75 lines
2.3 KiB
Plaintext
75 lines
2.3 KiB
Plaintext
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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----
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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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----
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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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----
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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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----
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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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----
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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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----
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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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== See
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* S4973 - Strings and Boxed types should be compared using "equals()"
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* http://cwe.mitre.org/data/definitions/595.html[MITRE, CWE-595] - Comparison of Object References Instead of Object Contents
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* http://cwe.mitre.org/data/definitions/597.html[MITRE, 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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