RETORNO DE VALORES COM FUNÇÕES

class Retangulo{
    public int width, height;

    public int areaTotal(){
        return width * height;
    }
    public boolean isQuadrado(){
        if(width==height)
            return true;
        return false;
    }
}

public class Main {

    public static void main(String args[]) {

        Retangulo r1=null;
        if(r1!=null)
            r1.isQuadrado();
        //NullPointerException
    }

}