public void update(long currentTime){
        if(currentTime - lastUpdate > duration){        
            lastUpdate = currentTime;
            if (this.indexEnemyArray < this.enemyArrayLv1.length){
                for (int i=0;i<enemyArrayLv1[indexEnemyArray].length();i++){
                    world.addEnemy(getSpecEnemy(enemyArrayLv1[indexEnemyArray].charAt(i)));  
                }
            } else {
                world.notifyWaveEnd();
            }
            indexEnemyArray+=1;
        }
    }