rspec/rules/S2141/java/rule.adoc

== Why is this an issue?

Because ``++Object++`` implements ``++hashCode++``, any Java class can be put into a hash structure. However, classes that define ``++equals(Object)++`` but not ``++hashCode()++`` aren't truly hash-able because instances that are equivalent according to the ``++equals++`` method can return different hashes.


=== Noncompliant code example

[source,java]
----
public class Student {  // no hashCode() method; not hash-able
  // ...

  public boolean equals(Object o) {
    // ...
  }
}

public class School {
  private Map<Student, Integer> studentBody = // okay so far
          new HashTable<Student, Integer>(); // Noncompliant

  // ...
----


=== Compliant solution

[source,java]
----
public class Student {  // has hashCode() method; hash-able
  // ...

  public boolean equals(Object o) {
    // ...
  }
  public int hashCode() {
    // ...
  }
}

public class School {
  private Map<Student, Integer> studentBody = new HashTable<Student, Integer>();

  // ...
----



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

'''
== Implementation Specification
(visible only on this page)

=== Message

Add a "hashCode()" method to "className" or remove it from this hash.


'''
== Comments And Links
(visible only on this page)

=== on 11 Oct 2014, 11:55:56 Freddy Mallet wrote:
Perfect and relates to RSPEC-1206 without any overlap.

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