添加 core-java-collections-conversions 模块
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## Java Collections Cookbooks and Examples
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This module contains articles about conversions among Collection types and arrays in Java.
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### Relevant Articles:
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- [Converting between an Array and a List in Java](https://www.baeldung.com/convert-array-to-list-and-list-to-array)
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- [Converting Between an Array and a Set in Java](https://www.baeldung.com/convert-array-to-set-and-set-to-array)
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- [Convert a Map to an Array, List or Set in Java](https://www.baeldung.com/convert-map-values-to-array-list-set)
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- [Converting a List to String in Java](https://www.baeldung.com/java-list-to-string)
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- [How to Convert List to Map in Java](https://www.baeldung.com/java-list-to-map)
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- [Converting a Collection to ArrayList in Java](https://www.baeldung.com/java-convert-collection-arraylist)
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- [Java 8 Collectors toMap](https://www.baeldung.com/java-collectors-tomap)
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- [Converting Iterable to Collection in Java](https://www.baeldung.com/java-iterable-to-collection)
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- [Converting Iterator to List](https://www.baeldung.com/java-convert-iterator-to-list)
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- More articles: [[next -->]](../core-java-collections-conversions-2)
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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<artifactId>core-java-collections-conversions</artifactId>
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<version>0.1.0-SNAPSHOT</version>
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<name>core-java-collections-conversions</name>
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<packaging>jar</packaging>
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<parent>
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<groupId>com.ossez.core-java-modules</groupId>
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<artifactId>core-java-modules</artifactId>
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<version>0.0.2-SNAPSHOT</version>
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<relativePath>../pom.xml</relativePath>
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</parent>
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<dependencies>
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<dependency>
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<groupId>org.apache.commons</groupId>
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<artifactId>commons-collections4</artifactId>
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<version>${commons-collections4.version}</version>
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</dependency>
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<dependency>
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<groupId>org.apache.commons</groupId>
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<artifactId>commons-lang3</artifactId>
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<version>${commons-lang3.version}</version>
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</dependency>
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</dependencies>
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<build>
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<finalName>core-java-collections-conversions</finalName>
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<resources>
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<resource>
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<directory>src/main/resources</directory>
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<filtering>true</filtering>
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</resource>
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</resources>
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</build>
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</project>
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package com.baeldung.convertToMap;
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public class Book {
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private String name;
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private int releaseYear;
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private String isbn;
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@Override
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public String toString() {
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return "Book{" +
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"name='" + name + '\'' +
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", releaseYear=" + releaseYear +
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", isbn='" + isbn + '\'' +
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'}';
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}
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public String getName() {
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return name;
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}
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public void setName(String name) {
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this.name = name;
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}
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public int getReleaseYear() {
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return releaseYear;
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}
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public void setReleaseYear(int releaseYear) {
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this.releaseYear = releaseYear;
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}
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public String getIsbn() {
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return isbn;
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}
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public void setIsbn(String isbn) {
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this.isbn = isbn;
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}
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public Book(String name, int releaseYear, String isbn) {
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this.name = name;
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this.releaseYear = releaseYear;
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this.isbn = isbn;
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}
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}
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package com.baeldung.convertToMap;
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import java.util.*;
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import java.util.concurrent.ConcurrentHashMap;
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import java.util.function.Function;
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import java.util.stream.Collectors;
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public class ConvertToMap {
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public Map<String, String> listToMap(List<Book> books) {
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return books.stream().collect(Collectors.toMap(Book::getIsbn, Book::getName));
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}
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public Map<Integer, Book> listToMapWithDupKeyError(List<Book> books) {
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return books.stream().collect(Collectors.toMap(Book::getReleaseYear, Function.identity()));
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}
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public Map<Integer, Book> listToMapWithDupKey(List<Book> books) {
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return books.stream().collect(Collectors.toMap(Book::getReleaseYear, Function.identity(), (existing, replacement) -> existing));
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}
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public Map<Integer, Book> listToConcurrentMap(List<Book> books) {
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return books.stream().collect(Collectors.toMap(Book::getReleaseYear, Function.identity(), (o1, o2) -> o1, ConcurrentHashMap::new));
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}
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public TreeMap<String, Book> listToSortedMap(List<Book> books) {
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return books.stream()
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.collect(Collectors.toMap(Book::getName, Function.identity(), (o1, o2) -> o1, TreeMap::new));
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}
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}
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package com.baeldung.convertcollectiontoarraylist;
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/**
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* This POJO is the element type of our collection. It has a deepCopy() method.
