public java.util.List<CostCategoryRule> getRules() {
        return rules;
    }
<p>
The <code>Expression</code> object used to categorize costs. For more information, see <a
href="https://docs.aws.amazon.com/aws-cost-management/latest/APIReference/API_CostCategoryRule.html"
>CostCategoryRule </a>.
</p>

@return The <code>Expression</code> object used to categorize costs. For more information, see <a
        href="https://docs.aws.amazon.com/aws-cost-management/latest/APIReference/API_CostCategoryRule.html"
        >CostCategoryRule </a>.
aws-java-sdk-costexplorer/src/main/java/com/amazonaws/services/costexplorer/model/UpdateCostCategoryDefinitionRequest.java