

public  static Point getCrossPoint(Lseg lsegA,Lseg lsegB){
        float x;
        float y;
        float x1=lsegA.getA().getX();
        float y1=lsegA.getA().getY();
        float x2=lsegA.getB().getX();
        float y2=lsegA.getB().getY();
        float x3=lsegB.getA().getX();
        float y3=lsegB.getA().getY();
        float x4=lsegB.getB().getX();
        float y4=lsegB.getB().getY();
        float k1=Float.MAX_VALUE;
        float k2=Float.MAX_VALUE;
        boolean flag1=false;
        boolean flag2=false;
        
        if((x1-x2)==0)
            flag1=true;
        if((x3-x4)==0)
            flag2=true;
        
        if(!flag1)
            k1=(y1-y2)/(x1-x2);
        if(!flag2)
            k2=(y3-y4)/(x3-x4);
        
        if(k1==k2)
            return null;
        
        if(flag1){
            if(flag2)
                return null;
            x=x1;
            if(k2==0){
                y=y3;
            }else{
                y=k2*(x-x4)+y4;
            }
        }else if(flag2){
            x=x3;
            if(k1==0){
                y=y1;
            }else{
                y=k1*(x-x2)+y2;
            }
        }else{
            if(k1==0){
                y=y1;
                x=(y-y4)/k2+x4;
            }else if(k2==0){
                y=y3;
                x=(y-y2)/k1+x2;
            }else{
                x=(k1*x2-k2*x4+y4-y2)/(k1-k2);
                y=k1*(x-x2)+y2;
            }            
        }
        if(between(x1,x2,x)&&between(y1,y2,y)&&between(x3,x4,x)&&between(y3,y4,y)){
            Point point=new Point();
            point.setX(x);
            point.setY(y);
            if(point.equals(lsegA.getA())||point.equals(lsegA.getB()))
                return null;
            return point;
        }else{
            return null;
        }                
    }
    
    public static boolean between(float a,float b,float target){
        if(target>=a-0.01&&target<=b+0.01||target<=a+0.01&&target>=b-0.01)
            return true;
        else
            return false;
    }}