Declares methods to append characters or character sequences. Any class that implements this interface can receive data formatted by a Java.Util.Formatter. The appended character or character sequence should be valid according to the rules described in Java.Lang.Character.

Appendable itself does not guarantee thread safety. This responsibility is up to the implementing class.

Implementing classes can choose different exception handling mechanism. They can choose to throw exceptions other than IOException or they do not throw any exceptions at all and use error codes instead.

[Android Documentation]