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Merge branch 'master' into BAEL-3131-Guide-to-Java-HashMap

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Maiklins
2019-09-28 22:52:32 +02:00
committed by GitHub
parent a50e35565b 39e99cd907
commit cbc013cb67
1483 changed files with 9779 additions and 3753 deletions
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8
java-collections-maps-2/README.md
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@@ -2,3 +2,11 @@
- [Map of Primitives in Java](https://www.baeldung.com/java-map-primitives)
- [Copying a HashMap in Java](https://www.baeldung.com/java-copy-hashmap)
- [Guide to Java HashMap]()
- [Guide to WeakHashMap in Java](https://www.baeldung.com/java-weakhashmap)
- [Map to String Conversion in Java](https://www.baeldung.com/java-map-to-string-conversion)
- [Iterate over a Map in Java](https://www.baeldung.com/java-iterate-map)
- [Merging Two Maps with Java 8](https://www.baeldung.com/java-merge-maps)
- [Sort a HashMap in Java](https://www.baeldung.com/java-hashmap-sort)
- [Finding the Highest Value in a Java Map](https://www.baeldung.com/java-find-map-max)
- [Initialize a HashMap in Java](https://www.baeldung.com/java-initialize-hashmap)
- [Java TreeMap vs HashMap](https://www.baeldung.com/java-treemap-vs-hashmap)

19
java-collections-maps-2/pom.xml
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@@ -41,6 +41,22 @@
<artifactId>commons-lang3</artifactId>
<version>${commons-lang3.version}</version>
</dependency>
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-collections4</artifactId>
<version>${commons-collections4.version}</version>
</dependency>
<dependency>
<groupId>one.util</groupId>
<artifactId>streamex</artifactId>
<version>${streamex.version}</version>
</dependency>
<dependency>
<groupId>com.jayway.awaitility</groupId>
<artifactId>awaitility</artifactId>
<version>${avaitility.version}</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.assertj</groupId>
<artifactId>assertj-core</artifactId>
@@ -50,6 +66,9 @@
</dependencies>
<properties>
<streamex.version>0.6.5</streamex.version>
<commons-collections4.version>4.1</commons-collections4.version>
<avaitility.version>1.7.0</avaitility.version>
<eclipse-collections.version>8.2.0</eclipse-collections.version>
<trove4j.version>3.0.2</trove4j.version>
<fastutil.version>8.1.0</fastutil.version>

34
java-collections-maps-2/src/main/java/com/baeldung/map/convert/MapToString.java Normal file
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@@ -0,0 +1,34 @@
package com.baeldung.map.convert;
import com.google.common.base.Joiner;
import org.apache.commons.lang3.StringUtils;
import java.util.Map;
import java.util.stream.Collectors;
public class MapToString {
public static String convertWithIteration(Map<Integer, ?> map) {
StringBuilder mapAsString = new StringBuilder("{");
for (Integer key : map.keySet()) {
mapAsString.append(key + "=" + map.get(key) + ", ");
}
mapAsString.delete(mapAsString.length()-2, mapAsString.length()).append("}");
return mapAsString.toString();
}
public static String convertWithStream(Map<Integer, ?> map) {
String mapAsString = map.keySet().stream()
.map(key -> key + "=" + map.get(key))
.collect(Collectors.joining(", ", "{", "}"));
return mapAsString;
}
public static String convertWithGuava(Map<Integer, ?> map) {
return Joiner.on(",").withKeyValueSeparator("=").join(map);
}
public static String convertWithApache(Map map) {
return StringUtils.join(map);
}
}

21
java-collections-maps-2/src/main/java/com/baeldung/map/convert/StringToMap.java Normal file
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@@ -0,0 +1,21 @@
package com.baeldung.map.convert;
import com.google.common.base.Splitter;
import java.util.Arrays;
import java.util.Map;
import java.util.stream.Collectors;
public class StringToMap {
public static Map<String, String> convertWithStream(String mapAsString) {
Map<String, String> map = Arrays.stream(mapAsString.split(","))
.map(entry -> entry.split("="))
.collect(Collectors.toMap(entry -> entry[0], entry -> entry[1]));
return map;
}
public static Map<String, String> convertWithGuava(String mapAsString) {
return Splitter.on(',').withKeyValueSeparator('=').split(mapAsString);
}
}

