rspec/rules/S4454/java/rule.adoc

By contract, the ``++equals(Object)++`` method, from ``++java.lang.Object++``, should accept a ``++null++`` argument. Among all the other cases, the ``++null++`` case is even explicitly detailed in the ``++Object.equals(...)++`` Javadoc, stating _"For any non-null reference value x, x.equals(null) should return false."_


Assuming that the argument to ``++equals++`` is always non-null, and enforcing that assumption with an annotation is not only a fundamental violation of the contract of ``++equals++``, but it is also likely to cause problems in the future as the use of the class evolves over time.


The rule raises an issue when the ``++equals++`` method is overridden and its parameter annotated with any kind of ``++@Nonnull++`` annotation.


== Noncompliant Code Example

----
public boolean equals(@javax.annotation.Nonnull Object obj) { // Noncompliant
  // ...
}
----


== Compliant Solution

----
public boolean equals(Object obj) {
  if (obj == null) {
    return false;
  }
  // ... 
}
----



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