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import java.util.Comparator;
import java.util.List;

interface Validator<T> {

// Abstract method
    boolean isValid(T value);

// Default method — provides a convenience inverse
    default boolean isInvalid(T value) {
        return !isValid(value);
    }

// Default method — and-combination of validators
    default Validator<T> and(Validator<T> other) {
        return value -> this.isValid(value) && other.isValid(value);
    }

// Static factory method
    static <T> Validator<T> nonNull() {
        return value -> value != null;
    }
}

class RangeValidator implements Validator<Integer> {
    private final int min, max;
    RangeValidator(int min, int max) { this.min = min; this.max = max; }

@Override
    public boolean isValid(Integer value) {
        return value != null && value >= min && value <= max;
    }
}

interface Greetable {
    default String greet(String name) { return "Hello, " + name; }
}

interface Farewell {
    default String greet(String name) { return "Goodbye, " + name; } // same signature!
}

class ConflictResolved implements Greetable, Farewell {
    @Override
    public String greet(String name) {
        // Must override to resolve the conflict
        return Greetable.super.greet(name) + " / " + Farewell.super.greet(name);
    }
}

public class DefaultStaticMethods {
    public static void main(String[] args) {
        Validator<Integer> range   = new RangeValidator(1, 100);
        Validator<Integer> nonNull = Validator.nonNull();
        Validator<Integer> both    = nonNull.and(range);

List.of(null, -5, 0, 50, 100, 101).forEach(v ->
            System.out.printf("%-5s -> valid=%b, invalid=%b%n",
                v, both.isValid(v), both.isInvalid(v))
        );

ConflictResolved cr = new ConflictResolved();
        System.out.println(cr.greet("Alice"));
    }
}