6
java-collections-maps-2/src/main/java/com/baeldung/map/CopyHashMap.java → java-collections-maps-2/src/main/java/com/baeldung/map/copyhashmap/CopyHashMap.java
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@@ -1,4 +1,6 @@
package com.baeldung.map;
package com.baeldung.map.copyhashmap;
import org.apache.commons.lang3.SerializationUtils;
import java.util.HashMap;
import java.util.Map;
@@ -6,8 +8,6 @@ import java.util.Map.Entry;
import java.util.Set;
import java.util.stream.Collectors;
import org.apache.commons.lang3.SerializationUtils;
public class CopyHashMap {
public static <String, Employee> HashMap<String, Employee> copyUsingConstructor(HashMap<String, Employee> originalMap) {

80
java-collections-maps-2/src/main/java/com/baeldung/map/initialize/MapInitializer.java Normal file
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@@ -0,0 +1,80 @@
package com.baeldung.map.initialize;
import java.util.AbstractMap;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class MapInitializer {
public static Map<String, String> articleMapOne;
static {
articleMapOne = new HashMap<>();
articleMapOne.put("ar01", "Intro to Map");
articleMapOne.put("ar02", "Some article");
}
public static Map<String, String> createSingletonMap() {
Map<String, String> passwordMap = Collections.singletonMap("username1", "password1");
return passwordMap;
}
public Map<String, String> createEmptyMap() {
Map<String, String> emptyMap = Collections.emptyMap();
return emptyMap;
}
public Map<String, String> createUsingDoubleBrace() {
Map<String, String> doubleBraceMap = new HashMap<String, String>() {
/**
*
*/
private static final long serialVersionUID = 1L;
{
put("key1", "value1");
put("key2", "value2");
}
};
return doubleBraceMap;
}
public Map<String, String> createMapUsingStreamStringArray() {
Map<String, String> map = Stream.of(new String[][] { { "Hello", "World" }, { "John", "Doe" }, })
.collect(Collectors.toMap(data -> data[0], data -> data[1]));
return map;
}
public Map<String, Integer> createMapUsingStreamObjectArray() {
Map<String, Integer> map = Stream.of(new Object[][] { { "data1", 1 }, { "data2", 2 }, })
.collect(Collectors.toMap(data -> (String) data[0], data -> (Integer) data[1]));
return map;
}
public Map<String, Integer> createMapUsingStreamSimpleEntry() {
Map<String, Integer> map = Stream.of(new AbstractMap.SimpleEntry<>("idea", 1), new AbstractMap.SimpleEntry<>("mobile", 2))
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
return map;
}
public Map<String, Integer> createMapUsingStreamSimpleImmutableEntry() {
Map<String, Integer> map = Stream.of(new AbstractMap.SimpleImmutableEntry<>("idea", 1), new AbstractMap.SimpleImmutableEntry<>("mobile", 2))
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
return map;
}
public Map<String, String> createImmutableMapWithStreams() {
Map<String, String> map = Stream.of(new String[][] { { "Hello", "World" }, { "John", "Doe" }, })
.collect(Collectors.collectingAndThen(Collectors.toMap(data -> data[0], data -> data[1]), Collections::<String, String> unmodifiableMap));
return map;
}
}

74
java-collections-maps-2/src/main/java/com/baeldung/map/iteration/MapIteration.java Normal file
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@@ -0,0 +1,74 @@
package com.baeldung.map.iteration;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
public class MapIteration {
public static void main(String[] args) {
MapIteration mapIteration = new MapIteration();
Map<String, Integer> map = new HashMap<>();
map.put("One", 1);
map.put("Three", 3);
map.put("Two", 2);
System.out.println("Iterating Keys of Map Using KeySet");
mapIteration.iterateKeys(map);
System.out.println("Iterating Map Using Entry Set");
mapIteration.iterateUsingEntrySet(map);
System.out.println("Iterating Using Iterator and Map Entry");
mapIteration.iterateUsingIteratorAndEntry(map);
System.out.println("Iterating Using KeySet and For Each");
mapIteration.iterateUsingKeySetAndForeach(map);
System.out.println("Iterating Map Using Lambda Expression");
mapIteration.iterateUsingLambda(map);
System.out.println("Iterating Using Stream API");
mapIteration.iterateUsingStreamAPI(map);
}
public void iterateUsingEntrySet(Map<String, Integer> map) {
for (Map.Entry<String, Integer> entry : map.entrySet()) {
System.out.println(entry.getKey() + ":" + entry.getValue());
}
}
public void iterateUsingLambda(Map<String, Integer> map) {
map.forEach((k, v) -> System.out.println((k + ":" + v)));
}
public void iterateUsingIteratorAndEntry(Map<String, Integer> map) {
Iterator<Map.Entry<String, Integer>> iterator = map.entrySet()
.iterator();
while (iterator.hasNext()) {
Map.Entry<String, Integer> pair = iterator.next();
System.out.println(pair.getKey() + ":" + pair.getValue());
}
}
public void iterateUsingKeySetAndForeach(Map<String, Integer> map) {
for (String key : map.keySet()) {
System.out.println(key + ":" + map.get(key));
}
}
public void iterateUsingStreamAPI(Map<String, Integer> map) {
map.entrySet()
.stream()
.forEach(e -> System.out.println(e.getKey() + ":" + e.getValue()));
}
public void iterateKeys(Map<String, Integer> map) {
for (String key : map.keySet()) {
System.out.println(key);
}
}
}

