public void setKey(String key) {
        this.key = key;
    }
<p>
<i>Required</i>. A string used to identify this tag. You can specify a maximum of 128 characters for a tag key.
Tags owned by Amazon Web Services (Amazon Web Services) have the reserved prefix: <code>aws:</code>.
</p>

@param key
       <i>Required</i>. A string used to identify this tag. You can specify a maximum of 128 characters for a tag
       key. Tags owned by Amazon Web Services (Amazon Web Services) have the reserved prefix: <code>aws:</code>.
aws-java-sdk-cloudformation/src/main/java/com/amazonaws/services/cloudformation/model/Tag.java