current modification exception in java while removing from array list

Question

  public void removeVehicle(String licenseNum){      

      for (Vehicle vehicle : vehicleLot){

    String flag = vehicle.getLicenseNumber().toString();
        if(flag.compareTo(licenseNum) == 0){
            int num = vehicleLot.indexOf(vehicle);

        vehicleLot.remove(num);
    }

I am getting this exception, I am trying to remove a vehicle from a array list where it matched the license number like above.

my array list is like this private

 List<Vehicle> vehicleLot = new ArrayList<Vehicle>();

It's "CONcurrent modification exception" -- you're modifying something concurrent with it being iterated. Don't do that. (At least not that way.) — Hot Licks
– Hot Licks, Commented Aug 15, 2014 at 1:11

Trevor Freeman · Accepted Answer · 2014-08-15 00:30:05Z

2

You cannot remove an element from an ArrayList that you are iterating through using an Iterator (which is what for(element : list) uses under the covers) unless you use the iterator itself to remove the item.

What you can do is to iterate through the list using a declared iterator, or via numeric index to avoid the issue.

E.g.

Iterator<Vehicle> iterator = vehicleLot.iterator();
while(iterator.hasNext())
{
  Vehicle vehicle = iterator.next();
  String flag = vehicle.getLicenseNumber().toString();
  if(flag.compareTo(licenseNum) == 0)
  {
    iterator.remove();
  }

}

answered Aug 15, 2014 at 0:30

Trevor Freeman

7,2722 gold badges23 silver badges41 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

purplehaze Over a year ago

could you please exapand on this? I am not sure what you mean how would i combine delcared iterator and the above for each

Trevor Freeman Over a year ago

@purplehaze Replace your foreach with the while loop I have provided.

Smith_61 · Accepted Answer · 2014-08-15 00:29:35Z

1

The foreach loop in java is not a true runtime feature. It's just syntax to replace one of two loops.

On those that implement Iterable< T > the loop is effectively

Iterator< T > itr = list.iterator();
while( itr.hasNext() ) {
    T t = itr.next();
    // Loop stuff
}

This means you can not edit the List in a foreach loop without causing an exception and you must abide by all the restrictions set in place when using Iterators without the benefit of having access to the iterator.

On array's it is effectively

T[] arr = ...;
for( int i = 0; i < arr.length; i++ ) {
    T elm = arr[ i ];
    // Loop stuff
}

answered Aug 15, 2014 at 0:29

Smith_61

2,08813 silver badges12 bronze badges

1 Comment

purplehaze Over a year ago

could you possible expand on the solution? how would i use this Itertor on my above loop?

Hot Licks · Accepted Answer · 2014-08-15 01:18:17Z

0

The old way to handle this (before fancy iterators) was:

public void removeVehicle(String licenseNum){      
    for (int i = vehicleLot.size() - 1; i >= 0; i--) {
        Vehicle vehicle = vehicleLot.get(i);
        String flag = vehicle.getLicenseNumber().toString();
        if (flag.equals(licenseNum)) {
           vehicleLot.remove(i);
        }
    }
}

answered Aug 15, 2014 at 1:18

Hot Licks

47.8k19 gold badges96 silver badges156 bronze badges

Collectives™ on Stack Overflow

current modification exception in java while removing from array list

3 Answers 3

2 Comments

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related