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*
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* @author chris
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*/
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public class Foo {
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private int id;
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private String name;
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private Foo parent;
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public Foo() {
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}
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public Foo(int id, String name, Foo parent) {
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this.id = id;
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this.name = name;
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this.parent = parent;
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}
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public int getId() {
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return id;
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}
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public void setId(int id) {
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this.id = id;
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}
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public String getName() {
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return name;
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}
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public void setName(String name) {
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this.name = name;
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}
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public Foo getParent() {
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return parent;
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}
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public void setParent(Foo parent) {
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this.parent = parent;
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}
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public Foo deepCopy() {
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return new Foo(
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this.id, this.name, this.parent != null ? this.parent.deepCopy() : null);
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}
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}
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package com.baeldung.convertlisttomap;
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public class Animal {
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private int id;
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private String name;
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public Animal(int id, String name) {
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this.id = id;
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this.setName(name);
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}
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public int getId() {
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return id;
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}
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public void setId(int id) {
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this.id = id;
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}
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public String getName() {
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return name;
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}
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public void setName(String name) {
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this.name = name;
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}
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}
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package com.baeldung.convertlisttomap;
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import com.google.common.collect.Maps;
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import org.apache.commons.collections4.MapUtils;
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import java.util.HashMap;
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import java.util.List;
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import java.util.Map;
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import java.util.function.Function;
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import java.util.stream.Collectors;
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public class ConvertListToMapService {
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public Map<Integer, Animal> convertListBeforeJava8(List<Animal> list) {
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Map<Integer, Animal> map = new HashMap<>();
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for (Animal animal : list) {
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map.put(animal.getId(), animal);
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}
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return map;
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}
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public Map<Integer, Animal> convertListAfterJava8(List<Animal> list) {
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Map<Integer, Animal> map = list.stream().collect(Collectors.toMap(Animal::getId, Function.identity()));
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return map;
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}
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public Map<Integer, Animal> convertListWithGuava(List<Animal> list) {
