Lambda-Enabled Concurrency - Java 8 Lambdas - page 167

threads to be spawned simultaneously. This results in too many locks in contention and too
much context switching. If you want to deal with thousands of concurrent connections or
more, it's usually better to go nonblocking.

Key Points
▪ Event-driven architectures are easy to implement using lambda-based callbacks.

▪ A CompletableFuture represents an IOU for a value. They can be easily composed and
combined using lambdas.

▪ An Observable extends the idea of a CompletableFuture to streams of data.

Exercises

There's really only one exercise for this chapter, and it requires refactoring some code to use
a CompletableFuture . We'll start out with the BlockingArtistAnalyzer class shown in
Example 9-18 . This class takes the names of two artists, looks up the Artist objects from
the names, and returns true if the first artist has more members and false otherwise. It is
injected with an artistLookupService that may take some time to look up the Artist in
question. Because BlockingArtistAnalyzer blocks on this service twice sequentially, the
analyzer can be slow; the goal of our exercise is to speed it up.

Example 9-18. The BlockingArtistAnalyzer tells its clients which Artist has more members
public public class class BlockingArtistAnalyzer BlockingArtistAnalyzer {

private private final final Function < String , Artist > artistLookupService ;

public public BlockingArtistAnalyzer ( Function < String , Artist > artistLookupService ) {

this

this . artistLookupService = artistLookupService ;

}

public public boolean boolean isLargerGroup ( String artistName , String otherArtistName ) {

return return getNumberOfMembers ( artistName ) > getNumberOfMembers ( otherArtistName );

}

private private long long getNumberOfMembers ( String artistName ) {

return

return artistLookupService . apply ( artistName )
. getMembers ()