public void setUsername(String username) {
        this.username = username;
    }
<p>
The value that you want to set as the username sign-in attribute. The following conditions apply to the username
parameter.
</p>
<ul>
<li>
<p>
The username can't be a duplicate of another username in the same user pool.
</p>
</li>
<li>
<p>
You can't change the value of a username after you create it.
</p>
</li>
<li>
<p>
You can only provide a value if usernames are a valid sign-in attribute for your user pool. If your user pool
only supports phone numbers or email addresses as sign-in attributes, Amazon Cognito automatically generates a
username value. For more information, see <a href=
"https://docs.aws.amazon.com/cognito/latest/developerguide/user-pool-settings-attributes.html#user-pool-settings-aliases"
>Customizing sign-in attributes</a>.
</p>
</li>
</ul>

@param username
       The value that you want to set as the username sign-in attribute. The following conditions apply to the
       username parameter.</p>
       <ul>
       <li>
       <p>
       The username can't be a duplicate of another username in the same user pool.
       </p>
       </li>
       <li>
       <p>
       You can't change the value of a username after you create it.
       </p>
       </li>
       <li>
       <p>
       You can only provide a value if usernames are a valid sign-in attribute for your user pool. If your user
       pool only supports phone numbers or email addresses as sign-in attributes, Amazon Cognito automatically
       generates a username value. For more information, see <a href=
       "https://docs.aws.amazon.com/cognito/latest/developerguide/user-pool-settings-attributes.html#user-pool-settings-aliases"
       >Customizing sign-in attributes</a>.
       </p>
       </li>
aws-java-sdk-cognitoidp/src/main/java/com/amazonaws/services/cognitoidp/model/AdminCreateUserRequest.java