I started studying Object Orientation and decided to make a simple calculator program. At the moment I just made the sum to see if the way I was doing is right.
Follow the code:
package javaapplication100;
import java.util.Scanner;
/**
*
* @author Marcielli
*/
public class JavaApplication100 {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
Calculadora calc = new Calculadora();
System.out.println("Digite:\n+ - Somar\n* - Multiplicar\n/ - Dividir\n- - Subtrair");
String escolha = input.nextLine();
switch (escolha) {
case "+":
System.out.println("Somar quantos numeros? ");
int a = input.nextInt();
calc.setNumerosSomar(a);//Esta acusando erro aqui.
//calc.setNumerosSomar(calc.qntNumeros = input.nextInt());
System.out.println("A soma: "+calc.getNumerosSomar());
break;
case "*":
break;
case "/":
break;
case "-":
break;
default:
break;
}
}
}
class Calculadora {
Scanner input = new Scanner(System.in);
protected double[] numerosSomar;
private double[] numerosMultiplicar;
private double[] numerosDividir;
private double[] numerosSubtrair;
public int qntNumeros;
public double resSoma;
public double resMultiplicar;
public double resDividir;
public double resSubtrair;
public void setNumerosSomar(int a) {
this.qntNumeros = a;
for(int i=0; i<qntNumeros; i++) {
System.out.println("Digite um numero: ");
numerosSomar[i] = input.nextDouble(); //Esta acusando erro aqui.
}
for(int i=0; i<qntNumeros; i++) {
resSoma+=numerosSomar[i];
}
}
public double getNumerosSomar() {
return resSoma;
}
}
I'm really not sure if I'm doing anything right because I'm still trying to understand the concept of Object Guidance as a whole.
The problem I'm having is the error:
Exception in thread "main" java.lang.NullPointerException.
I left a comment on the lines that IDE is pointing out that it is in trouble. But by the way of doubts follow them below:
calc.setNumerosSomar(a);
numerosSomar[i] = input.nextDouble();
My question here is this, is it a logic error? Because I believe the problem is not in the method, because if I typed 2 into qntNumeros (variable used to determine when it will stop), that variable will be worth 2 .
The for loop is 0 < qntNumeros(que vale 2) . Here seems to me no mistake at all.
I also do not see error in line numerosSomar[i] = input.nextDouble(); , because I really believe this is how you save a value in a double-type vector.
Looking at this question Exception in thread "main" java.lang. NullPointerException I believe I am trying to write data to a null state, and that I need to initialize the vector before. But I did not understand how I should initialize the vector before.