Last condition not met plus strange bug

Question about the task

Under discussion

Code executes okay, just that there's this weird thing where it'll always print an extra empty string after a (Double) Entry. Help would be appreciated :)

1. Read data from the console until the word "exit" is entered.
2. For each value (except "exit"), call the print method. If the value:
2.1. contains a period ("."), then call the print method for Double;
2.2. is greater than zero, but less than 128, then call the print method for short;
2.3. less than or equal to zero or greater than or equal to 128, then call the print method for Integer;
2.4. otherwise, call the print method for String.

Requirements:

The program must read data from the keyboard.
The program should stop reading data from the keyboard after "exit" is entered.
If the entered string contains a period (".") and can be correctly converted to a Double, the print(Double value) method should be called.
If the entered string can be correctly converted to a short and the resulting number is greater than 0, but less than 128, the print(short value) method should be called.
If the entered string can be correctly converted to an Integer and the resulting number is less than or equal to 0 or greater than or equal to 128, the print(Integer value) method should be called.
In all other cases, the print(String value) method should be called.

package com.codegym.task.task15.task1519; import java.io.BufferedReader; import java.io.InputStreamReader; import java.io.IOException; import java.util.*; /* Different methods for different types */ public class Solution { public static void main(String[] args) throws IOException { //write your code here Scanner scanner = new Scanner(System.in); while (scanner.hasNext()){ if (scanner.hasNextInt()){ int n = scanner.nextInt(); if (n > 0 && n < 128){ print((short)n); } else { print((Integer)n); } } else if (scanner.hasNextDouble()){ Double x = scanner.nextDouble(); print(x); } else { String s = scanner.nextLine(); if (s.equals("exit")){ break; } print((String)s); } } scanner.close(); } public static void print(Double value) { System.out.println("This is a Double. Value: " + value); } public static void print(String value) { System.out.println("This is a String. Value: " + value); } public static void print(short value) { System.out.println("This is a short. Value: " + value); } public static void print(Integer value) { System.out.println("This is an Integer. Value: " + value); } }

Comments (7)

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Guadalupe Gagnon

Level 37 , Tampa, United States

27 May 2019, 19:44

It is because of the scanner class. When reading in strings and numbers there is a quarks where the newline character is not read in properly. You will see this occur after you enter a string that follows a number. You will need to account for this by throwing away the blank value when it occurs, or by using only scanner.nextLine() and then try parsing that input into the correct structure. You can read more here: https://stackoverflow.com/questions/13102045/scanner-is-skipping-nextline-after-using-next-or-nextfoo

Guadalupe Gagnon

Level 37 , Tampa, United States

27 May 2019, 19:49

try this:

public static void main(String[] args) throws IOException {
        //write your code here
        Scanner scanner = new Scanner(System.in);
        boolean last = false; // add here
        while (scanner.hasNext()){
            if (scanner.hasNextInt()){
                int n = scanner.nextInt();

                if (n > 0 && n < 128){
                    print((short)n);
                }

                else {
                    print(n);
                }
                last = true; //here
            }
            else if (scanner.hasNextDouble()){
                Double x = scanner.nextDouble();
                print(x);
                last = true;//here
            }
            else {
                String s =  scanner.nextLine();
                if(last) s = scanner.nextLine();
                if (s.equals("exit")){
                    break;
                }
                print(s);
                last = false; //here
            }
        }
        scanner.close();
    }

Adds 4 lines of code and should fix your issue

ThomasLC

Level 16 , Singapore, Singapore

28 May 2019, 10:15

Thanks for the link! I understand now that sc.nextInt() doesn't consume any 'end of character lines' so you need a sc.nextLine() to consume the next line and move ahead. But I don't understand your method of adding 4 boolean declarations to make it work?? Is it another alternative method to make the scanner consume leftover lines?

Guadalupe Gagnon

Level 37 , Tampa, United States

28 May 2019, 12:18

You can enter as many numbers or as many strings in a row as you want, but only need to consume the new line character when a string is entered after a number. So.... I added a boolean. It changes to true when a number is entered (line 16 and 21), then when a string is entered line 25 will only execute if the boolean is true, meaning a number was entered prior and a new line was consumed at line 24. It starts at false because the user may enter a string first. When a string is entered it also changes to false. Logically it will ONLY be true for line 25 after one to infinity numbers are entered followed by a string.

ThomasLC

Level 16 , Singapore, Singapore

29 May 2019, 02:30

Oh I didn't see line 25 has a if (last) condition. Nice workaround!

Guadalupe Gagnon

Level 37 , Tampa, United States

29 May 2019, 02:36

oops. I forgot to mark it. Ya, the rest don't make sense without that line.

Switch/Cypher

Level 25 , Bexleyheath, United Kingdom

26 September 2020, 17:12

Yes, Scanner can be weird. It drives me mad. I fixed it by only reading strings and throwing the strings over to another method to sort them out.

public class Solution {
    public static void main(String[] args) throws IOException {
        Scanner input = new Scanner(System.in);
        String x = input.nextLine();
        while (!x.equals("exit")) {
            determineInput(x);
            x = input.nextLine();
        }


    }

    public static void print(Double value) {
        System.out.println("This is a Double. Value: " + value);
    }

    public static void print(String value) {
        System.out.println("This is a String. Value: " + value);
    }

    public static void print(short value) {
        System.out.println("This is a short. Value: " + value);
    }

    public static void print(Integer value) {
        System.out.println("This is an Integer. Value: " + value);
    }


    public static void determineInput(String x) {
        try {
            if (x.contains(".")) {
                Double y = Double.parseDouble(x);
                print(y);
            } else if (Integer.parseInt(x) > 0 && Integer.parseInt(x) < 128) {
                short y = (short) Integer.parseInt(x);
                print(y);
            } else if (Integer.parseInt(x) <= 0 || Integer.parseInt(x) >= 128) {
                Integer y = Integer.parseInt(x);
                print(y);
            }
        } catch (NumberFormatException e) {
            print(x);
        }