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Learn How to Implement Java Sequential

SearchStreamGang Hook Methods

Douglas C. Schmidt

[email protected]

www.dre.vanderbilt.edu/~schmidt

Professor of Computer Science

Institute for Software

Integrated Systems

Vanderbilt University

Nashville, Tennessee, USA

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2

Learning Objectives in this Part of the Lesson

•

Know how to apply sequential streams to the SearchStreamGang program

•

Understand the SearchStreamGang process

Stream() & processInput() hook methods

Starting SearchStreamGangTest

PARALLEL_SPLITERATOR executed in 409 msecs

COMPLETABLE_FUTURES_INPUTS executed in 426 msecs COMPLETABLE_FUTURES_PHASES executed in 427 msecs PARALLEL_STREAMS executed in 437 msecs

PARALLEL_STREAM_PHASES executed in 440 msecs RXJAVA_PHASES executed in 485 msecs

PARALLEL_STREAM_INPUTS executed in 802 msecs RXJAVA_INPUTS executed in 866 msecs

SEQUENTIAL_LOOPS executed in 1638 msecs

SEQUENTIAL_STREAM executed in 1958 msecs

Ending SearchStreamGangTest map(phrase -> searchForPhrase(…)) filter(not(SearchResults::isEmpty)) collect(toList()) 45,000+ phrases Search Phrases stream()

(3)

3

Implementing

processStream() as a

Sequential Stream

(4)

4

•

processStream

() sequentially searches for phrases in lists of input “strings”

Implementing processStream() as a Sequential Stream

… Stream<List <SearchResults>> Stream <CharSequence> List<List <SearchResults>> … List <CharSequence> … map(this::processInput) collect(toList())

Input Strings to Search

…

stream() Complete works of Shakespeare

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5

•

processStream

() sequentially searches for phrases in lists of input “strings”

protected List<List<SearchResults>> processStream() { List<CharSequence> inputList = getInput();

return inputList .stream()

.map(this::processInput) .collect(toList());

}

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6

•

processStream

() sequentially searches for phrases in lists of input “strings”

protected List<List<SearchResults>> processStream() {

List<CharSequence> inputList = getInput();

return inputList .stream()

.map(this::processInput) .collect(toList());

}

Implementing processStream() as a Sequential Stream

Get list of strings containing all works of Shakespeare

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7

•

processStream

() sequentially searches for phrases in lists of input “strings”

protected List<List<SearchResults>> processStream() {

List<CharSequence> inputList = getInput();

return inputList .stream()

.map(this::processInput) .collect(toList());

}

Implementing processStream() as a Sequential Stream

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8

•

processStream

() sequentially searches for phrases in lists of input “strings”

protected List<List<SearchResults>> processStream() {

List<CharSequence> inputList = getInput();

return inputList .stream()

.map(this::processInput) .collect(toList());

}

Implementing processStream() as a Sequential Stream

CharSequence optimizes subSequence() to avoid memory copies (cf. String substring())

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9

•

processStream

() sequentially searches for phrases in lists of input “strings”

protected List<List<SearchResults>> processStream() { List<CharSequence> inputList = getInput();

return inputList .stream()

.map(this::processInput) .collect(toList());

}

Implementing processStream() as a Sequential Stream

Returns a list of lists of search results denoting how many times a search phrase appeared in each input string

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10

See “

Java Sequential SearchStreamGang Example: Implementing printPhrases()

”

•

processStream

() sequentially searches for phrases in lists of input “strings”

protected List<List<SearchResults>> processStream() { List<CharSequence> inputList = getInput();

return inputList .stream()

.map(this::processInput) .collect(toList());

}

Implementing processStream() as a Sequential Stream

We’ll later show how flatMap() “flattens” List<List

(11)

11

•

processStream

() sequentially searches for phrases in lists of input “strings”

protected List<List<SearchResults>> processStream() { List<CharSequence> inputList = getInput();

return inputList .stream()

.map(this::processInput) .collect(toList());

}

Implementing processStream() as a Sequential Stream

Stores # of times a phrase appeared in an input string

(12)

12

•

processStream

() sequentially searches for phrases in lists of input “strings”

protected List<List<SearchResults>> processStream() { List<CharSequence> inputList = getInput();

return inputList

.stream()

.map(this::processInput)

.collect(toList());

}

Implementing processStream() as a Sequential Stream

processStream() is implemented via a sequential stream pipeline

(13)

13

•

processStream

() sequentially searches for phrases in lists of input “strings”

protected List<List<SearchResults>> processStream() { List<CharSequence> inputList = getInput();

return inputList

.stream()

.map(this::processInput) .collect(toList());

}

Implementing processStream() as a Sequential Stream

This factory method converts the input list into a stream

(14)

14

•

processStream

() sequentially searches for phrases in lists of input “strings”

protected List<List<SearchResults>> processStream() { List<CharSequence> inputList = getInput();

return inputList .stream()

.map(this::processInput)

