public java.util.List<String> getTagKeys() {
        return tagKeys;
    }
<p>
Tag keys must be unique for a given cluster. In addition, the following restrictions apply:
</p>
<ul>
<li>
<p>
Each tag key must be unique. If you add a tag with a key that's already in use, your new tag overwrites the
existing key-value pair.
</p>
</li>
<li>
<p>
You can't start a tag key with aws: because this prefix is reserved for use by AWS. AWS creates tags that begin
with this prefix on your behalf, but you can't edit or delete them.
</p>
</li>
<li>
<p>
Tag keys must be between 1 and 128 Unicode characters in length.
</p>
</li>
<li>
<p>
Tag keys must consist of the following characters: Unicode letters, digits, white space, and the following
special characters: _ . / = + -

@.</p> </li>
       </ul>
@return <p>
        Tag keys must be unique for a given cluster. In addition, the following restrictions apply:
        </p>
        <ul>
        <li>
        <p>
        Each tag key must be unique. If you add a tag with a key that's already in use, your new tag overwrites
        the existing key-value pair.
        </p>
        </li>
        <li>
        <p>
        You can't start a tag key with aws: because this prefix is reserved for use by AWS. AWS creates tags that
        begin with this prefix on your behalf, but you can't edit or delete them.
        </p>
        </li>
        <li>
        <p>
        Tag keys must be between 1 and 128 Unicode characters in length.
        </p>
        </li>
        <li>
        <p>
        Tag keys must consist of the following characters: Unicode letters, digits, white space, and the
        following special characters: _ . / = + -
@.</p> </li>
       </ul>
aws-java-sdk-kafka/src/main/java/com/amazonaws/services/kafka/model/UntagResourceRequest.java