Why Aren't Java Collections' `remove()` Methods Generic?

Why Are Java Collections' Remove Methods Not Generic?

The Java Collections framework provides a remove() method for both collections and maps. However, this method is not generic, meaning it accepts an Object as an argument rather than an E type parameter. This decision has raised questions about the potential benefits of making remove() generic.

One argument for making remove() generic is that it could prevent compile-time errors when accidentally attempting to remove an incompatible type from a collection. For instance, if a Collection is accidentally passed a Set, it would result in a compile-time error rather than a debugging issue later on.

However, the reason why remove() is not generic is primarily because it allows for the removal of objects based on equality rather than strict type checking. According to the remove() method specification, the element to be removed is identified as an object e such that (o==null ? e==null : o.equals(e)) is true. This allows for flexibility in element removal, as the removed object does not need to be the same type as the object passed to the remove() method.

As an example, it is possible to have a Map. When calling remove() with a LinkedList as an argument, it should remove the key that is a list with the same contents, even if it is a different implementation of List. This would not be possible if remove() were generic and restricted to a single type parameter.

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