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Map<Integer, Animal> map = Maps.uniqueIndex(list, Animal::getId);
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return map;
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}
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public Map<Integer, Animal> convertListWithApacheCommons(List<Animal> list) {
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Map<Integer, Animal> map = new HashMap<>();
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MapUtils.populateMap(map, list, Animal::getId);
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return map;
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}
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}
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<?xml version="1.0" encoding="UTF-8"?>
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<configuration>
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<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
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<encoder>
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<pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
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</pattern>
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</encoder>
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</appender>
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<root level="INFO">
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<appender-ref ref="STDOUT" />
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</root>
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</configuration>
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package com.baeldung.convertToMap;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.Map;
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import java.util.concurrent.ConcurrentHashMap;
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import static org.junit.Assert.*;
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import org.junit.Before;
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import org.junit.Test;
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public class ConvertToMapUnitTest {
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private List<Book> bookList;
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private ConvertToMap convertToMap = new ConvertToMap();
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@Before
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public void init() {
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bookList = new ArrayList<>();
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bookList.add(new Book("The Fellowship of the Ring", 1954, "0395489318"));
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bookList.add(new Book("The Two Towers", 1954, "0345339711"));
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bookList.add(new Book("The Return of the King", 1955, "0618129111"));
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}
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@Test
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public void whenConvertFromListToMap() {
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assertTrue(convertToMap.listToMap(bookList).size() == 3);
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}
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@Test(expected = IllegalStateException.class)
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public void whenMapHasDuplicateKey_without_merge_function_then_runtime_exception() {
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convertToMap.listToMapWithDupKeyError(bookList);
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}
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@Test
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public void whenMapHasDuplicateKeyThenMergeFunctionHandlesCollision() {
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Map<Integer, Book> booksByYear = convertToMap.listToMapWithDupKey(bookList);
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assertEquals(2, booksByYear.size());
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assertEquals("0395489318", booksByYear.get(1954).getIsbn());
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}
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@Test
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public void whenCreateConcurrentHashMap() {
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assertTrue(convertToMap.listToConcurrentMap(bookList) instanceof ConcurrentHashMap);
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}
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@Test
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public void whenMapisSorted() {
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assertTrue(convertToMap.listToSortedMap(bookList).firstKey().equals("The Fellowship of the Ring"));
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}
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}
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package com.baeldung.convertcollectiontoarraylist;
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import java.util.ArrayList;
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import java.util.Collection;
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import java.util.Comparator;
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import java.util.HashSet;
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import java.util.Iterator;
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import static java.util.stream.Collectors.toCollection;
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import org.junit.BeforeClass;
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import org.junit.Test;
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import static org.junit.Assert.*;
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/**
