How to take input in java where array length is not defined?-CodePudding

My input is in this format:

1 2 3 4 5 6
Alice

The array length is not known. I coded it this way:

import java.util.*;
public class Main
{
    public static void main(String[] args) {
        List<Integer> arr = new ArrayList<>();
        Scanner sc = new Scanner(System.in);
        int i=0;
        while(sc.hasNext()){
            arr.add(sc.nextInt());
        }
        String player = sc.nextLine();
    }
}

But I am getting this error.

Exception in thread "main" java.util.InputMismatchException
        at java.base/java.util.Scanner.throwFor(Scanner.java:939)
        at java.base/java.util.Scanner.next(Scanner.java:1594)
        at java.base/java.util.Scanner.nextInt(Scanner.java:2258)
        at java.base/java.util.Scanner.nextInt(Scanner.java:2212)
        at Main.main(Main.java:17)

Thanks in advance.

CodePudding user response：

You should use hasNextInt to check for integer input. Once no more integers, then just use next() to read the player.

List<Integer> arr = new ArrayList<>();
Scanner sc = new Scanner(System.in);

while(sc.hasNextInt()){
    arr.add(sc.nextInt());
}
String player = sc.next();

arr.forEach(System.out::println);
System.out.println(player);

Example input's supported

10 20 30 40 50 60 70
Alice

10 20 30 40
50 60 70 Alice

10 20 30
40
50
60 70 Alice

10 20 30
40 50
60 70
Alice

output

CodePudding user response：

The reason you are seeing java.util.InputMismatchException is because you provided input "Alice" to the statement sc.nextInt(), and the scanner is telling you that it doesn't know how to convert a java.lang.String input to an int (which is the return type of nextInt()).

Here's a very simple example that reproduces the same behavior:

Scanner sc = new Scanner(System.in);
int x = sc.nextInt();

If you run those two lines and enter a non-integer, like "d", it will throw an exception:

d
Exception in thread "main" java.util.InputMismatchException
    at java.base/java.util.Scanner.throwFor(Scanner.java:939)
    at java.base/java.util.Scanner.next(Scanner.java:1594)
    at java.base/java.util.Scanner.nextInt(Scanner.java:2258)
    at java.base/java.util.Scanner.nextInt(Scanner.java:2212)
    at a91.main(a91.java:6)

To fix it, you need to replace nextInt() with something that is tolerant of non-numeric input, possibly nextLine(). Here is a (very) simple example showing how that could work. Note this is just highlighting the behavior you're asking about, namely: how to address InputMismatchException. As with your original program, there is no loop termination – it will run forever (until you quit the program).

Scanner sc = new Scanner(System.in);
int x = sc.nextInt();

while (sc.hasNext()) {
    String s = sc.nextLine();
    System.out.println("got this: "   s);
}

1 2 3 4 5 6
got this:  2 3 4 5 6
Alice
got this: Alice