Double dispatch example.

Double_Dispatch_example.java

import java.util.Arrays;
import java.util.List;

public class Main {
    public static abstract class Weapon {
        protected int attackPoint;
    
        public Weapon(int attackPoint) {
            this.attackPoint = attackPoint;
        }
    
        public abstract double attackPoint(Warrior warrior);
        public abstract double attackPoint(Magician magician);
        public abstract double attackPoint(Archer archer);
    }
    
    public static abstract class Character {
        public abstract void attack(Weapon weapon);
    }
    
    public static class Sword extends Weapon {
        
        public Sword(int attackPoint) {
            super(attackPoint);
        }
        
        @Override
        public double attackPoint(Warrior warrior) {
            return this.attackPoint;
        }
    
        @Override
        public double attackPoint(Magician magician) {
            return this.attackPoint * 0.3;
        }
    
        @Override
        public double attackPoint(Archer archer) {
            return this.attackPoint * 0.5;
        }
    }
    
    public static class Arrow extends Weapon {
        
        public Arrow(int attackPoint) {
            super(attackPoint);
        }
        
        @Override
        public double attackPoint(Warrior warrior) {
            return this.attackPoint * 0.5;
        }
    
        @Override
        public double attackPoint(Magician magician) {
            return this.attackPoint * 0.3;
        }
    
        @Override
        public double attackPoint(Archer archer) {
            return this.attackPoint;
        }
    }
    
    public static class Wand extends Weapon {
        
        public Wand(int attackPoint) {
            super(attackPoint);
        }
        
        @Override
        public double attackPoint(Warrior warrior) {
            return this.attackPoint * 0.3;
        }
    
        @Override
        public double attackPoint(Magician magician) {
            return this.attackPoint;
        }
    
        @Override
        public double attackPoint(Archer archer) {
            return this.attackPoint * 0.3;
        }
    }
    
    public static class Warrior extends Character {
        @Override
        public void attack(Weapon weapon) {
            System.out.println("Warrior attack! - "+ weapon.getClass().getSimpleName() +" attack point: " + weapon.attackPoint(this));
        }
    }
    
    public static class Magician extends Character {
        @Override
        public void attack(Weapon weapon) {
            System.out.println("Magician attack! - "+ weapon.getClass().getSimpleName() +" attack point: " + weapon.attackPoint(this));
        }
    }
    
    public static class Archer extends Character {
        @Override
        public void attack(Weapon weapon) {
            System.out.println("Archer attack! - "+ weapon.getClass().getSimpleName() +" attack point: " + weapon.attackPoint(this));
        }
    }
    
    public static void main(String[] args) {
        List<Weapon> weapons = Arrays.asList(new Sword(10), new Arrow(10), new Wand(10));
        List<Character> characters = Arrays.asList(new Warrior(), new Magician(), new Archer());
        
        characters.forEach(c -> weapons.forEach(w -> c.attack(w)));
    }
}