d3cfe19d7e
Co-authored-by: Marco Borgeaud <89914223+marco-antognini-sonarsource@users.noreply.github.com>
79 lines
2.9 KiB
Plaintext
79 lines
2.9 KiB
Plaintext
This rule raises an issue when the ``++Collections.EMPTY_*++`` fields are used instead of the ``++Collections.empty*()++`` methods.
|
|
|
|
== Why is this an issue?
|
|
|
|
Generic types (types with type parameters) have been introduced into Java with language version 1.5.
|
|
If type parameters are specified for a class or method, it is still possible to ignore them to keep backward compatibility with older code,
|
|
which is called the _raw type_ of the class or interface.
|
|
|
|
Using raw type expressions is highly discouraged because the compiler cannot perform static type checking on them.
|
|
This means that the compiler will not report typing errors about them at compile time,
|
|
but a `ClassCastException` will be thrown during runtime.
|
|
|
|
In Java 1.5, generics were also added to the Java collections API, and the data structures in `java.util`,
|
|
such as `List`, `Set`, or `Map`, now feature type parameters.
|
|
`Collections.EMPTY_LIST`, `Collections.EMPTY_SET`, and `Collections.EMPTY_MAP` are relics from before generics,
|
|
and they return raw lists, sets, or maps, with the limitations mentioned above.
|
|
|
|
== How to fix it
|
|
|
|
Use:
|
|
|
|
- `Collections.emptyList()` instead of `Collections.EMPTY_LIST`
|
|
- `Collections.emptySet()` instead of `Collections.EMPTY_SET`
|
|
- `Collections.emptyMap()` instead of `Collections.EMPTY_MAP`
|
|
|
|
In addition, there are variants of ``++Collections.empty*()++`` available also for other collection interfaces,
|
|
such as `Collections.emptyIterator()`, `Collections.emptyNavigableMap()`, `Collections.emptySortedSet()`.
|
|
|
|
=== Code examples
|
|
|
|
==== Noncompliant code example
|
|
|
|
[source,java,diff-id=1,diff-type=noncompliant]
|
|
----
|
|
List<String> collection1 = Collections.EMPTY_LIST; // Noncompliant, raw List
|
|
Set<Float> collection2 = Collections.EMPTY_SET; // Noncompliant, raw Set
|
|
Map<Int, String> collection3 = Collections.EMPTY_MAP; // Noncompliant, raw Map
|
|
----
|
|
|
|
==== Compliant solution
|
|
|
|
[source,java,diff-id=1,diff-type=compliant]
|
|
----
|
|
List<String> collection1 = Collections.emptyList(); // Compliant, List<String>
|
|
Set<Float> collection2 = Collections.emptySet(); // Compliant, Set<Float>
|
|
Map<Int, String> collection3 = Collections.emptyMap(); // Compliant, Map<Int, String>
|
|
----
|
|
|
|
== Resources
|
|
|
|
=== Documentation
|
|
|
|
* https://docs.oracle.com/javase/8/docs/api/java/util/Collections.html[Oracle - Java™ Platform, Standard Edition 8 API Specification, Class Collections]
|
|
* https://docs.oracle.com/javase/tutorial/java/generics/rawTypes.html[Oracle - The Java™ Tutorials - Raw Types]
|
|
|
|
=== Articles & blog posts
|
|
|
|
* https://www.baeldung.com/java-generics[Baeldung - The Basics of Java Generics]
|
|
|
|
ifdef::env-github,rspecator-view[]
|
|
|
|
'''
|
|
== Implementation Specification
|
|
(visible only on this page)
|
|
|
|
=== Message
|
|
|
|
Replace "Collections.EMPTY_..." by "Collections.empty...()".
|
|
|
|
|
|
'''
|
|
== Comments And Links
|
|
(visible only on this page)
|
|
|
|
=== on 4 Feb 2014, 08:48:05 Dinesh Bolkensteyn wrote:
|
|
Implemented by \http://jira.codehaus.org/browse/SONARJAVA-441
|
|
|
|
endif::env-github,rspecator-view[]
|