Adapter: Temperature Sensors

/*
 * Problem : Process lines.
 * Input   : Several command lines.
 * Output  : One Celsius value per line.
 * Approach: Adapter classes.
 * Time    : O(n)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
        // Step 1: The interface that the main loop wants to use.
        interface CelsiusSensor {
            long celsius();
        }

        // Step 2: Old classes that we cannot change. Each has its own method name and unit.
        static class FahrenheitDevice {
            final long degrees;

            FahrenheitDevice(long degrees) {
                this.degrees = degrees;
            }

            long readFahrenheit() {
                return degrees;
            }
        }

        static class KelvinDevice {
            final long degrees;

            KelvinDevice(long degrees) {
                this.degrees = degrees;
            }

            long readKelvin() {
                return degrees;
            }
        }

        // Step 3: Adapters wrap an old object and make it look like a CelsiusSensor.
        static class FahrenheitAdapter implements CelsiusSensor {
            private final FahrenheitDevice device;

            FahrenheitAdapter(FahrenheitDevice device) {
                this.device = device;
            }

            public long celsius() {
                return Math.floorDiv((device.readFahrenheit() - 32) * 5, 9);
            }
        }

        static class KelvinAdapter implements CelsiusSensor {
            private final KelvinDevice device;

            KelvinAdapter(KelvinDevice device) {
                this.device = device;
            }

            public long celsius() {
                return device.readKelvin() - 273;
            }
        }

    // 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(" ");
            long value = Long.parseLong(part[1]);
            CelsiusSensor sensor;
            if (part[0].equals("fahrenheit")) {
                sensor = new FahrenheitAdapter(new FahrenheitDevice(value));
            } else if (part[0].equals("kelvin")) {
                sensor = new KelvinAdapter(new KelvinDevice(value));
            } else {
                sensor = () -> value;
            }
            output[i] = String.valueOf(sensor.celsius());
        }
        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)));
    }
}