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*
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* @author chris
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*/
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public class CollectionToArrayListUnitTest {
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private static Collection<Foo> srcCollection = new HashSet<>();
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public CollectionToArrayListUnitTest() {
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}
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@BeforeClass
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public static void setUpClass() {
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int i = 0;
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Foo john = new Foo(i++, "John", null);
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Foo mary = new Foo(i++, "Mary", null);
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Foo sam = new Foo(i++, "Sam", john);
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Foo alice = new Foo(i++, "Alice", john);
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Foo buffy = new Foo(i++, "Buffy", sam);
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srcCollection.add(john);
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srcCollection.add(mary);
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srcCollection.add(sam);
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srcCollection.add(alice);
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srcCollection.add(buffy);
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}
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/**
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* Section 3. Using the ArrayList Constructor
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*/
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@Test
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public void whenUsingConstructor_thenVerifyShallowCopy() {
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ArrayList<Foo> newList = new ArrayList<>(srcCollection);
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verifyShallowCopy(srcCollection, newList);
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}
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/**
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* Section 4. Using the Streams API
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*/
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@Test
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public void whenUsingStream_thenVerifyShallowCopy() {
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ArrayList<Foo> newList = srcCollection.stream().collect(toCollection(ArrayList::new));
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verifyShallowCopy(srcCollection, newList);
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}
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/**
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* Section 5. Deep Copy
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*/
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@Test
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public void whenUsingDeepCopy_thenVerifyDeepCopy() {
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ArrayList<Foo> newList = srcCollection.stream()
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.map(Foo::deepCopy)
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.collect(toCollection(ArrayList::new));
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verifyDeepCopy(srcCollection, newList);
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}
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/**
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* Section 6. Controlling the List Order
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*/
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@Test
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public void whenUsingSortedStream_thenVerifySortOrder() {
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ArrayList<Foo> newList = srcCollection.stream()
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.sorted(Comparator.comparing(Foo::getName))
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.collect(toCollection(ArrayList::new));
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assertTrue("ArrayList is not sorted by name", isSorted(newList));
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}
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/**
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* Verify that the contents of the two collections are the same
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* @param a
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* @param b
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*/
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private void verifyShallowCopy(Collection<Foo> a, Collection<Foo> b) {
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assertEquals("Collections have different lengths", a.size(), b.size());
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Iterator<Foo> iterA = a.iterator();
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Iterator<Foo> iterB = b.iterator();
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while (iterA.hasNext()) {
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// test instance identity
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assertSame("Foo instances differ!", iterA.next(), iterB.next());
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}
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}
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/**
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* Verify that the contents of the two collections are the same
