rspec/rules/S2116/java/rule.adoc

== Why is this an issue?

The purpose of the `hashCode` method is to return a hash code based on the contents of the object.
Similarly, the purpose of the `toString`
method is to provide a textual representation of the object's contents.

Calling `hashCode()` and `toString()` directly on array instances should be avoided because the default implementations provided by the `Object` class do not provide meaningful results for arrays.
`hashCode()` returns the array's "identity hash code", and `toString()` returns nearly the same value.
Neither method's output reflects the array's contents.

== How to fix it

Use relevant static `Arrays` method.

* `Arrays.hashCode` or `Arrays.deepHashCode`
* `Arrays.toString` or `Arrays.deepToString`

=== Code examples

==== Noncompliant code example

[source,java,diff-id=1,diff-type=noncompliant]
----
public static void main(String[] args) {
    String argStr = args.toString();       // Noncompliant
    int argHash = args.hashCode();         // Noncompliant
}
----

==== Compliant solution

[source,java,diff-id=1,diff-type=compliant]
----
public static void main(String[] args) {
    String argStr = Arrays.toString(args); // Compliant
    int argHash = Arrays.hashCode(args);   // Compliant
}
----

== Resources

=== Documentation
* https://docs.oracle.com/en/java/javase/20/docs/api/java.base/java/util/Arrays.html[Oracle Java SE - Arrays API]

=== Articles & blog posts
* https://github.com/google/error-prone/blob/master/docs/bugpattern/ArrayHashCode.md[Error Prone - ArrayHashCode]


ifdef::env-github,rspecator-view[]

'''

== Implementation Specification

(visible only on this page)

=== Message

* Use "Arrays.hashCode(array)" instead.
* Use "Arrays.toString(array)" instead.


'''

== Comments And Links

(visible only on this page)

=== on 10 Oct 2014, 15:25:37 Freddy Mallet wrote:

My 2 cents @Ann:

* I would prefer a rule title like "hashCode" and "toString" methods should never be called on array instances
* I would increase the severity to "Critical"

=== on 15 Jul 2016, 14:24:30 Ann Campbell wrote:

https://github.com/google/error-prone/blob/master/docs/bugpattern/ArrayHashCode.md

endif::env-github,rspecator-view[]