92
java-collections-maps-2/src/main/java/com/baeldung/map/mapmax/MapMax.java Normal file
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@@ -0,0 +1,92 @@
package com.baeldung.map.mapmax;
import java.util.*;
import java.util.Map.Entry;
public class MapMax {
public <K, V extends Comparable<V>> V maxUsingIteration(Map<K, V> map) {
Map.Entry<K, V> maxEntry = null;
for (Map.Entry<K, V> entry : map.entrySet()) {
if (maxEntry == null || entry.getValue()
.compareTo(maxEntry.getValue()) > 0) {
maxEntry = entry;
}
}
return maxEntry.getValue();
}
public <K, V extends Comparable<V>> V maxUsingCollectionsMax(Map<K, V> map) {
Entry<K, V> maxEntry = Collections.max(map.entrySet(), new Comparator<Entry<K, V>>() {
public int compare(Entry<K, V> e1, Entry<K, V> e2) {
return e1.getValue()
.compareTo(e2.getValue());
}
});
return maxEntry.getValue();
}
public <K, V extends Comparable<V>> V maxUsingCollectionsMaxAndLambda(Map<K, V> map) {
Entry<K, V> maxEntry = Collections.max(map.entrySet(), (Entry<K, V> e1, Entry<K, V> e2) -> e1.getValue()
.compareTo(e2.getValue()));
return maxEntry.getValue();
}
public <K, V extends Comparable<V>> V maxUsingCollectionsMaxAndMethodReference(Map<K, V> map) {
Entry<K, V> maxEntry = Collections.max(map.entrySet(), Comparator.comparing(Map.Entry::getValue));
return maxEntry.getValue();
}
public <K, V extends Comparable<V>> V maxUsingStreamAndLambda(Map<K, V> map) {
Optional<Entry<K, V>> maxEntry = map.entrySet()
.stream()
.max((Entry<K, V> e1, Entry<K, V> e2) -> e1.getValue()
.compareTo(e2.getValue()));
return maxEntry.get()
.getValue();
}
public <K, V extends Comparable<V>> V maxUsingStreamAndMethodReference(Map<K, V> map) {
Optional<Entry<K, V>> maxEntry = map.entrySet()
.stream()
.max(Comparator.comparing(Map.Entry::getValue));
return maxEntry.get()
.getValue();
}
public static void main(String[] args) {
Map<Integer, Integer> map = new HashMap<Integer, Integer>();
map.put(1, 3);
map.put(2, 4);
map.put(3, 5);
map.put(4, 6);
map.put(5, 7);
MapMax mapMax = new MapMax();
System.out.println(mapMax.maxUsingIteration(map));
System.out.println(mapMax.maxUsingCollectionsMax(map));
System.out.println(mapMax.maxUsingCollectionsMaxAndLambda(map));
System.out.println(mapMax.maxUsingCollectionsMaxAndMethodReference(map));
System.out.println(mapMax.maxUsingStreamAndLambda(map));
System.out.println(mapMax.maxUsingStreamAndMethodReference(map));
}
}

