rspec/rules/S2159/java/rule.adoc

== Why is this an issue?

Comparisons of dissimilar types will always return false. The comparison and all its dependent code can simply be removed. This includes:

* comparing an object with null
* comparing an object with an unrelated primitive (E.G. a string with an int)
* comparing unrelated classes
* comparing an unrelated ``++class++`` and ``++interface++``
* comparing unrelated ``++interface++`` types
* comparing an array to a non-array
* comparing two arrays

Specifically in the case of arrays, since arrays don't override ``++Object.equals()++``, calling ``++equals++`` on two arrays is the same as comparing their addresses. This means that ``++array1.equals(array2)++`` is equivalent to ``++array1==array2++``.

However, some developers might expect ``++Array.equals(Object obj)++`` to do more than a simple memory address comparison, comparing for instance the size and content of the two arrays. Instead, the ``++==++`` operator or ``++Arrays.equals(array1, array2)++`` should always be used with arrays.

=== Noncompliant code example

[source,java]
----
interface KitchenTool { ... };
interface Plant {...}

public class Spatula implements KitchenTool { ... }
public class Tree implements Plant { ...}
//...

Spatula spatula = new Spatula();
KitchenTool tool = spatula;
KitchenTool [] tools = {tool};

Tree tree = new Tree();
Plant plant = tree;
Tree [] trees = {tree};


if (spatula.equals(tree)) { // Noncompliant; unrelated classes
  // ...
}
else if (spatula.equals(plant)) { // Noncompliant; unrelated class and interface
  // ...
}
else if (tool.equals(plant)) { // Noncompliant; unrelated interfaces
  // ...
}
else if (tool.equals(tools)) { // Noncompliant; array & non-array
  // ...
}
else if (trees.equals(tools)) { // Noncompliant; incompatible arrays
  // ...
}
else if (tree.equals(null)) { // Noncompliant
  // ...
}
----

== Resources

* https://wiki.sei.cmu.edu/confluence/x/5zdGBQ[CERT, EXP02-J.] - Do not use the Object.equals() method to compare two arrays

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== Implementation Specification
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include::../message.adoc[]

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== Comments And Links
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include::../comments-and-links.adoc[]
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