java8 training - class 3

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Java8 Training – Class 3

-Marut SinghEmail: singh.marut@gmail.com

https://github.com/singhmarut/java8traininghttp://www.Marutsingh.com

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Stream Operations Intermediate

Lazy Always create a new stream Stateless (filter, map) Stateful (distinct,sorted)

Terminal

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Stream Operations

forEachRandom random = new Random(); random.ints().limit(10).forEach(System.out::println);

mapList<Integer> numbers = Arrays.asList(3, 2, 2, 3, 7, 3, 5); //get list of unique squares List<Integer> squaresList = numbers.stream().map( i -> i*i).distinct().collect(Collectors.toList());

filterList<String>strings = Arrays.asList("abc", "", "bc", "efg", "abcd","", "jkl");//get count of empty string int count = strings.stream().filter(string -> string.isEmpty()).count();

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Stream operations sorted

Random random = new Random(); random.ints().limit(10).sorted().forEach(System.out::println);

Distinct Parallel Processing

List<String> strings = Arrays.asList("abc", "", "bc", "efg", "abcd","", "jkl"); //get count of empty string int count = strings.parallelStream().filter(string -> string.isEmpty()).count();

CollectorsList<String>strings = Arrays.asList("abc", "", "bc", "efg", "abcd","", "jkl"); List<String> filtered = strings.stream().filter(string -> !string.isEmpty()).collect(Collectors.toList()); System.out.println("Filtered List: " + filtered); String mergedString = strings.stream().filter(string -> !string.isEmpty()).collect(Collectors.joining(", ")); System.out.println("Merged String: " + mergedString);

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Statistics

Arrays.asList(3, 2, 2, 3, 7, 3, 5) .stream().mapToInt((x) -> x).getMax();

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Optional Class

Avoid NullPointerException Optional.empty() Optional.of(Class<T>) Optional.ofNullable(Class<T>)

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Lazy Processing

By default all intermediate operations are lazy They all return Stream<T>

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Sorting a stream

new Random().ints().limit(10).sorted().forEach(rand -> System.out.println(rand));

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Stream operations

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Parallel Streams

behavioral parameters in stream pipelines whose source might not be concurrent should never modify the stream's data source. 

A behavioral parameter is said to interfere with a non-concurrent data source if it modifies, or causes to be modified, the stream's data source.

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New DateTime API

Problems with old date time api (java.util.date) Not thread safe  Inconsistent design

Default Date starts from 1900 (month starts from 1, and day starts from 0) Difficult time zone handling

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Java.time

Classes Local − Simplified date-time API with no complexity of timezone handling via

static methods LocalDate LocalTime LocalDateTime Instant (Instant is an instantaneous point on the global time-line (UTC), and is

unrelated to time-zone)

Zoned - Specialized date-time API to deal with various timezones. Periods - deal with date based amount of time. Duration - deal with time based amount of time.

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Java.time

ZoneId ireland = ZoneId.ofOffset("GMT", ZoneOffset.ofHours(+3));

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File NIO

Main Differences Betwen Java NIO and IO

IO NIOStream oriented Buffer orientedBlocking IO Non blocking IO  Selectors