? type of Java

For example :

List<? extends HasWord> wordList = toke.tokenize();

? extends HasWord means "A class that extends HasWord." In other words, HasWord itself or any of its children... basically anything that would work with instanceof HasWord.

In more technical terms, ? extends HasWord is a bounded wildcard, covered in Item 28 of Effective Java 2nd Edition, starting on page 134. This is part of the chapter on Generics available online as a PDF.

A question mark is a signifier for 'any type'. ? alone means Any type extending Object (including Object).

Map<String,?>

? is for ? extends Object.