Validated Range (record)

/*
 * Problem : Process lines.
 * Input   : Several lines.
 * Output  : One result per line.
 * Approach: A normal class.
 * Time    : O(n)
 * Space   : O(n)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
        // Step 1: A normal class needs fields, a constructor, a check and a getter. That is a lot of code for a simple value.
        static final class Range {
            private final long low;
            private final long high;

            Range(long low, long high) {
                if (low > high) {
                    throw new IllegalArgumentException("invalid range");
                }
                this.low = low;
                this.high = high;
            }

            long length() {
                return high - low + 1;
            }
        }

    // This method solves the task. It receives the input and returns the answer.
    static String[] solve(String[] lines) {
        String[] output = new String[lines.length];
        for (int i = 0; i < lines.length; i++) {
            String[] part = lines[i].split(" ");
            // Step 2: The constructor throws for a bad range. We catch the error and print a message.
            try {
                output[i] = "length " + new Range(Long.parseLong(part[0]), Long.parseLong(part[1])).length();
            } catch (IllegalArgumentException error) {
                output[i] = error.getMessage();
            }
        }
        return output;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        java.util.List<String> all = new java.util.ArrayList<>();
        while (scanner.hasNextLine()) {
            String line = scanner.nextLine().trim();
            if (!line.isEmpty()) {
                all.add(line);
            }
        }
        String[] lines = all.toArray(new String[0]);
        System.out.println(String.join("\n", solve(lines)));
    }
}