public void draw中的public为什么老是错，提示是已定义类型Square

public class Quadrangle {
private Quadrangle[] qtest = new Quadrangle[6];
private int nextIndex =0;
public void draw(
Quadrangle q){
if(nextIndex qtest[nextIndex]=q;
System.out.println(nextIndex);
nextIndex++;
}
}
public static void main(String[] args) {
Quadrangle q=new Quadrangle();
q.draw(new Parallelogramgle());
}
}
class Square extends Quadrangle{
public Square(){
System.out.println("正方形");
}
}
class Parallelogramgle extends Quadrangle{
public Parallelogramgle(){
System.out.println("平行四边形");
}
}

是否是访问说明符位置的问题？