Raise a custom event once (game development)

Question

So, I am writing an rpg java game and decided to use custom events to simplify communication between the two classes. First I wrote "enemyDeathEvent" to let the player know if the enemy has died.

First I made my EnemyListener:

public interface EnemyListener {

    public void playerDeathEvent(EnemyEvent e);
}

After that, I created the EnemyEvent class:

public class EnemyEvent {

    private Enemy enemy;

    public EnemyEvent(Enemy enemy) {
        this.enemy = enemy;
    }

    public Enemy getSource() {
        return enemy;
    }
}

Then I create an Enemy class:

public class Enemy {

    //......
    private boolean dead;

    private Set<EnemyListener> listeners;

    public Enemy() {
        listeners = new HashSet<EnemyListener>();
    }

    //checks if the enemy is dead
    public void update() {
        if(health <= 0) dead = true;

        if(dead) fireDeathEvent();
    }

    //fires the death event
    protecd synchronized void fireDeathEvent() {
        EnemyEvent e = new EnemyEvent(this);
        for(EnemyListener listener : listeners) {
            listeners.enemyDeathEvent(e);
        }
    }

    public void addEnemyListener(EnemyListener listener) {
        listeners.add(listener);
    }  
}

Finally, when implementing an EnemyListener to a player:

public class Player implements EnemyListener {

    @Override
    public void enemyDeathEvent(EnemyEvent e) {
        System.out.println(e.getSource().getName() + " died!");
    }
}

So, when the enemy dies, the enemyDeathEvent () method from my class will be called . everything works fine , but my actual problem is that the game calls this method more than once . the reason is because my update () method is connected to a thread that updates the physics of the game, etc. 30 times per second.

@Override
public void run() {
    while(gameRunning) {
        update();
        render();
        try {
            Thread.sleep(1000/30);  //30FPS
        } catch(InterruptedException e) {
            e.printStackTrace();
        }
    }
}

, : , ?

!

Answer 1

Enemy .

- :

void update() {
    if (dead) return;
    ...
}

(, EntityBase). isEnabled :

void update() {
    if (!isEnabled) return;
    updateImpl();
}
abstract void updateImpl();

, EntityBase, updateImpl(). , , isEnabled false.

void updateImpl() {
    if(health <= 0) {
        dead = true;
        isEnabled = false;
    }
    if(dead) fireDeathEvent();
}

Answer 2

dead , :

public void update() {
    if(!dead && health <= 0) {
        dead = true;
        fireDeathEvent();
    }
}

Answer 3

You need some special condition for the enemy, which indicates the killed state and checks it in the update method