The document discusses Java 8's Stream API, which was presented at the Hanoi JUG in 2015. It provides an overview of key Stream API concepts like intermediate and terminal operations, laziness, and performance tuning. It also discusses how the Stream API changes coding approaches by allowing data to be pipelined and transformed, and provides built-in collectors. Both advantages and disadvantages of the Stream API are presented, such as reducing code size but inability to randomly access streams.

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Java 8: Stream API
Vu Dang Ngoc - eXo

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Introduction to Stream API
1. Stream API at glance
a. Aggregate Operations, Terminal Operations
b. Laziness and performance tuning
2. How Stream API change the way we coding?
3. Advantage and disadvantage
4. Further reading

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Stream example

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Stream API at glance
● Pipeline contain a data source, 1 or many intermediate
operation, 1 terminal operation and linked together by
streams.

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Stream source

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Operations

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Intermediate Operation
● Stream-producing: require a stream and
return another stream
● Always lazy
● Stateless and stateful operations
o Stateless (filter, map …): don’t require information of
other items.
o Stateful (distinct, sorted, limit, peek…): require
information of other items.

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Terminal Operation
● End of pipeline
● Push intermediate operator working
● Short-circuiting: stream don’t have to travel
all data.

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Laziness and performance tuning
● Intermediate operator run only when
Terminate operator asking

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Laziness and performance tuning

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Laziness and performance tuning

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Stream is not loop
continue to next
element
You have no power
here!

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How Stream API change the way we coding?

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How Stream API change the way we coding?

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How Stream API change the way we coding?

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How Stream API change the way we coding?

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How Stream API change the way we coding?
● Terminal operator collect provide many way
to transform data
● Collectors class provide built-in collection
feature.

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How Stream API change the way we coding?

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How Stream API change the way we coding?

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How Stream API change the way we coding?

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How Stream API change the way we coding?

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How Stream API change the way we coding?

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Parallel stream
● Using Fork-Join Pool
● Side-effect
● Some parallel stream operations like reduce
and collect need additional computations
● All sub-tasks should finish in a reasonable
time

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Parallel stream

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Parallel stream

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Parallel stream

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Performance compare

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Performance compare

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Performance compare

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Performance compare

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Performance compare

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Performance compare

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Performance compare

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Performance compare

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Performance compare

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Performance compare

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Performance compare

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Parallel stream performance is unstable

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Advantage and Disadvantage
● The Good
o Reduce size of code
o Easy using parallel computing
o Developer can focus how to process data
o Built-in feature of Collectors class
● The Bad
o No customize operator
o Cannot random access

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Advantage and Disadvantage
● And the Ugly
o Stream cannot reuseable
o Parallel stream performance is unstable and
unpredictable
o Stream don’t store data and cannot modify source
collection.
o Can cause infinite stream

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Infinite stream

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Further reading
● Collection Pipes - article of Martin Fowler
about pipe and filter software pattern
● Java Fork-Join Calamity and Java Parallel
Calamity descript flaws of Fork/Join and
parallel stream
● Active vs Passive iterator
● Parallel Streams and Spliterators

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Referent
● http://www.java2novice.com/java-sorting-
algorithms/quick-sort/
● http://javapapers.com/java/java-stream-api/
● http://winterbe.com/posts/2014/07/31/java8-stream-
tutorial-examples/
● http://www.informit.com/articles/article.aspx?p=2198914
● http://blog.credera.com/technology-insights/java/java-8-
part-1-lamdas-streams-functional-interfaces/
● https://docs.oracle.com/javase/8/docs/api/java/util/strea
m/package-summary.html
● http://java.dzone.com/articles/think-twice-using-java-8
● http://blog.jooq.org/2014/06/13/java-8-friday-10-subtle-
mistakes-when-using-the-streams-api/

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Questions & Answers