Error control, it generates infinite loop

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Error control, it generates infinite loop

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#1 by (3 votes)
#2 by (2 votes)

1

I am starting to use try-catch . In this example I ask for a number and if the user enters a number it is displayed, if he writes any letter the error jumps.

My intention was that when I entered a letter I would miss the message of "Lo siento, has introducido letras" , and that I would ask for the number again. The problem is that it shows me the message of "Lo siento..." infinitely.

/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
    int num;
    boolean error;

    Scanner pedir = new Scanner(System.in);
    do {
        try {
            System.out.print("Inserte un numero: ");
            num = pedir.nextInt();
            System.out.println("El valor es " + num);
            error=false;
        } catch (InputMismatchException e) {
            error=true;
            System.out.println("Lo siento has introducido letras ");
        }
    }while(error);

}

java

asked by AnnaPS 18.01.2017 в 12:52

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2 answers

3

You just have to add pedir.next() in error handling:

public static void main(String[] args) {
    int num;
    boolean error;

    Scanner pedir = new Scanner(System.in);
    do {
        try {
            System.out.print("Inserte un numero: ");
            num = pedir.nextInt();
            System.out.println("El valor es " + num);
            error=false;
        } catch (InputMismatchException e) {
            error=true;
            System.out.println("Lo siento has introducido letras ");
            pedir.next();
        }
    }while(error);

}

answered by 18.01.2017 в 13:15

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score 2 · Accepted Answer

You are not cleaning the incorrectly entered number, so you will always try again to get what you entered the first time.

To clean the invalid data you must read a complete line:

public static void main(String[] args) {
  int num;

  Scanner pedir = new Scanner(System.in);
  while (true) {
    System.out.print("Inserte un numero: ");
    try {
      num = pedir.nextInt();
      System.out.println("El valor es " + num);
      break;
    } catch (InputMismatchException e) {
      /* Limpiamos la entrada incorrecta */
      pedir.next();
      System.out.println("Lo siento, has introducido letras");
    } catch (NoSuchElementException e) {
      /* Nunca se captura, ver:
      https://docs.oracle.com/javase/7/docs/api/java/lang/RuntimeException.html */
      System.out.println("Fin de la entrada de datos");
      break;
    }
  }
}

That should be enough, but keep in mind that you should check if the field with hasNextInt() is valid instead of try/catch :

public static void main(String[] args) {
  int num;

  Scanner pedir = new Scanner(System.in);
  while (true) {
    System.out.print("Inserte un numero: ");
    /* Comprobamos si quedan más datos en la entrada estándar */
    if (pedir.hasNext()) {
      if (pedir.hasNextInt()) {
        num = pedir.nextInt();
        System.out.println("El valor es " + num);
        break;
      } else {
        /* Limpiamos la entrada incorrecta */
        pedir.next();
        System.out.println("Lo siento, has introducido letras");
      }
    } else {
      System.out.println("Fin de la entrada de datos");
      break;
    }
  }
}