JAVA：扫描器无法读取下一行// //返回空字符串

Question

So I am programming Snake at the moment and i have a Method to read an an integer value from the console.
When my Method throws a mistake - or atleast when i return to that method - it doesn't read in a new line from input but just passes aa empty string.
Here is my code:

static int readInInt()
{
    //We Read in the next line the user enters
    String s = sc.nextLine();
    //x returns -1 if mistake happens
    int x = -1;

    try
    {
        //Now we try to parse that int
        x = Integer.parseInt(s);
        x = Math.abs(x);
        System.out.println("Setting the speed to " + (x*100) + "ms.");
    }
    catch(NumberFormatException ex)
    {
        //If we can't parse it we try to get the ints with a regex and then parse it
        System.out.println("Du hast eine nummer eingetippt die das System nicht analysieren kann.");
        System.out.println("Das System probiert jetzt die Nummer die du eingetippt hast über umwege zu Analysieren.");
        s = s.replaceAll("[^-?0-9]+", "");   
        try
        {
            x = Integer.parseInt(s);
        }
        catch(Exception e)
        {
            //and if that doesnt work we just say Error!
            System.out.println("Error Handling didn't work.\n"
                    + "Please try again with just a simple number (e.g. 7)");            
            //Return an Error in form of -1
            return -1;
        }
        x = Math.abs(x);
        System.out.println("Setting the speed to " + (x*100) + "ms.");
    }

    return x;
}

I've declared "sc" as a static class variable static Scanner sc = new Scanner(System.in); at the beginnning of my programm.

Why does the scanner return an empty String? - without asking for user input -
And yes i am aware of the Method .readNextInt, but i find it easyer to handle exceptions like this.

Answer 1

Thanks @Seelenvirtuose who brought me to the right track of the solution!

I said, if in another place sc.nextInt() was used, you have a pending newline that was not consumed. The next sc.nextLine() only consumes this newline and does not give the priority to enter anything. The problem, therefore, is in another portion of your code! –

The solution was that in some parts of my code i was using sc.next() which only reads in the next string untill the whitespace (if i am not mistaken) and not sc.nextLine() .
So I've changed all sc.next() to sc.nextLine() not it works just fine.

There are 2 other solutions that I've found while doing trail and error:
a) Write sc.reset() which does " Resetting a scanner discards all of its explicit state information[...] " bevor accesing the sc.nextLine() command or
b) Just create a new instance of the Scanner class.

Thanks again to Seelenvirtuose .

Answer 2

I solved using two different scanner: one for reading of int and float values and another for reading String.

Scanner scanString = new Scanner(System.in);
Scanner scanIntFloat = new Scanner(System.in);

int cod = scanIntFloat.nextInt();
String name = scanString.nextLine();

Elias.

Answer 3

You can use two different Scanners .......

First Scanner for reading int , float and double .

Second Scanner for reading String values.

Like Below......

Scanner scanIntFloat = new Scanner(System.in);
Scanner scanString = new Scanner(System.in);

int cod = scanIntFloat.nextInt();
String name = scanString.nextLine();

Answer 4

Had a similar issue. What i did was add a nextLine(); command after the next(); command to catch the character filling up the buffer that is inserted where you put your input request.

Basically:

• word = scan.next(); --Input whatever word you need
• catcher = scan.nextLine(); --Catches the character that fills up the buffer
• input2 = scan.nextLine(); --Input your following line

Hope this helps :)