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feature(using-streams): streams de tipos primitivos
Adicionando exemplos sobre Streams de tipos primitivos: IntStream, DoubleStream e LongStream. Ref. Issue #23
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‎book/05-java-streams/sections/01-using-streams.asc‎

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@@ -432,11 +432,106 @@ Perceba que, mesmo que a operação `peek` esteja antes da operação `limit`, e
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==== Streams primitivos
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. primitivos: DoubleStream, IntStream, LongStream
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. map para primitivos
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. generate para streams primitivos
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. range closed
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. statistics
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Existem Streams específicos para alguns tipos primitivos: `double`, `int` e `long`. Eles possuem a vantagem de evitar Boxing e Unboxing, e também fornecem alguns métodos mais especializados como vamos ver.
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. É possível criar _Streams_ de tipos primitivos com as classes: `DoubleStream`, `IntStream` e `LongStream`.
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[source,java,indent=0]
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.{java-package}/usingstreams/primitives/Streams_Primitives.java
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----
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include::{section-java-package}/usingstreams/primitives/Streams_Primitives.java[tag=code]
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----
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.Saída no console
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[source,console]
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----
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DoubleStream
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1.12.23.3
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IntStream
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123
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123
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LongStream
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123
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123
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----
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. É possível transformar um _Stream_ comum em um _Stream_ de primitivos utilizando as operações `mapTo*`.
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[source,java,indent=0]
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.{java-package}/usingstreams/primitives/Streams_MapTo.java
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----
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include::{section-java-package}/usingstreams/primitives/Streams_MapTo.java[tag=code]
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----
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.Saída no console
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[source,console]
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----
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Stream para IntStream
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1234
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Stream para LongStream
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1234
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Stream para DoubleStream
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1.02.03.04.0
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----
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. É possível gerar Streams infinitos com o método `generate`.
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[source,java,indent=0]
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.{java-package}/usingstreams/primitives/Streams_Generate.java
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----
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include::{section-java-package}/usingstreams/primitives/Streams_Generate.java[tag=code]
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----
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.Saída no console
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[source,console]
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----
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IntStream infinito de números aleatórios
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2111846625
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-1692075394
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122693397
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DoubleStream infinito de números aleatórios
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0.913037010633669
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0.23669861350384735
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0.32655918031847697
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----
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Nesse caso os _Streams_ são realmente infinitos. Só foram apresentados 3 números de cada pois existe a operação `limit`, caso contrário a execução do programa também seria sem fim.
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. É possível utilizar a operação `rangeClosed` ao invés de `range`, deixando o código mais legível.
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[source,java,indent=0]
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.{java-package}/usingstreams/primitives/Streams_RangeClosed.java
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----
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include::{section-java-package}/usingstreams/primitives/Streams_RangeClosed.java[tag=code]
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----
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.Saída no console
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[source,console]
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----
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123
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1234
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----
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Perceba que na chamada utilizando `range`, o último número é exclusivo (não faz parte do _Stream_). No `rangeClosed`, tanto o primeiro quanto o último número são inclusivos (fazem parte do _Stream_).
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. É possível gerar várias estatísticas de _Streams_ utilizando a operação `summaryStatistics`.
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[source,java,indent=0]
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.{java-package}/usingstreams/primitives/Streams_Statistics.java
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----
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include::{section-java-package}/usingstreams/primitives/Streams_Statistics.java[tag=code]
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----
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.Saída no console
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[source,console]
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----
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Quantidade: 10
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Maior: 9
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Menor: 0
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Soma: 45
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Média: 4.5
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----
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==== Collectors
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‎src/org/j6toj8/streams/usingstreams/primitives/Streams_Generate.java‎

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package org.j6toj8.streams.usingstreams.primitives;
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import java.util.Random;
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import java.util.stream.DoubleStream;
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import java.util.stream.IntStream;
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public class Streams_Generate {
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public static void main(String[] args) {
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// tag::code[]
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// Cria Stream infinito de números aleatórios
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System.out.println(" IntStream infinito de números aleatórios");
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IntStream.generate(() -> new Random().nextInt())
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.limit(3)
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.forEach(System.out::println);
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System.out.println("\n DoubleStream infinito de números aleatórios");
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DoubleStream.generate(Math::random)
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.limit(3)
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.forEach(System.out::println);
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// end::code[]
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}
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}

‎src/org/j6toj8/streams/usingstreams/primitives/Streams_MapTo.java‎

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package org.j6toj8.streams.usingstreams.primitives;
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import java.util.Arrays;
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import java.util.List;
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public class Streams_MapTo {
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public static void main(String[] args) {
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// tag::code[]
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List<Integer> list = Arrays.asList(1, 2, 3, 4);
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System.out.println(" Stream para IntStream");
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list.stream() // cria Stream<Integer>
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.mapToInt(Integer::intValue) // transforma em IntStream
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.forEach(System.out::print);
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System.out.println("\n Stream para LongStream");
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list.stream() // cria Stream<Long>
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.mapToLong(Integer::longValue) // transforma em LongStream
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.forEach(System.out::print);
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System.out.println("\n Stream para DoubleStream");
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list.stream() // cria Stream<Double>
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.mapToDouble(Integer::doubleValue) // transforma em DoubleStream
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.forEach(System.out::print);
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// end::code[]
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}
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}

‎src/org/j6toj8/streams/usingstreams/primitives/Streams_Primitives.java‎

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package org.j6toj8.streams.usingstreams.primitives;
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import java.util.stream.DoubleStream;
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import java.util.stream.IntStream;
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import java.util.stream.LongStream;
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public class Streams_Primitives {
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public static void main(String[] args) {
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// tag::code[]
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System.out.println(" DoubleStream");
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DoubleStream.of(1.1, 2.2, 3.3).forEach(System.out::print);
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System.out.println("\n IntStream");
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IntStream.of(1, 2, 3).forEach(System.out::print);
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System.out.println();
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IntStream.range(1, 4).forEach(System.out::print);
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System.out.println("\n LongStream");
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LongStream.of(1, 2, 3).forEach(System.out::print);
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System.out.println("");
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LongStream.range(1, 4).forEach(System.out::print);
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// end::code[]
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}
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}

‎src/org/j6toj8/streams/usingstreams/primitives/Streams_RangeClosed.java‎

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package org.j6toj8.streams.usingstreams.primitives;
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import java.util.stream.IntStream;
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public class Streams_RangeClosed {
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public static void main(String[] args) {
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// tag::code[]
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IntStream.range(1, 4).forEach(System.out::print);
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System.out.println();
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IntStream.rangeClosed(1, 4).forEach(System.out::print);
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// end::code[]
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}
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}

‎src/org/j6toj8/streams/usingstreams/primitives/Streams_Statistics.java‎

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package org.j6toj8.streams.usingstreams.primitives;
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import java.util.IntSummaryStatistics;
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import java.util.stream.IntStream;
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public class Streams_Statistics {
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public static void main(String[] args) {
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// tag::code[]
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IntSummaryStatistics summaryStatistics = IntStream.range(0, 10).summaryStatistics();
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System.out.println("Quantidade: " + summaryStatistics.getCount());
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System.out.println("Maior: " + summaryStatistics.getMax());
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System.out.println("Menor: " + summaryStatistics.getMin());
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System.out.println("Soma: " + summaryStatistics.getSum());
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System.out.println("Média: " + summaryStatistics.getAverage());
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// end::code[]
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}
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}

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