Checking input type...how?

Question

I have the following method:

public void addStudent(){

    String fName, lName;
    double mGrade, fGrade;
    System.out.print("\nEnter first name: ");
    Scanner in = new Scanner(System.in);
    fName = in.nextLine();
    System.out.print("\nEnter last name: ");
    lName = in.nextLine();
    System.out.print("\nEnter midterm grade: ");
    mGrade = in.nextDouble();
    System.out.print("\nEnter final grade: ");
    fGrade = in.nextDouble();
    Student toAdd = new Student(fName, lName, mGrade, fGrade);
    students.add(toAdd);
    System.out.println("\nStudent record added.\n");
    System.out.println(students.size());
}

How can I check if the user typed in something other than an integer for midterm grade and final grade? And if they entered a non-integer, I want the method to just request the user type in that value again. I'm guessing I'll have to use a do-while loop. But I don't don't know how to check the type...

Thanks!

possible duplicate of What's the best way to check to see if a String represents an integer in Java? — Mike Samuel
– Mike Samuel, Commented Mar 16, 2011 at 23:42
@mike - thanks, that might help. i'm not allowed to add methods for this problem though. — user618712
– user618712, Commented Mar 16, 2011 at 23:46

Argote · Accepted Answer · 2011-03-16 23:41:09Z

2

You can use Scanner.next() and try to parse it to the type you want (ex. to integer by using Integer.parseInt(x) and if it fails (throws and exception) try to do it again.

answered Mar 16, 2011 at 23:41

Argote

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2 Comments

user618712 Over a year ago

er, i messed up in my original post. can i parse a double?

Argote Over a year ago

Yes you can, you can do that by using Double.parseDouble(x)

Richard J. Ross III · Accepted Answer · 2011-03-17 01:08:26Z

1

Yes, a do-while will work best.

  int midterm;
  System.out.printLn("Enter midterm grade");
  do
  { 
      try {
          string s = in.nextLine();
          midterm = Integer.parseInt(s);
          break;
      }
      catch (Exception e)
      {
          System.out.printLn("Couldn't parse input, please try again");
      }
  }
  while (true);

edited Mar 17, 2011 at 1:08

answered Mar 16, 2011 at 23:45

Richard J. Ross III

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2 Comments

user618712 Over a year ago

er, i messed up in my description...can i parse a double?

Richard J. Ross III Over a year ago

Absolutely, instead of integer, use Double.parse.

OscarRyz · Accepted Answer · 2011-03-16 23:40:47Z

1

You may use the method: nextInt() from Scanner

Alternatively you can check if a string is an integer like this:

if( someString.matches("\\d+") ) {
  // it is 
} else {
 // it isn't 
}

answered Mar 16, 2011 at 23:40

OscarRyz

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1 Comment

Jae Carr Over a year ago

Thanks, this works beautifully for a similar issue I was having. I much prefer this to making a try/catch block.

Dheeraj Joshi · Accepted Answer · 2011-03-17 04:11:11Z

1

Run the input method in a loop, if user enters something other than valid integer or double, repeat asking for the input.

answered Mar 17, 2011 at 4:11

Dheeraj Joshi

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Comments

Nischay Sinha · Accepted Answer · 2016-10-15 18:32:50Z

you can try this

import java.io.*;
import java.util.Scanner;
public class Test {
    public static void main(String args[]) throws Exception {

        String input;
        int ch1;
        float ch2;
        String ch3;

        Scanner one = new Scanner(System.in);

        input = one.nextLine();

        try {
            ch1 = Integer.parseInt(input);
            System.out.println("integer");
            return;
        } catch (NumberFormatException e) {


        }

        try {
            ch2 = Float.parseFloat(input);
            System.out.println("float");
            return;
        } catch (NumberFormatException e) {

        }
        try {
            ch3 = String.valueOf(input);
            System.out.println("String");
        } catch (NumberFormatException e) {

        }


    }
}

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