wro4j-core/src/main/java/ro/isdc/wro/model/group/Group.java
public Group addResource(final Resource resource) {
    notNull(resource);
    synchronized (this) {
      if (!hasResource(resource)) {
        resources.add(resource);
      } else {
        LOG.debug("Resource {} is already contained in this group, skipping it.", resource);
      }
    }
    return this;
  }
public Group addResource(final Resource resource) {
    notNull(resource);
    synchronized (this) {
      if (!hasResource(resource)) {
        resources.add(resource);
      } else {
        LOG.debug("Resource {} is already contained in this group, skipping it.", resource);
      }
    }
    return this;
  }
Add a {@link Resource} to the collection of resources associated with this group.
<p/>
The implementation is synchronized, because it mutates the collection.

@param resource
{@link Resource} to add to this group (at the end).
@return the reference to Group (fluent interface).