java streams: overview & benefits · 3 learning objectives in this part of the lesson...

Java Streams: Overview & Benefits

Douglas C. [email protected]

www.dre.vanderbilt.edu/~schmidt

Professor of Computer Science

Institute for Software

Integrated Systems

Vanderbilt University

Nashville, Tennessee, USA

mailto:[email protected]

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Learning Objectives in this Part of the Lesson• Understand the structure & functionality

of Java streamsStream source

Aggregate operation (behavior f)

Aggregate operation (behavior g)

Aggregate operation (behavior h)

Input x

Output f(x)

Output g(f(x))

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of Java streams, e.g.,

• Fundamentals of streams

Stream source




Input x

Output f(x)

Output g(f(x))

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of Java streams, e.g.,

• Fundamentals of streams

• Benefits of streams

Stream source




Input x

Output f(x)

Output g(f(x))

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Overview of Java Streams

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• Java streams are a framework firstintroduced into the Java class libraryin Java 8


See docs.oracle.com/javase/tutorial/collections/streams

https://docs.oracle.com/javase/tutorial/collections/streams

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• Java streams are a framework firstintroduced into the Java class libraryin Java 8

• They have continued to evolve a bit in later versions of Java


See www.baeldung.com/java-9-stream-api & blog.codefx.org/java/teeing-collector

http://www.baeldung.com/java-9-stream-api

https://blog.codefx.org/java/teeing-collector/

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• A stream is a pipeline of aggregate operations that process a sequence of elements (aka, “values” or “data”)




Input x

Output f(x)

Output g(f(x))


See docs.oracle.com/javase/tutorial/collections/streams

https://docs.oracle.com/javase/tutorial/collections/streams

9See en.wikipedia.org/wiki/Higher-order_function





Input x

Output f(x)

Output g(f(x))


An aggregate operation is a higher-order function that applies a “behavior”

param to every element in a stream.

https://en.wikipedia.org/wiki/Higher-order_function

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Behavioral parameterization simplifies coping with changing requirements.

See blog.indrek.io/articles/java-8-behavior-parameterization





Input x

Output f(x)

Output g(f(x))


https://blog.indrek.io/articles/java-8-behavior-parameterization/

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Input x

Output f(x)

Output g(f(x))

A stream is conceptually unbounded, though it’s often bounded by practical constraints.


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• We use this stream as a case study example throughout this introduction




See github.com/douglascraigschmidt/LiveLessons/tree/master/Java8/ex12

Input x

Output f(x)

Output g(f(x))

Stream

.of("Ophelia","horatio",

"laertes","Gertrude",

"Hamlet","fortinbras", ...)

.filter(s -> toLowerCase

(s.charAt(0)) == 'h')

.map(this::capitalize)

.sorted()

.forEach(System.out::println);


Print each character in Hamlet that starts with ‘H’ or ‘h’ in consistently capitalized & sorted order.

https://github.com/douglascraigschmidt/LiveLessons/tree/master/Java8/ex12

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Benefits of Java Streams

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• Java streams provide several key benefits to programs & programmers

Benefits of Java Streams…

filter(not(this::urlCached))

collect(toList())

map(this::downloadImage)

flatMap(this::applyFilters)

stream()

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• Java streams provide several key benefits to programs & programmers



collect(toList())



stream()

See github.com/douglascraigschmidt/LiveLessons/tree/master/ImageStreamGang

SocketSocket

List of URLs to Download

…

List of Filters to Apply

Persistent

Data Store

https://github.com/douglascraigschmidt/LiveLessons/tree/master/ImageStreamGang

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• Java streams provide several key benefits to programs & programmers, e.g.

• Concise & readable

• Declarative paradigm focuses on whatfunctions to perform, not how to

perform them



collect(toList())



stream()

See en.wikipedia.org/wiki/Declarative_programming

https://en.wikipedia.org/wiki/Declarative_programming

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• Declarative paradigm focuses on whatfunctions to perform, not how to

perform them



collect(toList())



stream()

e.g., no Java control-flow operations are

applied in this stream

See docs.oracle.com/javase/tutorial/java/nutsandbolts/flow.html

https://docs.oracle.com/javase/tutorial/java/nutsandbolts/flow.html

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• Flexible & composable

• Functions are automatically composed together



collect(toList())



stream()

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• Functions are automatically composed together



collect(toList())



stream()

e.g., the output from filter() is passed as the input to map() etc.

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…


collect(toList())



parallelStream()




• Scalable

• Parallelize performance without the need to write any multi-threaded code


See docs.oracle.com/javase/tutorial/collections/streams/parallelism.html

http://docs.oracle.com/javase/tutorial/collections/streams/parallelism.html

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…


collect(toList())



parallelStream()




• Scalable



See dzone.com/articles/common-fork-join-pool-and-streams

A pool of worker threads is used to process behaviors in parallel

https://dzone.com/articles/common-fork-join-pool-and-streams

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…


collect(toList())



parallelStream()




• Scalable



See gee.cs.oswego.edu/dl/papers/fj.pdf

Data mapped automatically to underlying processor cores

http://gee.cs.oswego.edu/dl/papers/fj.pdf

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End of Java Streams: Overview & Benefits

java streams: overview & benefits · 3 learning objectives in this part of the lesson...

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