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BAEL-6783: Converting HashMap to an ArrayList in Java (#14814)

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Azhwani 2023-09-24 04:43:53 +02:00 committed by GitHub
parent 8171a4604f
commit 6c4848958f
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5
core-java-modules/core-java-collections-conversions-3/README.md Normal file
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## Java Collections Cookbooks and Examples
This module contains articles about conversions among Collection types in Java.
### Relevant Articles:

26
core-java-modules/core-java-collections-conversions-3/pom.xml Normal file
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<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<artifactId>core-java-collections-conversions-3</artifactId>
<name>core-java-collections-conversions-3</name>
<packaging>jar</packaging>
<parent>
<groupId>com.baeldung.core-java-modules</groupId>
<artifactId>core-java-modules</artifactId>
<version>0.0.1-SNAPSHOT</version>
</parent>
<build>
<finalName>core-java-collections-conversions-3</finalName>
<resources>
<resource>
<directory>src/main/resources</directory>
<filtering>true</filtering>
</resource>
</resources>
</build>
</project>

66
core-java-modules/core-java-collections-conversions-3/src/main/java/com/baeldung/hashmaptoarraylist/HashMapToArrayListConverterUtils.java Normal file
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package com.baeldung.hashmaptoarraylist;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import java.util.stream.Collectors;
import com.google.common.collect.Lists;
import com.google.common.collect.Maps;
import com.google.common.collect.Maps.EntryTransformer;
public class HashMapToArrayListConverterUtils {
static ArrayList<String> convertUsingConstructor(HashMap<Integer, String> hashMap) {
if (hashMap == null) {
return null;
}
return new ArrayList<String>(hashMap.values());
}
static ArrayList<String> convertUsingAddAllMethod(HashMap<Integer, String> hashMap) {
if (hashMap == null) {
return null;
}
ArrayList<String> arrayList = new ArrayList<String>(hashMap.size());
arrayList.addAll(hashMap.values());
return arrayList;
}
static ArrayList<String> convertUsingStreamApi(HashMap<Integer, String> hashMap) {
if (hashMap == null) {
return null;
}
return hashMap.values()
.stream()
.collect(Collectors.toCollection(ArrayList::new));
}
static ArrayList<String> convertUsingForLoop(HashMap<Integer, String> hashMap) {
if (hashMap == null) {
return null;
}
ArrayList<String> arrayList = new ArrayList<String>(hashMap.size());
for (Map.Entry<Integer, String> entry : hashMap.entrySet()) {
arrayList.add(entry.getValue());
}
return arrayList;
}
static public ArrayList<String> convertUsingGuava(HashMap<Integer, String> hashMap) {
if (hashMap == null) {
return null;
}
EntryTransformer<Integer, String, String> entryMapTransformer = (key, value) -> value;
return Lists.newArrayList(Maps.transformEntries(hashMap, entryMapTransformer)
.values());
}
}

60
core-java-modules/core-java-collections-conversions-3/src/test/java/com/baeldung/hashmaptoarraylist/HashMapToArrayListConverterUtilsUnitTest.java Normal file
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package com.baeldung.hashmaptoarraylist;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.containsInAnyOrder;
import java.util.ArrayList;
import java.util.HashMap;
import org.junit.Before;
import org.junit.Test;
public class HashMapToArrayListConverterUtilsUnitTest {
private HashMap<Integer, String> hashMap;
@Before
public void beforeEach() {
hashMap = new HashMap<>();
hashMap.put(1, "AAA");
hashMap.put(2, "BBB");
hashMap.put(3, "CCC");
hashMap.put(4, "DDD");
}
@Test
public void givenAHashMap_whenConvertUsingConstructor_thenReturnArrayList() {
ArrayList<String> myList = HashMapToArrayListConverterUtils.convertUsingConstructor(hashMap);
assertThat(hashMap.values(), containsInAnyOrder(myList.toArray()));
}
@Test
public void givenAHashMap_whenConvertUsingAddAllMethod_thenReturnArrayList() {
ArrayList<String> myList = HashMapToArrayListConverterUtils.convertUsingAddAllMethod(hashMap);
assertThat(hashMap.values(), containsInAnyOrder(myList.toArray()));
}
@Test
public void givenAHashMap_whenConvertUsingForLoop_thenReturnArrayList() {
ArrayList<String> myList = HashMapToArrayListConverterUtils.convertUsingForLoop(hashMap);
assertThat(hashMap.values(), containsInAnyOrder(myList.toArray()));
}
@Test
public void givenAHashMap_whenConvertUsingStreamApi_thenReturnArrayList() {
ArrayList<String> myList = HashMapToArrayListConverterUtils.convertUsingStreamApi(hashMap);
assertThat(hashMap.values(), containsInAnyOrder(myList.toArray()));
}
@Test
public void givenAHashMap_whenConvertUsingGuava_thenReturnArrayList() {
ArrayList<String> myList = HashMapToArrayListConverterUtils.convertUsingGuava(hashMap);
assertThat(hashMap.values(), containsInAnyOrder(myList.toArray()));
}
}