java求三个点组成的三角形面积

class Point{
private double x,y;
public Point(){
x=0;y=0;
}
public Point(double x,double y){
this.x=x;this.y=y;
}
public double getX(){
return x;
}
public double getY(){
return y;
}
}

class Triangle{
private Point p1,p2,p3;
public Triangle(){
p1=new Point();
p2=new Point();
p3=new Point();
}
public Triangle(double x1,double y1,double x2,double y2,double x3,double y3){
p1=new Point(x1,y1);
p2=new Point(x2,y2);
p3=new Point(x3,y3);
}
public double getArea(){
double x1=p1.getX(),y1=p1.getY(),x2=p2.getX(),y2=p2.getY(),x3=p3.getX(),y3=p3.getY();
double s1=Math.sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
double s2=Math.sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3));
double s3=Math.sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3));
double p=(s1+s2+s3)/2;
double a=Math.sqrt(p*(p-a)*(p-b)*(p-c));
return a;
}
}

应该是这样。