A conceptually terminal parser for Java using `Scanner`

TerminalInput.java

public class TerminalInput {
    private Scanner terminalScanner;

    public TerminalInput() {
        terminalScanner = new Scanner(System.in);
    }

    public String getNextLine() {
        return terminalScanner.nextLine();
    }

    protected Scanner nextLine() {
        return new Scanner(getNextLine());
    }

    public String parseNextToken(Scanner scanner) {
        return scanner.next();
    }

    public Integer parseNextInt(Scanner scanner) {
        if (scanner.hasNextInt()) {
            return scanner.nextInt();
        }
        return null;
    }

    /**
     * Get the next int value from the terminal input. This will consume the
     * next line of text and return a int value from the start of the text
     * or null if none exists
     *
     * @return Integer value or null of no int exists
     */
    public Integer getInt() {
        return parseNextInt(nextLine());
    }

    /**
     * Returns all the integers up to the first non-int value. For example
     * "1 2 3 4 a 5 6 7 8 9 0" will return `[1, 2, 3, 4]`
     *
     * @return A list of integers
     */
    public List<Integer> getInts() {
        Scanner scanner = nextLine();
        List<Integer> items = new ArrayList<>(32);
        while (scanner.hasNextInt()) {
            items.add(scanner.nextInt());
        }
        return items;
    }

    /**
     * Returns ALL the integer values input on a single line Returns all the
     * integers up to the first non-int value. For example "1 2 3 4 a 5 6 7
     * 8 9 0" will return `[1, 2, 3, 4, 5, 6, 7, 8, 9, 0]`
     *
     * @return
     */
    public List<Integer> getAllAvaliableInts() {
        Scanner scanner = nextLine();
        List<Integer> items = new ArrayList<>(32);
        while (scanner.hasNext()) {
            if (scanner.hasNextInt()) {
                items.add(scanner.nextInt());
            } else {
                // Just consume the input
                scanner.next();
            }
        }
        return items;
    }
}

For example...

TerminalInput input = new TerminalInput();

System.out.println("Enter interger");
System.out.println(input.getInt());
System.out.println("Enter some interger");
System.out.println(input.getInts());
System.out.println("Enter some more interger");
System.out.println(input.getAllAvaliableInts());

might output something like...

Enter interger
1
1
Enter some interger
1 2 3 4 5 6 7 a 8 9
[1, 2, 3, 4, 5, 6, 7]
Enter some more interger
a 1 b 2 c 3 d 4
[1, 2, 3, 4]

Requesting input and validing the result might look something like...

TerminalInput input = new TerminalInput();
Integer value = null;
do {
    System.out.print("Please enter a value between 1-4");
    value = input.getInt();
    if (value == null) {
        System.out.println("!! Invalid input");
    } else if (value < 1 || value > 4) {
        System.out.println("!! Invalid input");
        value = null;
    }
} while (value == null);
System.out.println("You have selected " + value);

What if you wanted to provide a different (non-integer) exit value?

Now you're just trying to make my life more difficult 😓

TerminalInput input = new TerminalInput();
Integer value = null;
boolean done = false;
do {
    System.out.print("Please enter a value between 1-4, [E]xit");
    Scanner scanner = input.nextLine();
    value = input.parseNextInt(scanner);
    if (value == null) {
        String text = input.parseNextToken(scanner);
        if ("e".equalsIgnoreCase(text)) {
            done = true;
        } else {
            System.out.println("!! Invalid input");
        }
    } else if (value < 1 || value > 4) {
        System.out.println("!! Invalid input");
        value = null;
    } else {
        done = true;
    }
} while (!done);
if (value != null) {
    System.out.println("You have selected " + value);
} else {
    System.out.println("You did exit");
}

Note, TerminalInput#nextLine returns a Scanner, so you don't "have" to make use of parseNextToken, you could just use the Scanner itself