public String getExpression() {
        return this.expression;
    }
<p>
This field can contain either a Metrics Insights query, or a metric math expression to be performed on the
returned data. For more information about Metrics Insights queries, see <a
href="https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/cloudwatch-metrics-insights-querylanguage"
>Metrics Insights query components and syntax</a> in the <i>Amazon CloudWatch User Guide</i>.
</p>
<p>
A math expression can use the <code>Id</code> of the other metrics or queries to refer to those metrics, and can
also use the <code>Id</code> of other expressions to use the result of those expressions. For more information
about metric math expressions, see <a
href="https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/using-metric-math.html#metric-math-syntax"
>Metric Math Syntax and Functions</a> in the <i>Amazon CloudWatch User Guide</i>.
</p>
<p>
Within each MetricDataQuery object, you must specify either <code>Expression</code> or <code>MetricStat</code>
but not both.
</p>

@return This field can contain either a Metrics Insights query, or a metric math expression to be performed on
        the returned data. For more information about Metrics Insights queries, see <a href=
        "https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/cloudwatch-metrics-insights-querylanguage"
        >Metrics Insights query components and syntax</a> in the <i>Amazon CloudWatch User Guide</i>.</p>
        <p>
        A math expression can use the <code>Id</code> of the other metrics or queries to refer to those metrics,
        and can also use the <code>Id</code> of other expressions to use the result of those expressions. For
        more information about metric math expressions, see <a href=
        "https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/using-metric-math.html#metric-math-syntax"
        >Metric Math Syntax and Functions</a> in the <i>Amazon CloudWatch User Guide</i>.
        </p>
        <p>
        Within each MetricDataQuery object, you must specify either <code>Expression</code> or
        <code>MetricStat</code> but not both.
aws-java-sdk-cloudwatch/src/main/java/com/amazonaws/services/cloudwatch/model/MetricDataQuery.java