Immutable and Unmodifiable

Immutable

JDK utilities classes can be used to generate immutable empty collections:

Collections.emptyList();
Collections.emptyMap();

Immutable empty collections will reject values.

Unmodifiable

These same classes can be used to wrap standard containers and make them unmodifiable:

Iterables.unmodifiableIterable(samples);
Collections.unmodifiableMap(params);

While it isn't possible modifying this wrapper the original collection may still change.