StreamFlex: High-throughput Stream Programming in Java. The stream programming paradigm aims to expose coarse-grained parallelism inapplications that must process continuous sequences of events. The appeal ofstream programming comes from its conceptual simplicity. A program is acollection of independent filters which communicate by the means ofuni-directional data channels. This model lends itself naturally toconcurrent and efficient implementations on modern multiprocessors. As theoutput behavior of filters is determined by the state of their inputchannels, stream programs have fewer opportunities for the errors (such asdata races and deadlocks) that plague shared memory concurrent programming. This paper introduces S<scp>tream</scp>F<scp>lex</scp>, an extension to Java which marries streams with objects and thus enables to combine, in the same Java virtual machine, stream processing code with traditional object-oriented components. S<scp>tream</scp>F<scp>lex</scp> targets high-throughput low-latency applications with stringent quality-of-service requirements. To achieve these goals, it must, at the same time, extend and restrict Java. To allow for program optimization and provide latency guarantees, the S<scp>tream</scp>F<scp>lex</scp> compiler restricts Java by imposing a stricter typing discipline on filters. On the other hand, S<scp>tream</scp>F<scp>lex</scp> extends the Java virtual machine with real-time capabilities, transactional memory and type-safe region-based allocation. The result is a rich and expressive language that can be implemented efficiently.