Generics: RedRover 2024 Spring Lecture 16

animals.Animal.java

package animals;

public class Animal {
    private final String name;
    private final double weight;
    private final double canLiftWeight;

    public Animal(String name, double weight, double canLiftWeight) {
        this.name = name;
        this.weight = weight;
        this.canLiftWeight = canLiftWeight;
    }

    public String getName() {
        return name;
    }

    public double getWeight() {
        return weight;
    }

    public double getCanLiftWeight() {
        return canLiftWeight;
    }
}

animals.Animals.java

package animals;

import comparators.GenericComparator;

public class Animals {
    private Animals() {}

    public static final Animal TIGER = new Animal("Тигр", 550, 1100);
    public static final Animal ELEPHANT = new Animal("Слон", 4000, 6800);
    public static final Animal BEAR = new Animal("Медведь", 500, 500);
    public static final Animal ANT = new Animal("Муравей", 0.000003, 0.000060);
    public static final Animal DUNG_BEETLE = new Animal("Навозный Жук", 0.002, 2.282);

    public static final GenericComparator<Animal> HEAVIEST = new GenericComparator<Animal>() {
        @Override
        public int compare(Animal a, Animal b) {
            if (a.getWeight() > b.getWeight()) return 1;
            if (a.getWeight() < b.getWeight()) return -1;
            return 0;
        }
    };

    public static final GenericComparator<Animal> STRONGEST = new GenericComparator<Animal>() {
        @Override
        public int compare(Animal a, Animal b) {
            double relativeWeightA = a.getCanLiftWeight() / a.getWeight();
            double relativeWeightB = b.getCanLiftWeight() / b.getWeight();
            if (relativeWeightA > relativeWeightB) return 1;
            if (relativeWeightA < relativeWeightB) return -1;
            return 0;
        }
    };
}

animals.Main.java

package animals;

import comparators.Comparators;
import static animals.Animals.*;

import java.util.List;

public class Main {
    public static void main(String[] args) {
        System.out.println(Comparators.findBest(
                List.of(TIGER, ELEPHANT, BEAR, ANT, DUNG_BEETLE),
                STRONGEST
        ).getName());
    }
}

comparators.Comparators.java

package comparators;

import java.util.List;

public class Comparators {

    public static final GenericComparator<Integer> MORE = new GenericComparator<Integer>() {
        @Override
        public int compare(Integer a, Integer b) {
            if (a > b) return 1;
            if (a < b) return -1;
            return 0;
        }
    };

    public static final GenericComparator<Integer> ABS_MORE = new GenericComparator<Integer>() {
        @Override
        public int compare(Integer a, Integer b) {
            return MORE.compare(Math.abs(a), Math.abs(b));
        }
    };

    public static final GenericComparator<String> LONGEST_STRING = new GenericComparator<String>() {
        @Override
        public int compare(String a, String b) {
            if (a.length() > b.length()) return 1;
            if (a.length() < b.length()) return -1;
            return 0;
        }
    };

    public static <T> T findBest(List<T> elements, GenericComparator<T> comparator) {
        if (elements.size() == 0) return null;
        T champion = elements.get(0);
        for (int i = 1; i < elements.size(); i++) {
            if (comparator.compare(elements.get(i), champion) > 0) {
                champion = elements.get(i);
            }
        }
        return champion;
    }

}

comparators.GenericComparator.java

package comparators;

public interface GenericComparator<T>  {
    int compare(T a, T b);
}

comparators.IntegerLess.java

package comparators;

public class IntegerLess implements GenericComparator<Integer> {
    @Override
    public int compare(Integer a, Integer b) {
        if (a < b) return 1;
        if (a > b) return -1;
        return 0;
    }
}