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* @param a
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* @param b
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*/
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private void verifyDeepCopy(Collection<Foo> a, Collection<Foo> b) {
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assertEquals("Collections have different lengths", a.size(), b.size());
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Iterator<Foo> iterA = a.iterator();
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Iterator<Foo> iterB = b.iterator();
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while (iterA.hasNext()) {
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Foo nextA = iterA.next();
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Foo nextB = iterB.next();
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// should not be same instance
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assertNotSame("Foo instances are the same!", nextA, nextB);
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// but should have same content
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assertFalse("Foo instances have different content!", fooDiff(nextA, nextB));
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}
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}
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/**
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* Return true if the contents of a and b differ. Test parent recursively
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* @param a
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* @param b
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* @return False if the two items are the same
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*/
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private boolean fooDiff(Foo a, Foo b) {
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if (a != null && b != null) {
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return a.getId() != b.getId()
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|| !a.getName().equals(b.getName())
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|| fooDiff(a.getParent(), b.getParent());
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}
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return !(a == null && b == null);
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}
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/**
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* @param c collection of Foo
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* @return true if the collection is sorted by name
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*/
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private static boolean isSorted(Collection<Foo> c) {
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String prevName = null;
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for (Foo foo : c) {
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if (prevName == null || foo.getName().compareTo(prevName) > 0) {
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prevName = foo.getName();
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} else {
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return false;
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}
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}
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return true;
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}
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}
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package com.baeldung.convertiteratortolist;
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import static org.hamcrest.MatcherAssert.assertThat;
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import static org.hamcrest.collection.IsCollectionWithSize.hasSize;
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import static org.hamcrest.collection.IsIterableContainingInAnyOrder.containsInAnyOrder;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.Iterator;
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import java.util.List;
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import java.util.stream.Collectors;
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import java.util.stream.StreamSupport;
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import org.apache.commons.collections4.IteratorUtils;
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import org.junit.Before;
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import org.junit.Test;
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import com.google.common.collect.ImmutableList;
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import com.google.common.collect.Lists;
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public class ConvertIteratorToListServiceUnitTest {
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Iterator<Integer> iterator;
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@Before
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public void setUp() {
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iterator = Arrays.asList(1, 2, 3)
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.iterator();
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}
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||||
@Test
|
||||
public void givenAnIterator_whenConvertIteratorToListUsingWhileLoop_thenReturnAList() {
|
||||
|
||||
List<Integer> actualList = new ArrayList<>();
|
||||
|
||||
// Convert Iterator to List using while loop dsf
|
||||
while (iterator.hasNext()) {
|
||||
actualList.add(iterator.next());
|
||||
}
|
||||
|
||||
assertThat(actualList, hasSize(3));
|
||||
assertThat(actualList, containsInAnyOrder(1, 2, 3));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenAnIterator_whenConvertIteratorToListAfterJava8_thenReturnAList() {
