Class names from java.lang should never be reused. From Java Puzzlers:

Avoid reusing the names of platform classes, and never reuse class names from java.lang, because these names are automatically imported everywhere. Programmers are used to seeing these names in their unqualified form and naturally assume that these names refer to the familiar classes from java.lang. If you reuse one of these names, the unqualified name will refer to the new definition any time it is used inside its own package.