27 lines
799 B
Markdown
27 lines
799 B
Markdown
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---
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layout: pattern
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title: Singleton
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folder: singleton
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categories: pattern_cat
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tags: pattern_tag
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---
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**Intent:** Ensure a class only has one instance, and provide a global point of
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access to it.
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**Applicability:** Use the Singleton pattern when
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* there must be exactly one instance of a class, and it must be accessible to clients from a well-known access point
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* when the sole instance should be extensible by subclassing, and clients should be able to use an extended instance without modifying their code
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**Typical Use Case:**
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* the logging class
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* managing a connection to a database
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* file manager
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**Real world examples:**
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* [java.lang.Runtime#getRuntime()](http://docs.oracle.com/javase/8/docs/api/java/lang/Runtime.html#getRuntime%28%29)
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