public void setActiveInstances(java.util.Collection<ActiveInstance> activeInstances) {
        if (activeInstances == null) {
            this.activeInstances = null;
            return;
        }

        this.activeInstances = new com.amazonaws.internal.SdkInternalList<ActiveInstance>(activeInstances);
    }
<p>
The running instances. This list is refreshed periodically and might be out of date.
</p>

@param activeInstances
       The running instances. This list is refreshed periodically and might be out of date.
aws-java-sdk-ec2/src/main/java/com/amazonaws/services/ec2/model/DescribeFleetInstancesResult.java