Answer to Question #282570 in Java | JSP | JSF for hatipo

Question

1 Context The state pattern is a behavioral software design pattern that allows an object to alter its behavior when its internal state changes.

2 Problem description In this example, a Hero can be in one of the 3 states: ALIVE, DEAD, INVISIBLE, SILENCED defined in HeroContext. When a Hero is ALIVE with hp0, it can attack, and can be attacked, silenced and disappear. When attacked, its hp is decreased by damage. If hp=0, a Hero enters the state of DEAD with hp=0. When silenced, a Hero enters the state of SILENCED. When disappear, a Hero enters the state of INVISIBLE. When a Hero is DEAD with hp=0, it can be revived. When revived, a Hero enters the state of ALIVE with full hp. When a Hero is SILENCED, it can be attacked, recovered and disappear. When attacked, its hp is decreased by damage. If hp¡=0, a Hero enters the state of DEAD with hp=0. When recovered, a Hero enters the state of ALIVE. When disappear, a Hero enters the state of INVISIBLE. When a Hero is INVISIBLE, it can appear. 

Answer 1

public interface State {
    void dealDamage(HeroContext target, double damage);

    void takeDamage(HeroContext target, double damage);

    void disappear(HeroContext target);

    void appear(HeroContext target);

    void revive(HeroContext target);

    void silenced(HeroContext target);

    void recover(HeroContext target);
}

public class Alive implements State {
    @Override
    public void dealDamage(HeroContext target, double damage) {
        target.setHp(target.getHp() - damage);
        if (target.getHp() <= 0) {
            target.setState(new Dead());
        }
    }

    @Override
    public void takeDamage(HeroContext target, double damage) {
        target.setHp(target.getHp() - damage);
        if (target.getHp() <= 0) {
            target.setState(new Dead());
        }
    }

    @Override
    public void disappear(HeroContext target) {
        target.setState(new Invisible());
    }

    @Override
    public void appear(HeroContext target) {

    }

    @Override
    public void revive(HeroContext target) {

    }

    @Override
    public void silenced(HeroContext target) {
        target.setState(new Silenced());
    }

    @Override
    public void recover(HeroContext target) {

    }
}

public class Dead implements State {
    @Override
    public void dealDamage(HeroContext target, double damage) {

    }

    @Override
    public void takeDamage(HeroContext target, double damage) {

    }

    @Override
    public void disappear(HeroContext target) {

    }

    @Override
    public void appear(HeroContext target) {

    }

    @Override
    public void revive(HeroContext target) {
        target.setHp(HeroContext.MAX_HP);
        target.setState(new Alive());
    }

    @Override
    public void silenced(HeroContext target) {

    }

    @Override
    public void recover(HeroContext target) {

    }
}

public class Invisible implements State {
    @Override
    public void dealDamage(HeroContext target, double damage) {

    }

    @Override
    public void takeDamage(HeroContext target, double damage) {

    }

    @Override
    public void disappear(HeroContext target) {

    }

    @Override
    public void appear(HeroContext target) {
        target.setState(new Alive());
    }

    @Override
    public void revive(HeroContext target) {

    }

    @Override
    public void silenced(HeroContext target) {

    }

    @Override
    public void recover(HeroContext target) {

    }
}

public class Silenced implements State {
    @Override
    public void dealDamage(HeroContext target, double damage) {

    }

    @Override
    public void takeDamage(HeroContext target, double damage) {
        target.setHp(target.getHp() - damage);
        if (target.getHp() <= 0) {
            target.setState(new Dead());
        }
    }

    @Override
    public void disappear(HeroContext target) {
        target.setState(new Invisible());
    }

    @Override
    public void appear(HeroContext target) {

    }

    @Override
    public void revive(HeroContext target) {

    }

    @Override
    public void silenced(HeroContext target) {

    }

    @Override
    public void recover(HeroContext target) {
        target.setState(new Alive());
    }
}

public class HeroContext {
    public static final int MAX_HP = 100;
    private State state;
    private double hp;


    public HeroContext() {
        state = new Alive();
        hp = MAX_HP;
    }

    public double getHp() {
        return hp;
    }

    public void setHp(double hp) {
        this.hp = hp;
    }

    public void setState(State state) {
        this.state = state;
    }

    public void dealDamage(HeroContext target, double damage) {
        action("dealDamage", target, damage);
    }

    public void takeDamage(double damage) {
        action("takeDamage", this, damage);
    }

    public void action(String action) {
        this.action(action, this, 0);
    }

    private void action(String action, HeroContext target, double damage) {
        if (action.equalsIgnoreCase("dealDamage")) {
            state.dealDamage(target, damage);
        } else if (action.equalsIgnoreCase("takeDamage")) {
            state.takeDamage(target, damage);
        } else if (action.equalsIgnoreCase("disappear")) {
            state.disappear(target);
        } else if (action.equalsIgnoreCase("appear")) {
            state.appear(target);
        } else if (action.equalsIgnoreCase("revive")) {
            state.revive(target);
        } else if (action.equalsIgnoreCase("silenced")) {
            state.silenced(target);
        } else if (action.equalsIgnoreCase("recover")) {
            state.recover(target);
        }
    }
}