Hello bulimic, i think that circulo is not a inner class of cilindro. I think that circulo is a subclass of cilindro. I send a copy of how i do it. Please see it and tell me if is correct. > Date: Mon, 30 Mar 2009 11:53:33 -0700 > Subject: [java programming] Re: Logic error! > From: [email protected] > To: [email protected] > > > On Mar 31, 1:36 am, jose luis garcia <[email protected]> wrote: > > *Hello everybody... I have a problem. I wrote a code for a program that have > > 1 superclass and 1 class extends. the code it`s follow:* > > > > //Programa que realiza algunos calculos mediante las caracteristicas de un > > cilindro > > > > package cilindro; > > > > // @author louis > > > > import java.util.Scanner; > > > > public class Cilindro { > > double pi = Math.PI; > > > > public Cilindro(){ > > // super(); > > > > } > > > > public double areaCilindro(double r, double h){ > > double area = (2*pi*r*h) + (2*pi*r*r); > > > > return area; > > } > > > > public double perimetroCilindro(double r, double h){ > > double perimetro = (4*pi*r)+(2*h); > > > > return perimetro; > > > > } > > > > public class Circulo extends Cilindro{ > > > > Circulo(){ > > super(); > > } > > > > public double areaCirculo(double r){ > > > > double area = pi*r*r; > > return area; > > } > > > > public double perimetroCirculo(double r){ > > double perimetro = 2*pi*r; > > > > return r; > > } > > > > } > > > > public static void main(String[] args) { > > > > // Cilindro obj = null; > > Circulo obj1 = null; > I suspect the culprit is the inner class. If I remember correctly, an > inner class type declaration should be like: > Cilindro.Circulo obj1 = null; > > > double radio = 0,altura = 0; > > Scanner input = new Scanner(System.in); > > > > System.out.println("Ingresa Radio: "); > > radio = input.nextFloat(); > > > > /* System.out.println("Ingresa altura: "); > > altura = input.nextFloat(); > > */ > > String resultado = "Area del circulo: " + > > obj1.areaCirculo(radio); > > > > System.out.println(resultado); > > > > } > > > > } > > > > *Netbeans not generate any error. But at the moment that run the program and > > insert a float, Netbeans generate me this message:* > > > > run: > > Ingresa Radio: > > Exception in thread "main" java.lang.NullPointerException > > at cilindro.Cilindro.main(Cilindro.java:66) > > 2.23 > > Java Result: 1 > > GENERACIÓN CORRECTA (tiempo total: 3 segundos) > > > > * > > I`m sure that is a logic error... help me please. Thanks! > > * > > >
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