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As a general rule, use the Object.equals() method to check whether two objects are abstractly equal to each other. Reserve use of the equality operators == and != for testing whether two references specifically refer to the same object. (This is reference equality.) Also see guideline rule "MET13-J. Classes that define an equals() method must also define a hashCode() method."
This use of the equality operators also applies to numeric boxed types (for example, Byte, Character, Short, Integer, Long, Float, and Double), although the numeric relational operators (such as <, <=, >, and >=) produce results that match those provided for arguments of the equivalent primitive numeric types. See guideline rule "EXP03-J. Do not use the equality operators when comparing values of boxed primitives" for more information.
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The Coverity Prevent Version 5.0 BAD_EQ checker can detect instances where the == operator is being used for equality of objects when, ideally, the equal method should have been used. The == operator could consider the objects to be different whereas the equals method would consider them to be the same.
Findbugs checks this guideline rule for type String.
Related Guidelines
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<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="2401ac56204c29b2-a19a85f7-45554eae-8683a1ca-8c815c0942add97a11adf02d"><ac:plain-text-body><![CDATA[ | [[JLS 2005 | AA. Bibliography#JLS 05]] | [§3.10.5, "String Literals" | http://java.sun.com/docs/books/jls/third_edition/html/lexical.html#3.10.5] | ]]></ac:plain-text-body></ac:structured-macro> |
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<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="4711b4261b1187ef-adfc0bb8-440e4f87-b48eb625-fd33e8a536ff8a48d8b93e74"><ac:plain-text-body><![CDATA[ | [[Rogue 2000 | AA. Bibliography#Rogue 2000]] | Rule 79: Use | ]]></ac:plain-text-body></ac:structured-macro> |
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