将扫描仪的下一个字符串转换为Int并检查输入的文本是否为数字

Question

I am trying to Convert Scanner next string to Int and check that the text entered is a number, if not number system print this is not a number but if number it is converted to int and divided by ten.

If i dont check for the condition in the code, the code is running as it is supposed to. But if text is entered it is calculating the charachters index value.

If the condition is there then it is making calculation for each number instead of suming up the number Before making the calculation, but it dont calculate other charachters index value.

Without checking for the condition:

    Scanner inputtext = new Scanner(System.in); 

    System.out.print("Mata in ett tal: ");
    String number =    inputtext.next();  //Här matar användaren in text.              
    int sum = 0;
    double number2 = 10.0;

    for (int i=0; i < number.length(); i++) { //Här omvandlas texten till tal.

    sum *= 10;
    sum += (int) number.charAt(i)-(int)'0'; 
    }   

    System.out.println("Resultat: " + sum); //Här matas talet ut.
    System.out.println("Resultat delat med 10 : " + (sum/number2)); //Här divideras talet med 10.


  }

}

When checking:

    Scanner inputtext = new Scanner(System.in); 

    System.out.print("Mata in ett tal: ");
    String number =    inputtext.next();  //Här matar användaren in text.              
    int sum = 0;
    double number2 = 10.0;

    for (int i=0; i < number.length(); i++) { //Här omvandlas texten till tal.
    char ch = number.charAt(i);

    if (ch == '0' || ch == '1' || ch == '2' || ch == '3' || ch == '4' ||  ch == '5' || ch == '6'|| ch == '7'|| ch == '8'|| ch == '9'){ 
    sum *= 10;
    sum += (int) number.charAt(i)-(int)'0';

    } else { 
    System.out.println("Detta är inte ett tal");
    break; 
    }
    System.out.println("Resultat: " + sum); //Här matas talet ut.
    System.out.println("Resultat delat med 10 : " + (sum/number2)); //Här divideras talet med 10.            
   }

}

}

I expect that if a string is entered containing numbers then the calculation is performed, if other charachters are added then the user is told that this is not a number

Answer 1

You can use methods from Character which are :

• Character.isDigit
• Character.isLetter
• Character.isLetterOrDigit

By using this, iterate over the string and test if all characters are number or not.

Answer 2

Also, remember that "//d" stands for a digit so if you want it to scan for a digit only you can use that. I know this doesn't really explain too much but I thought a reminder might help.