public String getSourceIdentifier() {
        return this.sourceIdentifier;
    }
<p>
The identifier of the event source to be added.
</p>
<p>
Constraints:
</p>
<ul>
<li>
<p>
If the source type is a DB instance, then a <code>DBInstanceIdentifier</code> must be supplied.
</p>
</li>
<li>
<p>
If the source type is a DB security group, a <code>DBSecurityGroupName</code> must be supplied.
</p>
</li>
<li>
<p>
If the source type is a DB parameter group, a <code>DBParameterGroupName</code> must be supplied.
</p>
</li>
<li>
<p>
If the source type is a DB snapshot, a <code>DBSnapshotIdentifier</code> must be supplied.
</p>
</li>
</ul>

@return The identifier of the event source to be added.</p>
        <p>
        Constraints:
        </p>
        <ul>
        <li>
        <p>
        If the source type is a DB instance, then a <code>DBInstanceIdentifier</code> must be supplied.
        </p>
        </li>
        <li>
        <p>
        If the source type is a DB security group, a <code>DBSecurityGroupName</code> must be supplied.
        </p>
        </li>
        <li>
        <p>
        If the source type is a DB parameter group, a <code>DBParameterGroupName</code> must be supplied.
        </p>
        </li>
        <li>
        <p>
        If the source type is a DB snapshot, a <code>DBSnapshotIdentifier</code> must be supplied.
        </p>
        </li>
aws-java-sdk-neptune/src/main/java/com/amazonaws/services/neptune/model/AddSourceIdentifierToSubscriptionRequest.java