I have had a quick scan of the Guava API and the new collection types it provides(
Seriously, everything in Guava is useful. I've been using it for quite a while, and am still always discovering something new I can do with it that takes less code than doing it by hand.
Some things others have not really mentioned that I love:
Multimaps are just great. Any time you would use something like
Map<Foo, Collection<Bar>>, use a multimap instead and save yourself a ton of tedious checking for an existing collection mapped to a key and creating and adding it if it isn't there.
Orderingis great for building
Comparators that behave just how you want.
Multimaps.index: these methods take an
Functionand build an
ImmutableListMultimapthat indexes the values in the
Iterableby the result of applying the function to each. So with a function that retrieves the ID of an item, you can index a list of items by their ID in one line.
transform, etc. Despite the verbosity of using classes for
Predicates, I've found this useful. I give an example of one way to make this read nicely here.
ComparisonChainis a small, easily overlooked class that's useful when you want to write a comparison method that compares multiple values in succession and should return when the first difference is found. It removes all the tedium of that, making it just a few lines of chained method calls.
Objects.equal(Object,Object)- null safe equals.
Objects.hashCode(Object...)- easy way to get a hash code based on multiple fields of your class.
Objects.firstNonNull(Object,Object)- reduces the code for getting a default value if the first value is null, especially if the first value is the result of a method call (you'd have to assign it to a variable before doing this the normal way).
CharMatchers were already mentioned, but they're very powerful.
Throwableslets you do some nice things with throwables, such as
Throwables.propagatewhich rethrows a throwable if it's a
Errorand wraps it in a
RuntimeExceptionand throws that otherwise.
I could certainly go on, but I have to get to work. =) Anyway, despite my having listed some things I like here, the fact is that everything in Guava is useful in some situation or another. Much of it is useful very often. As you use it, you'll discover more uses. Not using it will feel a bit like having one hand tied behind your back.