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feat(collection-improvements): Seção de Java 8 em Collections.
Criação da seção que apresenta exemplos de utilização dos novos métodos do Java 8 para coleções. Ref. Issue #42
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‎book/08-java-collections/sections/05-collection-improvements.asc‎

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:java-package: src/org/j6toj8/collections
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:section-java-package: ../../../{java-package}
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=== Melhorias de Java 8 em Coleções
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.Objetivo
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--------------------------------------------------
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Develop code that uses Java SE 8 collection improvements, including the Collection.removeIf(), List.replaceAll(), Map.computeIfAbsent(), and Map.computeIfPresent() methods
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-
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Desenvolver código que use as melhorias em coleções do Java SE 8, incluindo os métodos Collection.removeIf(), List.replaceAll(), Map.computeIfAbsent(), and Map.computeIfPresent()
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--------------------------------------------------
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O Java 8 trouxe vários métodos em Collections que utilizam como argumento uma função lambda, facilitando algumas operações. Serão apresentados exemplos dos 4 métodos relacionados a esse objetivo.
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. É possível remover um item de uma coleção condicionalmente com uma função lambda.
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[source,java,indent=0]
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.{java-package}/improvements/Collections_RemoveIf.java
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----
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include::{section-java-package}/improvements/Collections_RemoveIf.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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Lista antes do removeIf: [1, 2, 3, 4, 5, 6, 7, 8, 9]
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Lista depois do removeIf: [1, 3, 5, 7, 9]
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----
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. É possível modificar todos os elementos da coleção de acordo com uma operação lambda.
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[source,java,indent=0]
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.{java-package}/improvements/Collections_ReplaceAll.java
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----
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include::{section-java-package}/improvements/Collections_ReplaceAll.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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Lista antes do replaceAll: [1, 2, 3, 4, 5, 6, 7, 8, 9]
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Lista depois do replaceAll: [2, 4, 6, 8, 10, 12, 14, 16, 18]
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----
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. É possível colocar valores em um `Map` a partir de uma função lambda, apenas se a chave *não* estiver presente no `Map`.
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[source,java,indent=0]
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.{java-package}/improvements/Collections_ComputeIfAbsent.java
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----
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include::{section-java-package}/improvements/Collections_ComputeIfAbsent.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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Map antes do computeIfAbsent: {A=65, B=66}
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Map depois do computeIfAbsent: {A=65, B=66, C=67}
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----
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. É possível alterar valores em um `Map` a partir de uma função lambda, apenas se a chave estiver presente no `Map`.
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[source,java,indent=0]
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.{java-package}/improvements/Collections_ComputeIfPresent.java
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----
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include::{section-java-package}/improvements/Collections_ComputeIfPresent.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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Map antes do computeIfAbsent: {A=65, B=66}
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Map depois do computeIfAbsent: {A=4225, B=4356}
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----
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****
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* Using Streams
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Boyarsky, Jeanne; Selikoff, Scott. OCP: Oracle Certified Professional Java SE 8 Programmer II Study Guide (p. 185). Wiley. Edição do Kindle.
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* https://www.baeldung.com/java-8-streams[The Java 8 Stream API Tutorial.]
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****

‎ch08-java-collections.asc‎

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include::book/08-java-collections/sections/01-diamond.asc[]
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include::book/08-java-collections/sections/02-collections-lambda.asc[]
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include::book/08-java-collections/sections/03-data-search.asc[]
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include::book/08-java-collections/sections/04-calculations.asc[]
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include::book/08-java-collections/sections/04-calculations.asc[]
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include::book/08-java-collections/sections/05-collection-improvements.asc[]

‎src/org/j6toj8/collections/improvements/Collections_ComputeIfAbsent.java‎

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package org.j6toj8.collections.improvements;
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import java.util.HashMap;
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public class Collections_ComputeIfAbsent {
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public static void main(String[] args) {
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// tag::code[]
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HashMap<String, Integer> map = new HashMap<String, Integer>();
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map.put("A", "A".hashCode());
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map.put("B", "B".hashCode());
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System.out.println("Map antes do computeIfAbsent: " + map);
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map.computeIfAbsent("A", k -> k.hashCode());
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map.computeIfAbsent("C", k -> k.hashCode());
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System.out.println("Map depois do computeIfAbsent: " + map);
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// end::code[]
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}
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}

‎src/org/j6toj8/collections/improvements/Collections_ComputeIfPresent.java‎

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package org.j6toj8.collections.improvements;
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import java.util.HashMap;
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public class Collections_ComputeIfPresent {
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public static void main(String[] args) {
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// tag::code[]
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HashMap<String, Integer> map = new HashMap<String, Integer>();
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map.put("A", "A".hashCode());
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map.put("B", "B".hashCode());
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System.out.println("Map antes do computeIfAbsent: " + map);
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// k = chave; v = valor
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map.computeIfPresent("A", (k, v) -> k.hashCode() * v);
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map.computeIfPresent("B", (k, v) -> k.hashCode() * v);
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map.computeIfPresent("C", (k, v) -> k.hashCode() * v);
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System.out.println("Map depois do computeIfAbsent: " + map);
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// end::code[]
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}
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}

‎src/org/j6toj8/collections/improvements/Collections_RemoveIf.java‎

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package org.j6toj8.collections.improvements;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.List;
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public class Collections_RemoveIf {
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public static void main(String[] args) {
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// tag::code[]
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List<Integer> list = new ArrayList<Integer>(Arrays.asList(1,2,3,4,5,6,7,8,9));
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System.out.println("Lista antes do removeIf: " + list);
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list.removeIf(n -> n % 2 == 0); // remove números pares
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System.out.println("Lista depois do removeIf: " + list);
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// end::code[]
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}
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}

‎src/org/j6toj8/collections/improvements/Collections_ReplaceAll.java‎

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package org.j6toj8.collections.improvements;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.List;
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public class Collections_ReplaceAll {
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public static void main(String[] args) {
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// tag::code[]
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List<Integer> list = new ArrayList<Integer>(Arrays.asList(1,2,3,4,5,6,7,8,9));
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System.out.println("Lista antes do replaceAll: " + list);
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list.replaceAll(n -> n * 2); // multiplica todos os elementos por 2
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System.out.println("Lista depois do replaceAll: " + list);
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// end::code[]
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}
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}

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