Removing from an arraylist android

Question

I have an android game which involves a ship shooting enemies. I am trying to make it so that if the enemies are within a certain distance of the ammos, then the enemys remove themselves from the screen. I have attempted to do it and the code compiles, but i am unsure why the enemys arent being removed from the screen once been hit. Can anyone see anything wrong with the code below? Thankyou

for (TopEnemy i : newTopEnemy)
{
    for (int q = 0; q < ammo.length; q++)
    {
       float xsubs = i.enemyX - ammo[q].positionX;
       float ysubs = i.enemyY - ammo[q].positionY;
       float squared = (xsubs * xsubs) + (ysubs * ysubs);
       float distance = (float)Math.sqrt(squared);
       if (distance < 10.0)
       {
          newTopEnemy.remove(q);
       }
    }
 }

Vlad · Accepted Answer · 2014-03-17 11:47:32Z

5

Shouldn't it be newTopEnemy.remove(i); ? q looks like an index on ammo.

answered Mar 17, 2014 at 11:47

Vlad

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Comments

Salah · Accepted Answer · 2014-03-17 11:50:44Z

3

You need to use Iteratore.remove.

for (Iterator<TopEnemy> itr = intList2.iterator(); iterator.hasNext();) {
    TopEnemy enemy = itr.next();
    //code here 
    if (distance < 10.0) {
            itr.remove();
    }
}

answered Mar 17, 2014 at 11:50

Salah

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2 Comments

user3426043 Over a year ago

So it should look something like this? 'for (Iterator<TopEnemy> itr = intList2.iterator(); iterator.hasNext();) { TopEnemy enemy = itr.next(); for (TopEnemy i : newTopEnemy) { for (int q = 0; q < ammo.length; q++) { float xsubs = i.enemyX - ammo[q].positionX; float ysubs = i.enemyY - ammo[q].positionY; float squared = (xsubs * xsubs) + (ysubs * ysubs); float distance = (float) Math.sqrt(squared); if (distance < 10.0) { itr.remove(); } } } }'

Salah Over a year ago

@user3426043 the iterator should be replaced by your for-each loop.

anirudh · Accepted Answer · 2014-03-17 11:50:41Z

1

You cannot remove from a list while using the foreach loop. You have to use an iterator to loop through the list and then remove using the remove method.

answered Mar 17, 2014 at 11:50

anirudh

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Comments

cosmincalistru · Accepted Answer · 2014-03-17 11:51:53Z

0

I would add to Vlad answer that is not always a good ideea to remove an item while looping over a list like that. I would do it like this :

for (int i = newTopEnemy.size()-1;i>=0;i--) {
    TopEnemy enemy = newTopEnemy.get(i);
    for (int q = 0; q < ammo.length; q++) {
        float xsubs = enemy.enemyX - ammo[q].positionX;
        float ysubs = enemy.enemyY - ammo[q].positionY;
        float squared = (xsubs * xsubs) + (ysubs * ysubs);
        float distance = (float)Math.sqrt(squared);
        if (distance < 10.0) {
            newTopEnemy.remove(i);
            break;
        }
    }
}

answered Mar 17, 2014 at 11:51

cosmincalistru

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1 Comment

Blackbelt Over a year ago

this way, if you are lucky you'll get an ArrayIndexOutBoundException

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