.collect(toList()); }

Implementing processStream() as a Sequential Stream

(15)

15

•

processStream

() sequentially searches for phrases in lists of input “strings”

protected List<List<SearchResults>> processStream() { List<CharSequence> inputList = getInput();

return inputList .stream()

.map(this::processInput)

.collect(toList()); }

Implementing processStream() as a Sequential Stream

(16)

16

•

processStream

() sequentially searches for phrases in lists of input “strings”

protected List<List<SearchResults>> processStream() { List<CharSequence> inputList = getInput();

return inputList .stream()

.map(this::processInput)

.collect(toList());

}

Implementing processStream() as a Sequential Stream

(17)

17

•

processStream

() sequentially searches for phrases in lists of input “strings”

protected List<List<SearchResults>> processStream() { List<CharSequence> inputList = getInput();

return inputList .stream()

.map(this::processInput)

.collect(toList());

}

Implementing processStream() as a Sequential Stream

(18)

18

•

processStream

() sequentially searches for phrases in lists of input “strings”

protected List<List<SearchResults>> processStream() { List<CharSequence> inputList = getInput();

return inputList .stream()

.map(this::processInput)

.collect(toList());

}

Implementing processStream() as a Sequential Stream

toList() allocate memory for results, which is less error-prone than the OO version!

(19)

19

•

processStream

() sequentially searches for phrases in lists of input “strings”

protected List<List<SearchResults>> processStream() { List<CharSequence> inputList = getInput();

return inputList

.stream()

.map(this::processInput) .collect(toList());

}

Implementing processStream() as a Sequential Stream

Return a list of lists of search results denoting how many times a search phrase appeared in each input string

(20)

20

Implementing

processInput() as a

Sequential Stream

(21)

21

•

processInput() searches an input string for all occurrences of phrases to find

Implementing processInput() as a Sequential Stream

… Stream <SearchResults> Stream <String> List <SearchResults> … List <String> … map(phrase -> searchForPhrase(…)) filter(not(SearchResults::isEmpty)) collect(toList()) 45,000+ phrases Search Phrases stream() Stream <SearchResults>

(22)

22

•

processInput() searches an input string for all occurrences of phrases to find

List<SearchResults> processInput(CharSequence inputSeq) {

String title = getTitle(inputSeq);

CharSequence input = inputSeq.subSequence(...);

List<SearchResults> results = mPhrasesToFind .stream()

.map(phrase

-> searchForPhrase(phrase, input, title, false)) .filter(not(SearchResults::isEmpty))

.collect(toList()); return results;

}

(23)

23

•

processInput() searches an input string for all occurrences of phrases to find

List<SearchResults> processInput(CharSequence inputSeq) {

String title = getTitle(inputSeq);

CharSequence input = inputSeq.subSequence(...);

List<SearchResults> results = mPhrasesToFind .stream()

.map(phrase

-> searchForPhrase(phrase, input, title, false)) .filter(not(SearchResults::isEmpty))

.collect(toList()); return results;

}

Implementing processInput() as a Sequential Stream

The inputSeq is a section of a text file managed by the test driver program

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24

•

processInput() searches an input string for all occurrences of phrases to find

List<SearchResults> processInput(CharSequence inputSeq) {

String title = getTitle(inputSeq);

CharSequence input = inputSeq.subSequence(...);

List<SearchResults> results = mPhrasesToFind .stream()

.map(phrase

-> searchForPhrase(phrase, input, title, false)) .filter(not(SearchResults::isEmpty))

.collect(toList()); return results;

}

Implementing processInput() as a Sequential Stream

(25)

25

•

processInput() searches an input string for all occurrences of phrases to find

List<SearchResults> processInput(CharSequence inputSeq) { String title = getTitle(inputSeq);

CharSequence input = inputSeq.subSequence(...);

List<SearchResults> results = mPhrasesToFind .stream()

.map(phrase

-> searchForPhrase(phrase, input, title, false)) .filter(not(SearchResults::isEmpty))

.collect(toList()); return results;

}

Implementing processInput() as a Sequential Stream

subSequence() is used to avoid memory copying overhead for substrings

(26)

26

•

processInput() searches an input string for all occurrences of phrases to find

List<SearchResults> processInput(CharSequence inputSeq) { String title = getTitle(inputSeq);

CharSequence input = inputSeq.subSequence(...);

List<SearchResults> results = mPhrasesToFind

.stream()

.map(phrase

-> searchForPhrase(phrase, input, title, false)) .filter(not(SearchResults::isEmpty))

.collect(toList()); return results;

}

Convert a list of phrases into a stream

(27)

27

•

processInput() searches an input string for all occurrences of phrases to find

List<SearchResults> processInput(CharSequence inputSeq) { String title = getTitle(inputSeq);

CharSequence input = inputSeq.subSequence(...);

List<SearchResults> results = mPhrasesToFind .stream()

.map(phrase

-> searchForPhrase(phrase, input, title, false))

