101 lines
2.7 KiB
Plaintext
101 lines
2.7 KiB
Plaintext
== Why is this an issue?
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It is equivalent to use the equality ``++==++`` operator and the ``++equals++`` method to compare two objects if the ``++equals++`` method inherited from ``++Object++`` has not been overridden. In this case both checks compare the object references.
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But as soon as ``++equals++`` is overridden, two objects not having the same reference but having the same value can be equal. This rule spots suspicious uses of ``++==++`` and ``++!=++`` operators on objects whose ``++equals++`` methods are overridden.
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=== Noncompliant code example
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[source,java]
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----
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String firstName = getFirstName(); // String overrides equals
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String lastName = getLastName();
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if (firstName == lastName) { ... }; // Non-compliant; false even if the strings have the same value
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----
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=== Compliant solution
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[source,java]
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----
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String firstName = getFirstName();
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String lastName = getLastName();
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if (firstName != null && firstName.equals(lastName)) { ... };
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----
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=== Exceptions
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Comparing two instances of the ``++Class++`` object will not raise an issue:
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[source,java]
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----
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Class c;
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if(c == Integer.class) { // No issue raised
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}
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----
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Comparing ``++Enum++`` will not raise an issue:
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[source,java]
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----
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public enum Fruit {
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APPLE, BANANA, GRAPE
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}
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public boolean isFruitGrape(Fruit candidateFruit) {
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return candidateFruit == Fruit.GRAPE; // it's recommended to activate S4551 to enforce comparison of Enums using ==
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}
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----
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Comparing with ``++final++`` reference will not raise an issue:
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[source,java]
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----
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private static final Type DEFAULT = new Type();
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void foo(Type other) {
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if (other == DEFAULT) { // Compliant
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//...
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}
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}
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----
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Comparing with ``++this++`` will not raise an issue:
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[source,java]
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----
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public boolean equals(Object other) {
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if (this == other) { // Compliant
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return false;
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}
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}
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----
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Comparing with ``++java.lang.String++`` and boxed types ``++java.lang.Integer++``, ... will not raise an issue.
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== Resources
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* S4973 - Strings and Boxed types should be compared using "equals()"
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* CWE - https://cwe.mitre.org/data/definitions/595[CWE-595 - Comparison of Object References Instead of Object Contents]
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* CWE - https://cwe.mitre.org/data/definitions/597[CWE-597 - Use of Wrong Operator in String Comparison]
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* https://wiki.sei.cmu.edu/confluence/x/UjdGBQ[CERT, EXP03-J.] - Do not use the equality operators when comparing values of boxed primitives
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* https://wiki.sei.cmu.edu/confluence/x/yDdGBQ[CERT, EXP50-J.] - Do not confuse abstract object equality with reference equality
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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include::../message.adoc[]
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'''
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== Comments And Links
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(visible only on this page)
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include::../comments-and-links.adoc[]
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endif::env-github,rspecator-view[]
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