|
||||
List<Integer> actualList = new ArrayList<>();
|
||||
|
||||
// Convert Iterator to List using Java 8
|
||||
iterator.forEachRemaining(actualList::add);
|
||||
|
||||
assertThat(actualList, hasSize(3));
|
||||
assertThat(actualList, containsInAnyOrder(1, 2, 3));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenAnIterator_whenConvertIteratorToListJava8Stream_thenReturnAList() {
|
||||
|
||||
// Convert iterator to iterable
|
||||
Iterable<Integer> iterable = () -> iterator;
|
||||
|
||||
// Extract List from stream
|
||||
List<Integer> actualList = StreamSupport
|
||||
.stream(iterable.spliterator(), false)
|
||||
.collect(Collectors.toList());
|
||||
|
||||
assertThat(actualList, hasSize(3));
|
||||
assertThat(actualList, containsInAnyOrder(1, 2, 3));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenAnIterator_whenConvertIteratorToImmutableListWithGuava_thenReturnAList() {
|
||||
|
||||
// Convert Iterator to an Immutable list using Guava library in Java
|
||||
List<Integer> actualList = ImmutableList.copyOf(iterator);
|
||||
|
||||
assertThat(actualList, hasSize(3));
|
||||
assertThat(actualList, containsInAnyOrder(1, 2, 3));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenAnIterator_whenConvertIteratorToMutableListWithGuava_thenReturnAList() {
|
||||
|
||||
// Convert Iterator to a mutable list using Guava library in Java
|
||||
List<Integer> actualList = Lists.newArrayList(iterator);
|
||||
|
||||
assertThat(actualList, hasSize(3));
|
||||
assertThat(actualList, containsInAnyOrder(1, 2, 3));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenAnIterator_whenConvertIteratorToMutableListWithApacheCommons_thenReturnAList() {
|
||||
|
||||
// Convert Iterator to a mutable list using Apache Commons library in Java
|
||||
List<Integer> actualList = IteratorUtils.toList(iterator);
|
||||
|
||||
assertThat(actualList, hasSize(3));
|
||||
assertThat(actualList, containsInAnyOrder(1, 2, 3));
|
||||
}
|
||||
}
|
||||
|
|
@ -0,0 +1,68 @@
|
|||
package com.baeldung.convertlisttomap;
|
||||
|
||||
import org.junit.Before;
|
||||
import org.junit.Test;
|
||||
|
||||
import java.util.ArrayList;
|
||||
import java.util.List;
|
||||
import java.util.Map;
|
||||
|
||||
import static org.hamcrest.MatcherAssert.assertThat;
|
||||
import static org.hamcrest.Matchers.containsInAnyOrder;
|
||||
|
||||
public class ConvertListToMapServiceUnitTest {
|
||||
List<Animal> list;
|
||||
|
||||
private ConvertListToMapService convertListService;
|
||||
|
||||
@Before
|
||||
public void init() {
|
||||
this.convertListService = new ConvertListToMapService();
|
||||
this.list = new ArrayList<>();
|
||||
|
||||
Animal cat = new Animal(1, "Cat");
|
||||
list.add(cat);
|
||||
Animal dog = new Animal(2, "Dog");
|
||||
list.add(dog);
|
||||
Animal pig = new Animal(3, "Pig");
|
||||
list.add(pig);
|
||||
Animal cow = new Animal(4, "Cow");
|
||||
list.add(cow);
|
||||
Animal goat = new Animal(5, "Goat");
|
||||
list.add(goat);
|
||||
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenAList_whenConvertBeforeJava8_thenReturnMapWithTheSameElements() {
|
||||
|
||||
Map<Integer, Animal> map = convertListService.convertListBeforeJava8(list);
|
||||
|
||||
assertThat(map.values(), containsInAnyOrder(list.toArray()));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenAList_whenConvertAfterJava8_thenReturnMapWithTheSameElements() {
|
||||
|
||||
Map<Integer, Animal> map = convertListService.convertListAfterJava8(list);
|
||||
|
||||
assertThat(map.values(), containsInAnyOrder(list.toArray()));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenAList_whenConvertWithGuava_thenReturnMapWithTheSameElements() {
|
||||
|
||||
Map<Integer, Animal> map = convertListService.convertListWithGuava(list);
|
||||
|
||||
assertThat(map.values(), containsInAnyOrder(list.toArray()));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenAList_whenConvertWithApacheCommons_thenReturnMapWithTheSameElements() {
|
||||
|
||||
Map<Integer, Animal> map = convertListService.convertListWithApacheCommons(list);
|
||||
|
||||
assertThat(map.values(), containsInAnyOrder(list.toArray()));
|
||||
}
|
||||
|
||||
}
|
||||
|
|
@ -0,0 +1,68 @@
|
|||
package com.baeldung.convertlisttomap;
|
||||
|
||||
import org.junit.Before;
|
||||
import org.junit.Test;
|
||||
|
||||
import java.util.ArrayList;
|
||||
import java.util.List;
|
||||
import java.util.Map;
|
||||
|
||||
import static org.hamcrest.MatcherAssert.assertThat;
|
||||
import static org.hamcrest.Matchers.hasItem;
|
||||
import static org.hamcrest.Matchers.hasSize;
|
||||
|
||||
public class ConvertListWithDuplicatedIdToMapServiceUnitTest {
|
||||
List<Animal> duplicatedIdList;
|
||||
|
||||
private ConvertListToMapService convertListService = new ConvertListToMapService();
|
||||
|
||||
@Before
|
||||
public void init() {
|
||||
|
||||
this.duplicatedIdList = new ArrayList<>();
|
||||
|
||||
Animal cat = new Animal(1, "Cat");
|
||||
duplicatedIdList.add(cat);
|
||||
Animal dog = new Animal(2, "Dog");
|
||||
duplicatedIdList.add(dog);
|
||||
Animal pig = new Animal(3, "Pig");
|
||||
duplicatedIdList.add(pig);
|
||||
Animal cow = new Animal(4, "Cow");
|
||||
duplicatedIdList.add(cow);
|
||||
Animal goat = new Animal(4, "Goat");
|
||||
duplicatedIdList.add(goat);
|
||||
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenADupIdList_whenConvertBeforeJava8_thenReturnMapWithRewrittenElement() {
|
||||
|
||||
Map<Integer, Animal> map = convertListService.convertListBeforeJava8(duplicatedIdList);
|
||||
|
||||
assertThat(map.values(), hasSize(4));
|
||||
assertThat(map.values(), hasItem(duplicatedIdList.get(4)));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void givenADupIdList_whenConvertWithApacheCommons_thenReturnMapWithRewrittenElement() {
|
||||
|
||||
Map<Integer, Animal> map = convertListService.convertListWithApacheCommons(duplicatedIdList);
|
||||
|
||||
assertThat(map.values(), hasSize(4));
|
||||