60
java-collections-maps-2/src/main/java/com/baeldung/map/mergemaps/Employee.java Normal file
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@@ -0,0 +1,60 @@
package com.baeldung.map.mergemaps;
public class Employee implements Comparable<Employee> {
private Long id;
private String name;
public Employee(Long id, String name) {
this.name = name;
this.id = id;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Employee employee = (Employee) o;
if (!id.equals(employee.id)) return false;
return name.equals(employee.name);
}
@Override
public int hashCode() {
int result = id.hashCode();
result = 31 * result + name.hashCode();
return result;
}
@Override
public String toString() {
return "Employee{" +
"id=" + id +
", name='" + name + '\'' +
'}';
}
@Override
public int compareTo(Employee employee) {
return (int)(this.id - employee.getId());
}
}

105
java-collections-maps-2/src/main/java/com/baeldung/map/mergemaps/MergeMaps.java Normal file
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@@ -0,0 +1,105 @@
package com.baeldung.map.mergemaps;
import one.util.streamex.EntryStream;
import java.util.HashMap;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class MergeMaps {
private static Map<String, Employee> map1 = new HashMap<>();
private static Map<String, Employee> map2 = new HashMap<>();
public static void main(String[] args) {
initialize();
mergeFunction();
streamConcat();
streamOf();
streamEx();
streamMerge();
}
private static void streamMerge() {
Map<String, Employee> map3 = map2.entrySet()
.stream()
.collect(
Collectors.toMap(
Map.Entry::getKey,
Map.Entry::getValue,
(v1, v2) -> new Employee(v1.getId(), v2.getName()),
() -> new HashMap<>(map1)
)
);
System.out.println(map3);
}
private static void streamEx() {
Map<String, Employee> map3 = EntryStream.of(map1)
.append(EntryStream.of(map2))
.toMap((e1, e2) -> e1);
System.out.println(map3);
}
private static void streamOf() {
Map<String, Employee> map3 = Stream.of(map1, map2)
.flatMap(map -> map.entrySet().stream())
.collect(
Collectors.toMap(
Map.Entry::getKey,
Map.Entry::getValue,
(v1, v2) -> new Employee(v1.getId(), v2.getName())
)
);
map3.entrySet().forEach(System.out::println);
}
private static void streamConcat() {
Map<String, Employee> result = Stream.concat(map1.entrySet().stream(), map2.entrySet().stream()).collect(Collectors.toMap(
Map.Entry::getKey,
Map.Entry::getValue,
(value1, value2) -> new Employee(value2.getId(), value1.getName())
));
result.entrySet().forEach(System.out::println);
}
private static void mergeFunction() {
Map<String, Employee> map3 = new HashMap<>(map1);
map2.forEach(
(key, value) -> map3.merge(key, value, (v1, v2) ->
new Employee(v1.getId(), v2.getName()))
);
map3.entrySet().forEach(System.out::println);
}
private static void initialize() {
Employee employee1 = new Employee(1L, "Henry");
map1.put(employee1.getName(), employee1);
Employee employee2 = new Employee(22L, "Annie");
map1.put(employee2.getName(), employee2);
Employee employee3 = new Employee(8L, "John");
map1.put(employee3.getName(), employee3);
Employee employee4 = new Employee(2L, "George");
map2.put(employee4.getName(), employee4);
Employee employee5 = new Employee(3L, "Henry");
map2.put(employee5.getName(), employee5);
}
}

2
java-collections-maps-2/src/main/java/com/baeldung/map/PrimitiveMaps.java → java-collections-maps-2/src/main/java/com/baeldung/map/primitives/PrimitiveMaps.java
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@@ -1,4 +1,4 @@
package com.baeldung.map;
package com.baeldung.map.primitives;
import cern.colt.map.AbstractIntDoubleMap;
import cern.colt.map.OpenIntDoubleHashMap;

