Page History

...

EXP04-EX1: The collections framework equals() method also takes an argument of type Object, but it is acceptable to pass an object of a different type from that of the underlying collection/map to the equals() method. Doing so cannot cause any confusion because the contract of the equals() method stipulates that objects of different classes will never be equivalent . See (see MET08-J. Preserve the equality contract when overriding the equals() method for more information).

EXP04-EX2: Some Java programs, particularly legacy programs, may iterate through a collection of variously typed objects with the expectation that only those objects with the same type as the collection parameter will be operated on. An exception is allowed in cases where when there is no expectation that the operation is not a no-op.

...

[Core Java 2004]	Chapter 5, "Inheritance"
[JCF 2014]	The Java Collections Framework
[JLS 2005]	§5.1.7, Boxing Conversions
[Seacord 2015]	IDS17-J. Prevent XML External Entity Attacks LiveLesson
[Techtalk 2007]	"The Joy of Sets"

...