assertThat(map.values(), hasItem(duplicatedIdList.get(4)));
|
||||
}
|
||||
|
||||
@Test(expected = IllegalStateException.class)
|
||||
public void givenADupIdList_whenConvertAfterJava8_thenException() {
|
||||
|
||||
convertListService.convertListAfterJava8(duplicatedIdList);
|
||||
}
|
||||
|
||||
@Test(expected = IllegalArgumentException.class)
|
||||
public void givenADupIdList_whenConvertWithGuava_thenException() {
|
||||
|
||||
convertListService.convertListWithGuava(duplicatedIdList);
|
||||
|
||||
}
|
||||
|
||||
}
|
||||
|
|
@ -0,0 +1,122 @@
|
|||
package com.baeldung.java.collections;
|
||||
|
||||
import static org.hamcrest.Matchers.contains;
|
||||
import static org.junit.Assert.assertThat;
|
||||
|
||||
import java.util.ArrayList;
|
||||
import java.util.Arrays;
|
||||
import java.util.Iterator;
|
||||
import java.util.List;
|
||||
import java.util.Spliterator;
|
||||
import java.util.Spliterators;
|
||||
import java.util.stream.Collectors;
|
||||
import java.util.stream.StreamSupport;
|
||||
|
||||
import org.apache.commons.collections4.IterableUtils;
|
||||
import org.apache.commons.collections4.IteratorUtils;
|
||||
import org.junit.Test;
|
||||
|
||||
import com.google.common.collect.ImmutableList;
|
||||
import com.google.common.collect.Lists;
|
||||
|
||||
public class IterableToCollectionUnitTest {
|
||||
|
||||
Iterable<String> iterable = Arrays.asList("john", "tom", "jane");
|
||||
Iterator<String> iterator = iterable.iterator();
|
||||
|
||||
@Test
|
||||
public void whenConvertIterableToListUsingJava_thenSuccess() {
|
||||
List<String> result = new ArrayList<String>();
|
||||
for (String str : iterable) {
|
||||
result.add(str);
|
||||
}
|
||||
|
||||
assertThat(result, contains("john", "tom", "jane"));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void whenConvertIterableToListUsingJava8_thenSuccess() {
|
||||
List<String> result = new ArrayList<String>();
|
||||
iterable.forEach(result::add);
|
||||
|
||||
assertThat(result, contains("john", "tom", "jane"));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void whenConvertIterableToListUsingJava8WithSpliterator_thenSuccess() {
|
||||
List<String> result = StreamSupport.stream(iterable.spliterator(), false)
|
||||
.collect(Collectors.toList());
|
||||
|
||||
assertThat(result, contains("john", "tom", "jane"));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void whenConvertIterableToListUsingGuava_thenSuccess() {
|
||||
List<String> result = Lists.newArrayList(iterable);
|
||||
|
||||
assertThat(result, contains("john", "tom", "jane"));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void whenConvertIterableToImmutableListUsingGuava_thenSuccess() {
|
||||
List<String> result = ImmutableList.copyOf(iterable);
|
||||
|
||||
assertThat(result, contains("john", "tom", "jane"));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void whenConvertIterableToListUsingApacheCommons_thenSuccess() {
|
||||
List<String> result = IterableUtils.toList(iterable);
|
||||
|
||||
assertThat(result, contains("john", "tom", "jane"));
|
||||
}
|
||||
|
||||
// ======================== Iterator
|
||||
|
||||
@Test
|
||||
public void whenConvertIteratorToListUsingJava_thenSuccess() {
|
||||
List<String> result = new ArrayList<String>();
|
||||
while (iterator.hasNext()) {
|
||||
result.add(iterator.next());
|
||||
}
|
||||
|
||||
assertThat(result, contains("john", "tom", "jane"));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void whenConvertIteratorToListUsingJava8_thenSuccess() {
|
||||
List<String> result = new ArrayList<String>();
|
||||
iterator.forEachRemaining(result::add);
|
||||
|
||||
assertThat(result, contains("john", "tom", "jane"));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void whenConvertIteratorToListUsingJava8WithSpliterator_thenSuccess() {
|
||||
List<String> result = StreamSupport.stream(Spliterators.spliteratorUnknownSize(iterator, Spliterator.ORDERED), false)
|
||||
.collect(Collectors.toList());
|
||||
|
||||
assertThat(result, contains("john", "tom", "jane"));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void whenConvertIteratorToListUsingGuava_thenSuccess() {
|
||||
List<String> result = Lists.newArrayList(iterator);
|
||||
|
||||
assertThat(result, contains("john", "tom", "jane"));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void whenConvertIteratorToImmutableListUsingGuava_thenSuccess() {
|
||||
List<String> result = ImmutableList.copyOf(iterator);
|
||||
|
||||
assertThat(result, contains("john", "tom", "jane"));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void whenConvertIteratorToListUsingApacheCommons_thenSuccess() {
|
||||
List<String> result = IteratorUtils.toList(iterator);
|
||||
|
||||
assertThat(result, contains("john", "tom", "jane"));
|
||||
}
|
||||
}
|
||||
|
|
@ -0,0 +1,145 @@
|
|||
package com.baeldung.java.collections;
|
||||
|
||||
import java.util.ArrayList;
|
||||
import java.util.Arrays;
|
||||
import java.util.Collection;
|
||||
import java.util.Collections;
|
||||
import java.util.HashMap;
|
||||
import java.util.HashSet;
|
||||
import java.util.List;
|
||||
import java.util.Map;
|
||||
import java.util.Set;
|
||||
|
||||
import org.apache.commons.collections4.CollectionUtils;
|
||||
import org.apache.commons.lang3.ArrayUtils;
|
||||
import org.junit.Test;
|
||||
|
||||
import com.google.common.collect.Lists;
|
||||
import com.google.common.collect.Sets;
|
||||
import com.google.common.primitives.Ints;
|
||||
|
||||
@SuppressWarnings("unused")
|
||||
public class JavaCollectionConversionUnitTest {
|
||||
|
||||
// List -> array; array -> List
|
||||
|
||||
@Test
|
||||
public final void givenUsingCoreJava_whenArrayConvertedToList_thenCorrect() {
|
||||
final Integer[] sourceArray = { 0, 1, 2, 3, 4, 5 };
|
||||
final List<Integer> targetList = Arrays.asList(sourceArray);
|
||||
}
|
||||
|
||||
@Test
|
||||
public final void givenUsingCoreJava_whenListConvertedToArray_thenCorrect() {
|
||||
