Balking pattern

This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these messages) This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Balking pattern" – news · newspapers · books · scholar · JSTOR (December 2010) (Learn how and when to remove this message) This article includes a list of general references, but it lacks sufficient corresponding inline citations. Please help to improve this article by introducing more precise citations. (December 2010) (Learn how and when to remove this message) This article's lead section contains information that is not included elsewhere in the article. If this information is appropriate for the lead of the article, it should also be included in the article's body. Relevant discussion may be found on the talk page. (July 2023) (Learn how and when to remove this message) (Learn how and when to remove this message)

The balking pattern is a software design pattern that only executes an action on an object when the object is in a particular state. For example, if an object reads ZIP 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 Java programming language, for example, an IllegalStateException might be thrown under these circumstances. In C# it would be InvalidOperationException.

There are some specialists^[who?] in this field who consider balking more of an anti-pattern than a design pattern. If an object cannot support its API, 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:

• Be created in a "sane state";^{[further explanation needed]}
• not make itself available until it is in a sane state;
• become a facade and answer back an object that is in a sane state.