The Strategy Pattern : It defines a family of algorithms, encapsulates each one, and makes them interchangeable. Strategy lets the algorithm vary independently from clients that use it.

1.WeaponBehaviour.java

package com.chp1.designpuzzle;

public interface WeaponBehaviour {
    String useWeapon();
}

2.SwordBehaviour.java

package com.chp1.designpuzzle;

public class SwordBehaviour implements WeaponBehaviour{

    @Override
    public String useWeapon() {
        return ("I use sword when fighting.");
    }
    
}

3.KnifeBehaviour.java

package com.chp1.designpuzzle;

public class KnifeBehaviour implements WeaponBehaviour{

    @Override
    public String useWeapon() {
        return("I use knife when fighting.");
    }
    
}

4.BowAndArrowBehaviour.java

package com.chp1.designpuzzle;

public class BowAndArrowBehaviour implements WeaponBehaviour{

    @Override
    public String useWeapon() {
        return("I use bow and arrow when fighting.");
    }
    
}

5. AxeBehaviour.java

package com.chp1.designpuzzle;

public class AxeBehaviour implements WeaponBehaviour{

    @Override
    public String useWeapon() {
        return("I use my axe!!!");
    }
    
}

6. Character.java

package com.chp1.designpuzzle;

public abstract class Character {
    WeaponBehaviour weapon;
    
    public abstract void fight();
    
    public void setWeapon(WeaponBehaviour wp){
        this.weapon = wp;
    }
}

7.King.java

package com.chp1.designpuzzle;

public class King extends Character{

    @Override
    public void fight() {
        System.out.println("I fight like a king. " + weapon.useWeapon());
    }
    
}

8.Queen.java

package com.chp1.designpuzzle;

public class Queen extends Character{

    @Override
    public void fight() {
        System.out.println("I fight like a queen ." + weapon.useWeapon());
    } 
    
}

9. Tester.java

    @Test
    public void test_fighting_game(){
        
        King k = new King();
        //Lets change the weapon at run time
        k.setWeapon(new AxeBehaviour());
        k.fight();
        
        //Change again
        k.setWeapon(new BowAndArrowBehaviour());
        k.fight();
    }

z.out.txt

I fight like a king. I use my axe!!!
I fight like a king. I use bow and arrow when fighting.