Do not reuse the names of publicly visible identifiers, public utility classes, interfaces, or packages in the Java Standard Library.
When 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 a class name from
java.util.Vector, as specified by The Java Language Specification (JLS), §6.3.2, "Obscured Declarations" [JLS 2005], and unexpected program behavior can occur.
Well-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 §7.5.2, "Type-Import-on-Demand Declaration" [JLS 2005]) 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, which 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)
This noncompliant code example implements a class that reuses the name of the class
java.util.Vector. It attempts to introduce a different condition for the
isEmpty() method for interfacing with native legacy code by overriding the corresponding method in
java.util.Vector. Unexpected behavior can arise if a maintainer confuses the
isEmpty() method with the
Compliant Solution (Class Name)
This compliant solution uses a different name for the class, preventing any potential shadowing of the class from the Java Standard Library:
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], 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. With this technique, client code that intended to use
MyVector would remain compatible with code that uses the original implementation of
Public identifier reuse decreases the readability and maintainability of code.
An automated tool can easily detect reuse of the set of names representing public classes or interfaces from the Java Standard Library.
Puzzle 67, "All Strung Out"
Item 16, "Prefer Interfaces to Abstract Classes"
|[JLS 2005]||§6.3.2, "Obscured Declarations"|
§6.3.1, "Shadowing Declarations"
§7.5.2, "Type-Import-on-Demand Declaration"
§14.4.3, "Shadowing of Names by Local Variables"