rspec/rules/S4973/java/rule.adoc

It's almost always a mistake to compare two instances of ``++java.lang.String++`` or boxed types like ``++java.lang.Integer++`` using reference equality ``++==++`` or ``++!=++``, because it is not comparing actual value but locations in memory.


== Noncompliant Code Example

[source,java]
----
String firstName = getFirstName(); // String overrides equals 
String lastName = getLastName();

if (firstName == lastName) { ... }; // Non-compliant; false even if the strings have the same value
----


== Compliant Solution

[source,java]
----
String firstName = getFirstName();
String lastName = getLastName();

if (firstName != null && firstName.equals(lastName)) { ... };
----


== See

* https://cwe.mitre.org/data/definitions/595.html[MITRE, CWE-595] - Comparison of Object References Instead of Object Contents
* https://cwe.mitre.org/data/definitions/597.html[MITRE, CWE-597] - Use of Wrong Operator in String Comparison
* https://wiki.sei.cmu.edu/confluence/x/UjdGBQ[CERT, EXP03-J.] - Do not use the equality operators when comparing values of boxed primitives
* https://wiki.sei.cmu.edu/confluence/x/yDdGBQ[CERT, EXP50-J.] - Do not confuse abstract object equality with reference equality


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