[grdvnl]

The Optional<T> in Guava just forces one to explicitly check for null and then get the container object during development. A typical pattern would be:

Given an object a of type Optional<MyObject>, we write:

if (a.isPresent()){ MyObject o = a.get() }

Of course, I could still do a.get() without evaluating isPresent() and end up with an java.lang.IllegalStateException. Here, we are "reminded" to do the null check.

[mercurial]

You can force Maybe in Haskell, and get a bad surprise at runtime as well.