如何确保用户输入仅是整数？

Question

I did everything as far as concepts. I made my class, and my client class. The assignment is to make a program that allows the user to input 10 grades into a gradebook, and get the max, min, and average grade of class.

My only problem is I want to make sure the user cannot put anything in the program that is not an integer; do I put instructions like that in my class or client java doc?

This is my class:

import java.util.Arrays;

public class ExamBook{

   int grades[];
   int classSize;
   int MIN = 0;
   int MAX = 100;

   public ExamBook(int[] gradeBook)
   {
      classSize = 10;
   //instantiate array with same length as parameter
      grades = new int[gradeBook.length];

      for ( int i = 0; i <= gradeBook.length-1; i++ )
      {
         grades[i] = gradeBook[i];
      }
      Arrays.sort(grades);
   }

   //setter, or mutator
   public void setClassSize( int newClass )
   {
      classSize = newClass;
   }

   //get return method
   public int getClassSize()
   {
      return classSize;
   }

   //calculate highest grade
   public int calculateMaxGrade()
   {
      int max = grades[0]; //assuming that the first index is the highest grade

       for ( int i = 0; i <= grades.length - 1; i++ )
      {
         if ( grades[i] > max )
            max = grades[i]; //save the new maximum
      }
      return max;
   }

   //calculate lowest grade
   public int calculateMinGrade()
   {
      int min = grades[0]; //assuming that the first element is the lowest grade

      for ( int i = 0; i <= grades.length - 1; i++ )
      {
         if ( grades[i] < min)
            min = grades[i]; //save the new minimum
      }
      return min;
   }

  //calculate average
   public double calculateAverageGrades()
   { 
      double total = 0;
      double average = 0;

      for ( int i = 0; i < grades.length; i++ )
      { 
         total += grades[i];
      }
       average = total/grades.length;
       return average;
   }

  //return an assorted array
   public int[] assortedGrades()
   {
      Arrays.sort(grades);
      return grades;
   }

   //return printable version of grades
   @Override
   public String toString()
   {

      String returnString = "The assorted grades of the class in ascending order is this: " + "\t";
      for ( int i = 0; i <= grades.length - 1; i++ )
      {
         returnString += grades[i] + "\t";
      }

      returnString += " \nThe class average is a/an " + calculateAverageGrades() + "." + "\nThe highest grade in the class is " + calculateMaxGrade() + "." + "\nThe lowest grade in the class is " + calculateMinGrade() + ".";

      returnString += "\n";

      return returnString;
   }



}




 **This is my client:**     


import java.util.Scanner; 
import java.util.Arrays;

public class ExamBookClient
{
   public static ExamBook classRoom1;
   public static void main( String[] args)
   {
       int MAX = 100;
       int MIN = 0;

       Scanner scan = new Scanner(System.in);
       //create array for testing class 
       int[] grading = new int [10];
       System.out.println("Please enter 10 grades to go into the exam book.");
       if(scan.hasNextInt())
       {
         for (int i = 0; i < grading.length; i++)
          {
             int x = scan.nextInt();
             if( x>MIN && x<MAX)
             {
                 grading[i] = x;
             }
          }
       }

       classRoom1 = new ExamBook (grading);
       System.out.println("The classroom size is " + classRoom1.getClassSize() + "." 
            + "\n" + classRoom1.toString() + ".");

      }
  }

Answer 1

You might want to do this in two parts - your API should specify that it works with only integers - perhaps the method which processes the grades will accept Integer arguments only. The parser of the String can specify in its Javadocs what it does when the argument passed to it is not an integer. You client should also validate that the input is an integer (maybe within the valid range). If the user input is incorrect, then maybe it can display a usage manual.

Answer 2

You can check using the below code. If you pass other than number it would throw NumberFormatException

            public static boolean checkIfNumber(String input) {
                try {
                    Integer in = new Integer(input);
                } catch (NumberFormatException e) {
                    return false;
                }
                return true;
            }

Answer 3

You can change this part as follows. This way the user can enter non-integers but in those cases you will print out warnings and you will ignore them.

    System.out.println("Please enter 10 grades to go into the exam book.");
    int i = 0;
    int x = -1;
    while (scan.hasNext() && i < 9) {
        String sx = scan.next();
        try {
            x = Integer.parseInt(sx);
            i++;
            if (x > MIN && x < MAX) {
                grading[i] = x;
            }
        } catch (NumberFormatException e) {
            System.out.println("Not an integer.");
        }
    }

    classRoom1 = new ExamBook(grading);

Answer 4

Prompt for scan.hasNextInt() in your for loop of your client instead of outside the for loop. Like this:

boolean failed = false;
for (int i = 0; i < grading.length; i++)
      {
         if (failed)
             scan.nextLine();

         failed = false;

         if (scan.hasNextInt()) {

             int x = scan.nextInt();
             if(x >= MIN && x <= MAX)
             {
             grading[i] = x;
             } else {
             System.out.println("Grade must be from 0-100!");
             i--;
             continue;
             }

         } else {
          // jump back to the start of this iteration of the loop and re-prompt
          i--;
          System.out.println("Number must be an int!");
          failed = true;
          continue;
         }
      }

Answer 5

Chech this link , it has the solution.

You must use the method hasNextInt() of Scanner .

Answer 6

If you do not want to use exceptions you can always use a Regex match to check that what you have in the string is a number valid for you.

Bearing in mind that your valid numbers are between 0 and 100, and 0 and 100 are not included seeing you code, the reg ex will be:

s.matches("[1-9][0-9]{0,1}")

Basically what this means is that you are going to have a character that is a number between 1 and 9 as first char, and then you could have one between 0 and 9, this way you do not allow 0 at the beginning (01 is not valid) and 0 by it self is also not valid. 100 has 3 chars so is not valid neither.