Collection class that doesn’t allow null elements?

Use Constraints:

import com.google.common.collect.Constraints;
...
Constraints.constrainedList(new ArrayList(), Constraints.notNull())

from Guava for maximum flexibility.

UPDATE: Guava Constraints has been deprecated in Release 15 – apparently without replacement.

UPDATE 2: As of now (Guava 19.0-rc2) Constrains is still there and not deprecated anymore. However, it’s missing from the Javadoc.

I’m afraid that the Javadoc is right as MapConstraint have been deprecated in Release 19, too