public String getExpression() {
        return this.expression;
    }
<p>
A cluster query language expression to apply to the constraint. You cannot specify an expression if the
constraint type is <code>distinctInstance</code>. To learn more, see <a
href="https://docs.aws.amazon.com/AmazonECS/latest/developerguide/cluster-query-language.html">Cluster Query
Language</a> in the Amazon Elastic Container Service Developer Guide.
</p>

@return A cluster query language expression to apply to the constraint. You cannot specify an expression if the
        constraint type is <code>distinctInstance</code>. To learn more, see <a
        href="https://docs.aws.amazon.com/AmazonECS/latest/developerguide/cluster-query-language.html">Cluster
        Query Language</a> in the Amazon Elastic Container Service Developer Guide.
aws-java-sdk-events/src/main/java/com/amazonaws/services/cloudwatchevents/model/PlacementConstraint.java