.filter(not(SearchResults::isEmpty)) .collect(toList());

return results; }

Implementing processInput() as a Sequential Stream

Apply this function lambda to all phrases in input stream & return an output stream of SearchResults

(28)

28

•

processInput() searches an input string for all occurrences of phrases to find

List<SearchResults> processInput(CharSequence inputSeq) { String title = getTitle(inputSeq);

CharSequence input = inputSeq.subSequence(...);

List<SearchResults> results = mPhrasesToFind .stream()

.map(phrase

-> searchForPhrase(phrase, input, title, false))

.filter(not(SearchResults::isEmpty))

.collect(toList()); return results;

}

Implementing processInput() as a Sequential Stream

Returns output stream containing non-empty SearchResults from input stream

(29)

29

•

processInput() searches an input string for all occurrences of phrases to find

List<SearchResults> processInput(CharSequence inputSeq) { String title = getTitle(inputSeq);

CharSequence input = inputSeq.subSequence(...);

List<SearchResults> results = mPhrasesToFind .stream()

.map(phrase

-> searchForPhrase(phrase, input, title, false))

.filter(not(SearchResults::isEmpty))

.collect(toList()); return results;

}

Implementing processInput() as a Sequential Stream

This approach uses a method reference along with a negator predicate lambda

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30

•

processInput() searches an input string for all occurrences of phrases to find

List<SearchResults> processInput(CharSequence inputSeq) { String title = getTitle(inputSeq);

CharSequence input = inputSeq.subSequence(...);

List<SearchResults> results = mPhrasesToFind .stream()

.map(phrase

-> searchForPhrase(phrase, input, title, false)) .filter(((Predicate<String>) SearchResults::isEmpty))

.negate())

.collect(toList()); return results;

}

Implementing processInput() as a Sequential Stream

See docs.oracle.com/javase/8/docs/api/java/util/function/Predicate.html#negate

Another approach uses a composed predicate

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31

Implementing processInput() as a Sequential Stream

•

processInput() searches an input string for all occurrences of phrases to find

List<SearchResults> processInput(CharSequence inputSeq) { String title = getTitle(inputSeq);

CharSequence input = inputSeq.subSequence(...);

List<SearchResults> results = mPhrasesToFind .stream()

.map(phrase

-> searchForPhrase(phrase, input, title, false))

.filter(result -> result.size() > 0)

.collect(toList()); return results;

}

Yet another approach uses a lambda expression

(32)

32

•

processInput() searches an input string for all occurrences of phrases to find

List<SearchResults> processInput(CharSequence inputSeq) { String title = getTitle(inputSeq);

CharSequence input = inputSeq.subSequence(...);

List<SearchResults> results = mPhrasesToFind .stream()

.map(phrase

-> searchForPhrase(phrase, input, title, false))

.filter(not(SearchResults::isEmpty))

.collect(toList()); return results;

}

These are both intermediate operations

Implementing processInput() as a Sequential Stream

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33

Implementing processInput() as a Sequential Stream

•

processInput() searches an input string for all occurrences of phrases to find

List<SearchResults> processInput(CharSequence inputSeq) { String title = getTitle(inputSeq);

CharSequence input = inputSeq.subSequence(...);

List<SearchResults> results = mPhrasesToFind .stream()

.map(phrase

-> searchForPhrase(phrase, input, title, false)) .filter(not(SearchResults::isEmpty))

.collect(toList());

return results; }

This terminal operation triggers intermediate operation processing & yields a list result

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34

Implementing processInput() as a Sequential Stream

•

processInput() searches an input string for all occurrences of phrases to find

List<SearchResults> processInput(CharSequence inputSeq) { String title = getTitle(inputSeq);

CharSequence input = inputSeq.subSequence(...);

List<SearchResults> results = mPhrasesToFind

.stream() .map(phrase

-> searchForPhrase(phrase, input, title, false)) .filter(not(SearchResults::isEmpty))

.collect(toList()); return results;

}

This terminal operation triggers intermediate operation processing & yields a list result

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35

•

processInput() searches an input string for all occurrences of phrases to find

List<SearchResults> processInput(CharSequence inputSeq) { String title = getTitle(inputSeq);

CharSequence input = inputSeq.subSequence(...);

List<SearchResults> results = mPhrasesToFind .stream()

.map(phrase

-> searchForPhrase(phrase, input, title, false)) .filter(not(SearchResults::isEmpty))

.collect(toList());

return results;

}

The list result is returned back to the map() operation in processStream()

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End of Learn How to

Implement Java Sequential

SearchStreamGang Hook

See www.javaspecialists.eu/archive/Issue230.html See livelessons/utils/SearchResults.java SearchStreamGang/src/main/java/livelessons/utils/SharedString.java ee SearchStreamGang/src/main/java/livelessons/utils/StreamsUtils.java ee docs.oracle.com/javase/8/docs/api/java/util/function/Predicate.html#negate

References

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