public void setGroups(java.util.Collection<java.util.List<String>> groups) {
        if (groups == null) {
            this.groups = null;
            return;
        }

        this.groups = new java.util.ArrayList<java.util.List<String>>(groups);
    }
<p>
Specifies the fields to group by.
</p>

@param groups
       Specifies the fields to group by.
aws-java-sdk-glue/src/main/java/com/amazonaws/services/glue/model/Aggregate.java