Balking pattern

The balking pattern is a <a href="/facts/Design_pattern_(computer_science)/mV7r4egw">software design pattern</a> that only executes an action on an <a href="/facts/Object_(computer_science)/eX99dtAw">object</a> when the object is in a particular state. For example, if an object reads <a href="/facts/ZIP_file_format/qDrrYIB9">ZIP</a> files and a calling method invokes a get method on the object when the ZIP file is not open, the object would "balk" at the request. In the <a href="/facts/Java_(programming_language)/9ScgFyAL">Java</a> programming language, for example, an IllegalStateException might be thrown under these circumstances. In <a href="/facts/C_Sharp_(programming_language)/UC2gxeyb">C#</a> it would be InvalidOperationException.
There are some specialists[who?] in this field who consider balking more of an <a href="/facts/Anti-pattern/BSSJC6os">anti-pattern</a> than a design pattern. If an object cannot support its <a href="/facts/API/GMlN4vUr">API</a>, it should either limit the API so that the offending call is not available, or so that the call can be made without limitation. It should:

<ul><li>Be created in a "sane state";</li>
<li>not make itself available until it is in a sane state;</li>
<li>become a <a href="/facts/Facade_pattern/7GvBdFLH">facade</a> and answer back an object that is in a sane state.</li></ul>

Balking pattern open-in-new

Balking pattern