Scanner.nextInt上的InputMismatchException

Question

I'm trying to use a Scanner to draw a rectangle in JFrame, but get these errors:

 Exception in thread "main" java.util.InputMismatchException
 at java.util.Scanner.throwFor(Unknown Source)
 at java.util.Scanner.next(Unknown Source)
 at java.util.Scanner.nextInt(Unknown Source)
 at java.util.Scanner.nextInt(Unknown Source)
 at DrawerAutoRect.main(DrawerAutoRect.java:39)

My goal of this program is to choose the type of object to draw ie: lines, rectangles,o vals, and then input the parameters, ie if it's a rectangle I'm drawing, the input would be r, 200,200,400,400 and for it to draw a rectangle with those dimensions on the JFrame. Then I'd just type "end" and it'd end waiting for objects to be input and drawn.

import java.awt.BasicStroke;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.util.Scanner;
import javax.swing.JFrame;

public class DrawerAutoRect extends JFrame {
    public DrawerAutoRect(){
    setSize(1020,1020);
}

public static void paint(Graphics g, int a, int b,int c, int d)
{
   Graphics2D g2 = (Graphics2D)g;
   g2.drawRect(a, b, c, d);
}

public static void main(String[] args) {
    int x1 = 100;
    int x2 = 100;
    int y1 = 50;
    int y2 = 50;
    Scanner s = new Scanner(System.in);
    String dim = s.next();
    while(dim!="end"){
        if(dim.equals("r")){
            x1 = s.nextInt();
            y1 = s.nextInt();
            x2 = s.nextInt();
            y2 = s.nextInt();
        }
    }
    paint(null, x1, y1, x2, y2);
    DrawerAutoRect r = new DrawerAutoRect();
    r.setDefaultCloseOperation(EXIT_ON_CLOSE);
    r.setVisible(true);
    //r.pack();
    r.setTitle("Tutorial");
}

Answer 1

The problem is that your input does not only contain the tokens you're looking for, but also commas and spaces , apparently.

Thus, you have to tell your Scanner to use a specific delimiter to understand that he has to tokenise your input stream on this String .

I'd recommend you to use the following regex as a delimiter for your Scanner :

,\s*|\s+

This would split your input on:

• any comma, followed by eventually some spaces, or
• at least one space.

Consider this sample code:

try (final Scanner s = new Scanner(System.in)) {
    s.useDelimiter(",\\s*|\\s+");

    String dim;
    do {
        dim = s.next();
        if (dim.equals("r")) {
            System.out.println(s.nextInt());
            System.out.println(s.nextInt());
            System.out.println(s.nextInt());
            System.out.println(s.nextInt());
        }
    } while (!dim.equals("end"));
}

Just by entering:

r 1, 2, 3, 4, end

... on the console, I got the following output:

1
2
3
4

... It works!

Also, as a side note, I'd like to point out that, in order to compare String s in Java , you should use the String#equals method, and not the primitive comparators.

Thus, you should use (as I did in my sample code) !dim.equals("end") instead of dim != "end" .