For Loop on ArrayList Exception

Question

I apologize for the limited title, but I don't know how to describe this problem exactly. I have a for loop that iterates through an arrayList containing an object. One of the objects methods is a boolean that is set at a different point in time. The point of the for loop is to go through the arrayList and remove each item that contains the boolean as false.

if(!arrayList.isEmpty()){
   int len = arrayList.size();
   for(int i=0; i<len; i++){
    if(!arrayList.get(i).isStartTimer()){
        arrayList.remove(i);
    }
  }
}

The for loop always leaves one too many objects in the array. This is because each time the for loop cycles the len drops down one because of the removed item in the array and on the last object it cancels the for loop before it can remove the object. I understand the problem, but I can't figure out how to fix it. I have tried doing something such as len+1 but it throws an indexOutOfBounds exception when I do anything to it. Any ideas? Also, is this the best way to do what I am trying to do?

Dmitry F · Accepted Answer · 2011-09-02 02:20:55Z

2

you can switch to while:

if( ! arrayList.isEmpty() ){
    int i = 0;
    while( i < arrayList.size() ) {
        if( ! arrayList.get(i).isStartTimer() ){
            arrayList.remove(i); 
            continue; // skip i++
        }
        i++;
    }
}

answered Sep 2, 2011 at 2:20

Dmitry F

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1 Comment

ryandlf Over a year ago

This would work too, thanks. I had already accepted the prior answer though, but I like this method as well.

SLaks · Accepted Answer · 2011-09-02 02:11:43Z

1

You should loop backwards so that you don't use indicies that come after the items you removed.

for (int i = arrayList.size() - 1; i >= 0; i--) {

}

Alternatively, you can just decrement i to use the next index, and get rid of the len variable so that the ending condition uses the actual length.

edited Sep 2, 2011 at 2:11

answered Sep 2, 2011 at 2:04

SLaks

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