The statement

File f = null;

is valid and useful (I don't think I need to explain why). It is likewise useful to have a collection of files, some of which may be null.

List<File> files = new ArrayList<File>();
files.add(null);

The usefulness of collections that may contain null objects proceeds directly from the usefulness of objects that may be null. It is really as simple as that.

The statement

File f = null;

is valid and useful (I don't think I need to explain why). It is likewise useful to have a collection of files, some of which may be null.

List<File> files = new ArrayList<File>();
// use my collection of files
// ....
// not using this one anymore:
files.set(3, null);

The usefulness of collections that may contain null objects proceeds directly from the usefulness of objects that may be null. It is really as simple as that.

If

File f = null;

is valid and useful (it is), then why is it not likewise useful to have a collection of files, some of which may be null?

List<File> files = new ArrayList<File>();
files.add(null);

Null objects and collections that may contain null objects are both useful. It is really as simple as that.

The statement

File f = null;

is valid and useful (I don't think I need to explain why). It is likewise useful to have a collection of files, some of which may be null.

List<File> files = new ArrayList<File>();
files.add(null);

The usefulness of collections that may contain null objects proceeds directly from the usefulness of objects that may be null. It is really as simple as that.