Accepting multiple integers on a single line using Scanner

Question

The user needs to enter a certain number of integers. Rather them enter an integer at a time, I want to make it so they can enter multiple integers on a single line, then I want those integers to be converted in an array. For example, if the user enters: 56 83 12 99 then I want an array to be created that is {56, 83, 12, 99}

In other languages like Python or Ruby I would use a .split(" ") method to achieve this. No such thing exist in Java to my knowledge. Any advice on how to accept user input and create an array based on that, all on a single line?

Solution 1

Using the Scanner.nextInt() method would do the trick:

Input:

56 83 12 99

Code:

import java.util.Scanner;

class Example
{
    public static void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        int[] numbers = new int[4];
        for(int i = 0; i < 4; ++i) {
            numbers[i] = sc.nextInt();
        }
    }
}

At @user1803551's request on how Scanner.hasNext() can achieve this:

import java.util.*;

class Example2
{
    public static void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        ArrayList<Integer> numbers = new ArrayList<Integer>();
        while (sc.hasNextInt()) { // this loop breaks there is no more int input.
            numbers.add(sc.nextInt());
        }
    }
}

Solution 2

The answer by Makoto does what you want using Scanner#nextLine and String#split. The answer by mauris uses Scanner#nextInt and works if you are willing to change your input requirement such that the last entry is not an integer. I would like to show how to get Scanner#nextLine to work with the exact input condition you gave. Albeit not as practical, it does have educational value.

public static void main(String[] args) {

    // Preparation
    List<Integer> numbers = new ArrayList<>();
    Scanner scanner = new Scanner(System.in);
    System.out.println("Enter numbers:");

    // Get the input
    while (scanner.hasNextInt())
        numbers.add(scanner.nextInt());

    // Convert the list to an array and print it
    Integer[] input = numbers.toArray(new Integer[0]);
    System.out.println(Arrays.toString(input));
}

When giving the input 10 11 12 upon first prompt, the program stores them (Scanner has a private buffer), but then keeps asking for more input. This might be confusing since we give 3 integers which loop through hasNext and expect that when the 4th call is made there will be no integer and the loop will break.

To understand it we need to look at the documentation:

Both hasNext and next methods [and their primitive-type companion methods] may block waiting for further input. Whether a hasNext method blocks has no connection to whether or not its associated next method will block.

(emphasis mine) and hasNextInt

Returns: true if and only if this scanner's next token is a valid int value

What happens is that we initialized scanner with an InputStream, which is a continuous stream of data. On the 4th call to hasNextInt, the scanner "does not know" if there is a next int or not because the stream is still open and data is expected to come. To conclude from the documentation, we can say that hasNextInt

Returns true if this scanner's next token is a valid int value, returns false if it is not a valid int, and blocks if it does not know what the next token is.

So what we need to do is close the stream after we got the input:

// Get the input
numbers.add(scanner.nextInt());
System.in.close();
while (scanner.hasNextInt())
    numbers.add(scanner.nextInt());

This time we ask for the input, get all of it, close the stream to inform scanner that hasNextInt does not need to wait for more input, and store it through iteration. The only problem here is that we closed System.in, but if we don't need more input it's fine.