rspec/rules/S1201/java/rule.adoc

== Why is this an issue?

"equals" as a method name should be used exclusively to override ``++Object.equals(Object)++`` to prevent any confusion.


It is tempting to overload the method to take a specific class instead of ``++Object++`` as parameter, to save the class comparison check. However, this will not work as expected when that is the only override.


=== Noncompliant code example

[source,java]
----
class MyClass {
  private int foo = 1;

  public boolean equals(MyClass o) {  // Noncompliant; does not override Object.equals(Object)
    return o != null && o.foo == this.foo;
  }

  public static void main(String[] args) {
    MyClass o1 = new MyClass();
    Object o2 = new MyClass();
    System.out.println(o1.equals(o2));  // Prints "false" because o2 an Object not a MyClass
  }
}

class MyClass2 {
  public boolean equals(MyClass2 o) {  // Ignored; `boolean equals(Object)` also present
    //..
  }

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


=== Compliant solution

[source,java]
----
class MyClass {
  private int foo = 1;

  @Override
  public boolean equals(Object o) {
    if (this == o) {
        return true;
    }
    if (o == null || getClass() != o.getClass()) {
      return false;
    }

    MyClass other = (MyClass)o;
    return this.foo == other.foo;
  }

  /* ... */
}

class MyClass2 {
  public boolean equals(MyClass2 o) {
    //..
  }

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



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

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

=== Message

Either override Object.equals(Object), or totally rename the method to prevent any confusion.


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

=== is related to: S3974

=== is related to: S1221

=== is related to: S2953

=== on 20 Aug 2013, 13:50:07 Freddy Mallet wrote:
Is implemented by \http://jira.codehaus.org/browse/SONARJAVA-300

=== on 24 Apr 2017, 10:46:16 Tibor Blenessy wrote:
I updated compliant example to not use ``++instanceof++`` operator, because that would reported as violation of RSPEC-2162

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