Question

So, I was looking for an efficient way, using Java’s standard packages, to read an input integer… For example, I came across the class “Scanner”, but I found two main difficulties:

1. if I don’t insert an int, I’m not actually able to solve the exception;
2. this class works with tokens, but my aim is to load the string in its full length.

This is an example of execution I would like to realize:

Integer: eight
Input error - Invalid value for an int.
Reinsert: 8 secondtoken
Input error - Invalid value for an int.
Reinsert: 8
8 + 7 = 15

And this is the (incorrect) code I tried to implement:

import java.util.Scanner;
import java.util.InputMismatchException;

class ReadInt{
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        boolean check;
        int i = 0;
        System.out.print("Integer: ");
        do{
            check = true;
            try{
                i = in.nextInt();
            } catch (InputMismatchException e){
                System.err.println("Input error - Invalid value for an int.");
                System.out.print("Reinsert: ");
                check = false;
            }
        } while (!check);
        System.out.print(i + " + 7 = " + (i+7));
    }
}

Answer 1

Use a BufferedReader. Check NumberFormatException. Otherwise very similar to what you have. Like so …

import java.io.*;

public class ReadInt{
    public static void main(String[] args) throws Exception {
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        boolean check;
        int i = 0;
        System.out.print("Integer: ");
        do{
            check = true;
            try{
                i = Integer.parseInt(in.readLine());
            } catch (NumberFormatException e){
                System.err.println("Input error - Invalid value for an int.");
                System.out.print("Reinsert: ");
                check = false;
            }
        } while (!check);
        System.out.print(i + " + 7 = " + (i+7));
    }
}