rspec/rules/S4551/java/rule.adoc

== Why is this an issue?

Testing equality of an enum value with ``++equals++`` is perfectly valid because an enum is an Object and every Java developer knows "==" should not be used to compare the content of an Object. At the same time, using "==" on enums:

* provides the same expected comparison (content) as ``++equals++``
* is more null-safe than equals()
* provides compile-time (static) checking rather than runtime checking

For these reasons, use of "==" should be preferred to ``++equals++``.


=== Noncompliant code example

[source,java]
----
public enum Fruit {
   APPLE, BANANA, GRAPE
}

public enum Cake {
  LEMON_TART, CHEESE_CAKE
}

public boolean isFruitGrape(Fruit candidateFruit) {
  return candidateFruit.equals(Fruit.GRAPE); // Noncompliant; this will raise an NPE if candidateFruit is NULL
}

public boolean isFruitGrape(Cake candidateFruit) {
  return candidateFruit.equals(Fruit.GRAPE); // Noncompliant; always returns false
}
----


=== Compliant solution

[source,java]
----
public boolean isFruitGrape(Fruit candidateFruit) {
  return candidateFruit == Fruit.GRAPE; // Compliant; there is only one instance of Fruit.GRAPE - if candidateFruit is a GRAPE it will have the same reference as Fruit.GRAPE
}

public boolean isFruitGrape(Cake candidateFruit) {
  return candidateFruit == Fruit.GRAPE; // Compliant; compilation time failure
}
----


== Resources

* https://www.javaworld.com/article/2074292/core-java/use-----or-----to-compare-java-enums.html[Use ++==++ (or !=) to Compare Java Enums]


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