== Why is this an issue?

In Java, the `Object.equals()` method is used for object comparison, and it is typically overridden in classes
to provide a custom equality check based on your criteria for equality.

The default implementation of `equals()` provided by the `Object` class compares the memory references of the two objects,
that means it checks if the objects are actually the same instance in memory.

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

It is important to note that when you override `equals()`, you should also override the `hashCode()`
method to maintain the contract between `equals()` and `hashCode()`.

== How to fix it

Either override `Object.equals(Object)` or rename the method.

=== Code examples

==== Noncompliant code example

[source,java,diff-id=1,diff-type=noncompliant]
----
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
  }
}
----

==== Compliant solution

[source,java,diff-id=1,diff-type=compliant]
----
class MyClass {
  private int foo = 1;

  @Override
  public boolean equals(Object o) {  // Compliant
    if (this == o) {
        return true;
    }

    if (o == null || getClass() != o.getClass()) {
      return false;
    }

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

== Resources
=== Documentation

* https://docs.oracle.com/en/java/javase/20/docs/api/java.base/java/lang/Object.html#equals(java.lang.Object)[Oracle SDK - Object.equals(Object)]

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[]