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Do not reuse the names of publicly visible identifiers, public utility classes, interfaces, or packages in the Java Standard Library.

Wiki MarkupWhen a developer uses an identifier that has the same name as a public class, such as {{Vector}}, a subsequent maintainer might be unaware that this identifier does not actually refer to {{java.util.Vector}} and might unintentionally use the custom {{Vector}} rather than the original {{java.util.Vector}} class. The custom type {{Vector}} can [shadow|BB. Glossary#shadow] a class name from {{java.util.Vector}}, as specified by the JLS, [§6§6.3.2, "Obscured Declarations"|http://java.sun.com/docs/books/jls/third_edition/html/names.html#6.3.2] \[ [JLS 2005|AA. References#JLS 05]\]. This can result in unexpected program behavior.

Wiki MarkupWell-defined import statements can resolve these issues. However, when reused name definitions are imported from other packages, use of the _type-import-on-demand declaration_ (see the JLS, [§7§7.5.2, "Type-Import-on-Demand Declaration"|http://java.sun.com/docs/books/jls/third_edition/html/packages.html#7.5.2] \[ [JLS 2005|AA. References#JLS 05]\]) can complicate a programmer's attempt to determine which specific definition was intended to be used. Additionally, a common practice that can lead to errors is to produce the import statements _after_ writing the code, often via automatic inclusion of import statements by an IDE. This creates further ambiguity with respect to the names. When a custom type is found earlier than the intended type in the Java include path, no further searches are conducted. Consequently, the wrong type is silently adopted.

Noncompliant Code Example (Class Name)

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class MyVector {
  //other code
}

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When the developer and organization control the original shadowed class, it may be preferable to change the design strategy of the original in accordance with Bloch's _Effective Java_ \[ [Bloch 2008|AA. References#Bloch 08]\], Item 16, _Prefer interfaces to abstract classes_. Changing the original class into an interface would permit class {{MyVector}} to declare that it implements the hypothetical {{Vector}} interface. This would permit client code that intended to use {{MyVector}} to remain compatible with code that uses the original implementation of {{Vector}}.

Risk Assessment

Public identifier reuse decreases the readability and maintainability of code.

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Bibliography

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[[JLS 2005AA. References#JLS 05]]	[§6.3.2, Obscured Declarationshttp://java.sun.com/docs/books/jls/third_edition/html/names.html#6.3.2]	]]></ac:plain-text-body></ac:structured-macro>
	§6.3.1, Shadowing Declarations
	§7.5.2, Type-Import-on-Demand Declaration
	§14.4.3, Shadowing of Names by Local Variables
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="8c30fcd6-f4f4-4efc-b1cb-bffaa1e404e3"><ac:plain-text-body><![CDATA[[[FindBugs 2008	AA. References#FindBugs 08]]	]]></ac:plain-text-body></ac:structured-macro>	<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="e9705f46-f876-4737-b9d9-ef3c942aab4f"><ac:plain-text-body><![CDATA[
[[Bloch 2005AA. References#Bloch 05]]	Puzzle 67. All strung out	]]></ac:plain-text-body></ac:structured-macro>	<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="49139cf8-9f9d-4b3b-8831-a8ec1e39913f"><ac:plain-text-body><![CDATA[
[[Bloch 2008AA. References#Bloch 08]]	Item 16. Prefer interfaces to abstract classes]]></ac:plain-text-body></ac:structured-macro>

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