How to use the aws-cdk.PolicyStatement function in aws-cdk

const subscriptionName = queue.name + 'Subscription';
        if (this.tryFindChild(subscriptionName)) {
            throw new Error(`A subscription between the topic ${this.name} and the queue ${queue.name} already exists`);
        }

        // we use the queue name as the subscription's. there's no meaning to subscribing
        // the same queue twice on the same topic.
        const sub = new Subscription(this, subscriptionName, {
            topic: this,
            endpoint: queue.queueArn,
            protocol: SubscriptionProtocol.Sqs
        });

        // add a statement to the queue resource policy which allows this topic
        // to send messages to the queue.
        queue.addToResourcePolicy(new PolicyStatement()
            .addResource(queue.queueArn)
            .addAction('sqs:SendMessage')
            .addServicePrincipal('sns.amazonaws.com')
            .setCondition('ArnEquals', { 'aws:SourceArn': this.topicArn }));

        return sub;
    }

public get eventRuleTarget(): EventRuleTarget {
        if (!this.eventRuleTargetPolicyAdded) {
            this.addToResourcePolicy(new PolicyStatement()
                .addAction('sns:Publish')
                .addPrincipal(new ServicePrincipal('events.amazonaws.com'))
                .addResource(this.topicArn));

            this.eventRuleTargetPolicyAdded = true;
        }

        return {
            id: this.name,
            arn: this.topicArn,
        };
    }
}

public grantPublish(identity?: IIdentityResource) {
        if (!identity) {
            return;
        }

        identity.addToPolicy(new PolicyStatement()
            .addResource(this.topicArn)
            .addActions('sns:Publish'));

        this.addToResourcePolicy(new PolicyStatement()
            .addResource('*')
            .addPrincipal(identity.principal)
            .addActions('sns:Publish'));
    }