Functional Utilities

Simple Function construction and manipulation methods are provided in Functions, including

• forMap(Map<A, B>)
• compose(Function<B, C>, Function<A, B>)
• constant(T)
• identity()
• toStringFunction()

There are considerably more construction and manipulation methods available in Predicates, but a sample includes:

• instanceOf(Class)
• assignableFrom(Class)
• contains(Pattern)
• in(Collection)
• isNull()
• alwaysFalse(), alwaysTrue()
• equalTo(Object)
• compose(Predicate, Function)
• and(Predicate...), or(Predicate...), not(Predicate)

Multiset<Integer> lengths = HashMultiset.create(
  FluentIterable.from(strings)
    .filter(new Predicate<String>() {
       public boolean apply(String string) {
         return CharMatcher.javaUpperCase().matchesAllOf(string);
       }
     })
    .transform(new Function<String, Integer>() {
       public Integer apply(String string) {
         return string.length();
       }
     }));