Java – hashcode and equals are collections unmodifiableCollection()

Collections class has some static help methods to provide read-only views of various collection types, such as unmodifiableset(), unmodifiablelist(), etc For these view objects, the hashcode () and equals () methods forward calls to the underlying collection... With a strange exception: unmodifiablecollection()

JavaDoc explicitly states：

My question: if the background collection is a collection or list, I want the behavior to be consistent with unmodifiableset() and unmodifiablelist() How to breach a hashcode / equal contract?

Solution

From Javadoc for collection:

An unmodifiablelist is an unmodifiablecollection, but the opposite is not the opposite - an unmodifiablecollection wraps a list, not an unmodifiablelist Therefore, if an unmodifiablecollection containing list a is compared with an unmodifiablelist containing the same list a, the two wrappers should not be equal If you just pass the packing list, they will be equal