Advanced Collections and Collectors - Java 8 Lambdas - page 81

Figure 5-5. Combiner
You might remember that the last step in our refactoring process, before we got to collectors,
was to put the toString method inline at the end of the method chain. This converted our
StringCombiner into the String that we really wanted ( Figure 5-6 ).
Figure 5-6. Finisher
Our collector's finisher method performs the same purpose. We've already folded our mut-
able container over a Stream of values, but it's not quite the final value that we want. The
finisher gets called here, once, in order to make that conversion. This is especially useful if
we want to create an immutable final value, such as a String , but our container is mutable.
In order to implement the finisher for this operation, we just delegate to the toString
method that we've already written ( Example 5-29 ) .
Example 5-29. A finisher produces the final value returned by the collect operation