final List<Integer> sourceList = Arrays.asList(0, 1, 2, 3, 4, 5);
|
||||
final Integer[] targetArray = sourceList.toArray(new Integer[0]);
|
||||
}
|
||||
|
||||
@Test
|
||||
public final void givenUsingGuava_whenArrayConvertedToList_thenCorrect() {
|
||||
final Integer[] sourceArray = { 0, 1, 2, 3, 4, 5 };
|
||||
final List<Integer> targetList = Lists.newArrayList(sourceArray);
|
||||
}
|
||||
|
||||
@Test
|
||||
public final void givenUsingGuava_whenListConvertedToArray_thenCorrect() {
|
||||
final List<Integer> sourceList = Lists.newArrayList(0, 1, 2, 3, 4, 5);
|
||||
final int[] targetArray = Ints.toArray(sourceList);
|
||||
}
|
||||
|
||||
@Test
|
||||
public final void givenUsingCommonsCollections_whenArrayConvertedToList_thenCorrect() {
|
||||
final Integer[] sourceArray = { 0, 1, 2, 3, 4, 5 };
|
||||
final List<Integer> targetList = new ArrayList<>(6);
|
||||
CollectionUtils.addAll(targetList, sourceArray);
|
||||
}
|
||||
|
||||
// Set -> array; array -> Set
|
||||
|
||||
@Test
|
||||
public final void givenUsingCoreJavaV1_whenArrayConvertedToSet_thenCorrect() {
|
||||
final Integer[] sourceArray = { 0, 1, 2, 3, 4, 5 };
|
||||
final Set<Integer> targetSet = new HashSet<Integer>(Arrays.asList(sourceArray));
|
||||
}
|
||||
|
||||
@Test
|
||||
public final void givenUsingCoreJavaV2_whenArrayConvertedToSet_thenCorrect() {
|
||||
final Integer[] sourceArray = { 0, 1, 2, 3, 4, 5 };
|
||||
final Set<Integer> targetSet = new HashSet<Integer>();
|
||||
Collections.addAll(targetSet, sourceArray);
|
||||
}
|
||||
|
||||
@Test
|
||||
public final void givenUsingCoreJava_whenSetConvertedToArray_thenCorrect() {
|
||||
final Set<Integer> sourceSet = Sets.newHashSet(0, 1, 2, 3, 4, 5);
|
||||
final Integer[] targetArray = sourceSet.toArray(new Integer[0]);
|
||||
}
|
||||
|
||||
@Test
|
||||
public final void givenUsingGuava_whenArrayConvertedToSet_thenCorrect() {
|
||||
final Integer[] sourceArray = { 0, 1, 2, 3, 4, 5 };
|
||||
final Set<Integer> targetSet = Sets.newHashSet(sourceArray);
|
||||
}
|
||||
|
||||
@Test
|
||||
public final void givenUsingGuava_whenSetConvertedToArray_thenCorrect() {
|
||||
final Set<Integer> sourceSet = Sets.newHashSet(0, 1, 2, 3, 4, 5);
|
||||
final int[] targetArray = Ints.toArray(sourceSet);
|
||||
}
|
||||
|
||||
@Test
|
||||
public final void givenUsingCommonsCollections_whenArrayConvertedToSet_thenCorrect() {
|
||||
final Integer[] sourceArray = { 0, 1, 2, 3, 4, 5 };
|
||||
final Set<Integer> targetSet = new HashSet<>(6);
|
||||
CollectionUtils.addAll(targetSet, sourceArray);
|
||||
}
|
||||
|
||||
@Test
|
||||
public final void givenUsingCommonsCollections_whenSetConvertedToArrayOfPrimitives_thenCorrect() {
|
||||
final Set<Integer> sourceSet = Sets.newHashSet(0, 1, 2, 3, 4, 5);
|
||||
final Integer[] targetArray = sourceSet.toArray(new Integer[0]);
|
||||
final int[] primitiveTargetArray = ArrayUtils.toPrimitive(targetArray);
|
||||
}
|
||||
|
||||
// Map (values) -> Array, List, Set
|
||||
|
||||
@Test
|
||||
public final void givenUsingCoreJava_whenMapValuesConvertedToArray_thenCorrect() {
|
||||
final Map<Integer, String> sourceMap = createMap();
|
||||
|
||||
final Collection<String> values = sourceMap.values();
|
||||
final String[] targetArray = values.toArray(new String[0]);
|
||||
}
|
||||
|
||||
@Test
|
||||
public final void givenUsingCoreJava_whenMapValuesConvertedToList_thenCorrect() {
|
||||
final Map<Integer, String> sourceMap = createMap();
|
||||
|
||||
final List<String> targetList = new ArrayList<>(sourceMap.values());
|
||||
}
|
||||
|
||||
@Test
|
||||
public final void givenUsingGuava_whenMapValuesConvertedToList_thenCorrect() {
|
||||
final Map<Integer, String> sourceMap = createMap();
|
||||
|
||||
final List<String> targetList = Lists.newArrayList(sourceMap.values());
|
||||
}
|
||||
|
||||
@Test
|
||||
public final void givenUsingCoreJava_whenMapValuesConvertedToSet_thenCorrect() {
|
||||
final Map<Integer, String> sourceMap = createMap();
|
||||
|
||||
final Set<String> targetSet = new HashSet<>(sourceMap.values());
|
||||
}
|
||||
|
||||
// UTIL
|
||||
|
||||
private final Map<Integer, String> createMap() {
|
||||
final Map<Integer, String> sourceMap = new HashMap<>(3);
|
||||
sourceMap.put(0, "zero");
|
||||
sourceMap.put(1, "one");
|
||||
sourceMap.put(2, "two");
|
||||
return sourceMap;
|
||||
}
|
||||
|
||||
}
|
||||
|
|
@ -0,0 +1,31 @@
|
|||
package com.baeldung.java.lists;
|
||||
|
||||
import java.util.Arrays;
|
||||
import java.util.List;
|
||||
import java.util.stream.Collectors;
|
||||
|
||||
import org.apache.commons.lang3.StringUtils;
|
||||
import org.junit.Test;
|
||||
|
||||
public class ListToStringUnitTest {
|
||||
|
||||
@Test
|
||||
public void whenListToString_thenPrintDefault() {
|
||||
List<Integer> intLIst = Arrays.asList(1, 2, 3);
|
||||
System.out.println(intLIst);
|
||||
}
|
||||
|
||||
@Test
|
||||
public void whenCollectorsJoining_thenPrintCustom() {
|
||||
List<Integer> intList = Arrays.asList(1, 2, 3);
|
||||
System.out.println(intList.stream()
|
||||
.map(n -> String.valueOf(n))
|
||||
.collect(Collectors.joining("-", "{", "}")));
|
||||
}
|
||||
|
||||
@Test
|
||||
public void whenStringUtilsJoin_thenPrintCustom() {
|
||||
List<Integer> intList = Arrays.asList(1, 2, 3);
|
||||
System.out.println(StringUtils.join(intList, "|"));
|
||||
}
|
||||
}
|
||||
|
|
@ -24,6 +24,7 @@
|
|||
<module>core-java-collections</module>
|
||||
<module>core-java-collections-2</module>
|
||||
<module>core-java-collections-3</module>
|
||||
<module>core-java-collections-conversions</module>
|
||||
<module>core-java-collections-list</module>
|
||||
<module>core-java-collections-list-2</module>
|
||||
<module>core-java-collections-list-3</module>
|
||||
|
|
|
|||
|
|
@ -1,3 +1,3 @@
|
|||
spring.datasource.url=jdbc:h2:mem:db;DB_CLOSE_DELAY=-1
|
||||
spring.datasource.username=sa
|
||||
spring.datasource.password=sa
|
||||
spring.datasource.password=sa
|
||||
|
|
|
|||
Loading…
Reference in New Issue