public String getExpression() {
        return this.expression;
    }
<p>
A <code>rate</code> expression or a <code>cron</code> expression that defines how often the canary is to run.
</p>
<p>
For a rate expression, The syntax is <code>rate(<i>number unit</i>)</code>. <i>unit</i> can be
<code>minute</code>, <code>minutes</code>, or <code>hour</code>.
</p>
<p>
For example, <code>rate(1 minute)</code> runs the canary once a minute, <code>rate(10 minutes)</code> runs it
once every 10 minutes, and <code>rate(1 hour)</code> runs it once every hour. You can specify a frequency between
<code>rate(1 minute)</code> and <code>rate(1 hour)</code>.
</p>
<p>
Specifying <code>rate(0 minute)</code> or <code>rate(0 hour)</code> is a special value that causes the canary to
run only once when it is started.
</p>
<p>
Use <code>cron(<i>expression</i>)</code> to specify a cron expression. For information about the syntax for cron
expressions, see <a
href="https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch_Synthetics_Canaries_cron.html">
Scheduling canary runs using cron</a>.
</p>

@return A <code>rate</code> expression or a <code>cron</code> expression that defines how often the canary is to
        run.</p>
        <p>
        For a rate expression, The syntax is <code>rate(<i>number unit</i>)</code>. <i>unit</i> can be
        <code>minute</code>, <code>minutes</code>, or <code>hour</code>.
        </p>
        <p>
        For example, <code>rate(1 minute)</code> runs the canary once a minute, <code>rate(10 minutes)</code>
        runs it once every 10 minutes, and <code>rate(1 hour)</code> runs it once every hour. You can specify a
        frequency between <code>rate(1 minute)</code> and <code>rate(1 hour)</code>.
        </p>
        <p>
        Specifying <code>rate(0 minute)</code> or <code>rate(0 hour)</code> is a special value that causes the
        canary to run only once when it is started.
        </p>
        <p>
        Use <code>cron(<i>expression</i>)</code> to specify a cron expression. For information about the syntax
        for cron expressions, see <a href=
        "https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch_Synthetics_Canaries_cron.html"
        > Scheduling canary runs using cron</a>.
aws-java-sdk-synthetics/src/main/java/com/amazonaws/services/synthetics/model/CanaryScheduleOutput.java