CODEWITHSUNDEEP
javajava.util.scannerinputmismatchexception
psofoklis11
psofoklis11

Reputation: 37

Scanner throws InputMismatchException with null

import java.io.*;
import java.util.*;

public class Main{
    public static void main(String [] args) throws InputMismatchException{
    double width;
    int period;
    double Ppp;
    Scanner in0  = new Scanner(System.in);
    Scanner in1  = new Scanner(System.in);
    Scanner in2  = new Scanner(System.in);
    System.out.println("Give width\n");
    while(in0.hasNextDouble()){
        width = in0.nextDouble();
    }
    in0.close();
    System.out.println("\n");
    System.out.println("Give period");
    while(in1.hasNextInt()){
        period = in1.nextInt();
    }
    in1.close();
    System.out.println("\n");
    System.out.println("Insert width peak to peak");
    while(in2.hasNextDouble()){
        Ppp = in2.nextDouble();
    }
    in2.close();
}

I run this code block I insert the first input but it displays null for each input and then it crash May someone run it and tell if he has the same problem I use BlueJ compiler

Upvotes: 0

Views: 494

Answers (2)

Damian Leszczyński - Vash
Damian Leszczyński - Vash

Reputation: 30865

The cause of the problem is this 

Scanner in0  = new Scanner(System.in);
Scanner in1  = new Scanner(System.in);
Scanner in2  = new Scanner(System.in);

and this 

in0.close();
...
in1.close();
...
in2.close();

When you create the Scanner, you work on System.in, then you close it. This cause that next Scanner operate on closed stream.

The solution is to create a single Scanner for InputStream. 

Scanner scanner = new Scanner(System.in);

System.out.println("Give width\n");
double width = scanner.nextDouble();

System.out.println("Give period");
int period = scanner.nextInt();

System.out.println("\nInsert width peak to peak:");
double p2p = scanner.nextDouble();

This is only example that do not validate the user input.

Upvotes: 2

Bruno Caceiro
Bruno Caceiro

Reputation: 7189

public static void main(String [] args) throws InputMismatchException{
    double width;
    int period;
    double Ppp;
    Scanner in0  = new Scanner(System.in);

    System.out.println("Give width\n");
    // This will read the line, and parse the result as a double, this way you can insert a number and press enter
    width = Double.parseDouble(in0.nextLine());

    System.out.println("Give period");
    period = Integer.parseInt(in0.nextLine());

    System.out.println("\n");
    System.out.println("Insert width peak to peak:");
    ppp = Double.parseDouble(in0.nextLine());

    in0.close();
    }

Upvotes: 0

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