104
java-collections-maps-2/src/main/java/com/baeldung/map/sort/SortHashMap.java Normal file
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@@ -0,0 +1,104 @@
package com.baeldung.map.sort;
import com.baeldung.map.mergemaps.Employee;
import com.google.common.base.Functions;
import com.google.common.collect.ImmutableSortedMap;
import com.google.common.collect.Ordering;
import java.util.*;
import java.util.stream.Collectors;
public class SortHashMap {
private static Map<String, Employee> map = new HashMap<>();
public static void main(String[] args) {
initialize();
treeMapSortByKey();
arrayListSortByValue();
arrayListSortByKey();
sortStream();
sortGuava();
addDuplicates();
treeSetByKey();
treeSetByValue();
}
private static void sortGuava() {
final Ordering naturalOrdering =
Ordering.natural().onResultOf(Functions.forMap(map, null));
System.out.println(ImmutableSortedMap.copyOf(map, naturalOrdering));
}
private static void sortStream() {
map.entrySet().stream()
.sorted(Map.Entry.<String, Employee>comparingByKey().reversed())
.forEach(System.out::println);
Map<String, Employee> result = map.entrySet().stream()
.sorted(Map.Entry.comparingByValue())
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,
(oldValue, newValue) -> oldValue, LinkedHashMap::new));
result.entrySet().forEach(System.out::println);
}
private static void treeSetByValue() {
SortedSet<Employee> values = new TreeSet<>(map.values());
System.out.println(values);
}
private static void treeSetByKey() {
SortedSet<String> keysSet = new TreeSet<>(map.keySet());
System.out.println(keysSet);
}
private static void treeMapSortByKey() {
TreeMap<String, Employee> sorted = new TreeMap<>(map);
sorted.putAll(map);
sorted.entrySet().forEach(System.out::println);
}
private static void arrayListSortByValue() {
List<Employee> employeeById = new ArrayList<>(map.values());
Collections.sort(employeeById);
System.out.println(employeeById);
}
private static void arrayListSortByKey() {
List<String> employeeByKey = new ArrayList<>(map.keySet());
Collections.sort(employeeByKey);
System.out.println(employeeByKey);
}
private static void initialize() {
Employee employee1 = new Employee(1L, "Mher");
map.put(employee1.getName(), employee1);
Employee employee2 = new Employee(22L, "Annie");
map.put(employee2.getName(), employee2);
Employee employee3 = new Employee(8L, "John");
map.put(employee3.getName(), employee3);
Employee employee4 = new Employee(2L, "George");
map.put(employee4.getName(), employee4);
}
private static void addDuplicates() {
Employee employee5 = new Employee(1L, "Mher");
map.put(employee5.getName(), employee5);
Employee employee6 = new Employee(22L, "Annie");
map.put(employee6.getName(), employee6);
}
}

48
java-collections-maps-2/src/test/java/com/baeldung/map/convert/MapToStringUnitTest.java Normal file
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@@ -0,0 +1,48 @@
package com.baeldung.map.convert;
import org.apache.commons.collections4.MapUtils;
import org.junit.Assert;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import java.util.HashMap;
import java.util.Map;
public class MapToStringUnitTest {
private Map<Integer, String> wordsByKey = new HashMap<>();
@BeforeEach
public void setup() {
wordsByKey.clear();
wordsByKey.put(1, "one");
wordsByKey.put(2, "two");
wordsByKey.put(3, "three");
wordsByKey.put(4, "four");
}
@Test
public void givenMap_WhenUsingIteration_ThenResultingMapIsCorrect() {
String mapAsString = MapToString.convertWithIteration(wordsByKey);
Assert.assertEquals("{1=one, 2=two, 3=three, 4=four}", mapAsString);
}
@Test
public void givenMap_WhenUsingStream_ThenResultingMapIsCorrect() {
String mapAsString = MapToString.convertWithStream(wordsByKey);
Assert.assertEquals("{1=one, 2=two, 3=three, 4=four}", mapAsString);
}
@Test
public void givenMap_WhenUsingGuava_ThenResultingMapIsCorrect() {
String mapAsString = MapToString.convertWithGuava(wordsByKey);
Assert.assertEquals("1=one,2=two,3=three,4=four", mapAsString);
}
@Test
public void givenMap_WhenUsingApache_ThenResultingMapIsCorrect() {
String mapAsString = MapToString.convertWithApache(wordsByKey);
Assert.assertEquals("{1=one, 2=two, 3=three, 4=four}", mapAsString);
MapUtils.debugPrint(System.out, "Map as String", wordsByKey);
}
}

23
java-collections-maps-2/src/test/java/com/baeldung/map/convert/StringToMapUnitTest.java Normal file
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@@ -0,0 +1,23 @@
package com.baeldung.map.convert;
import org.junit.Assert;
import org.junit.jupiter.api.Test;
import java.util.Map;
public class StringToMapUnitTest {
@Test
public void givenString_WhenUsingStream_ThenResultingStringIsCorrect() {
Map<String, String> wordsByKey = StringToMap.convertWithStream("1=one,2=two,3=three,4=four");
Assert.assertEquals(4, wordsByKey.size());
Assert.assertEquals("one", wordsByKey.get("1"));
}
@Test
void givenString_WhenUsingGuava_ThenResultingStringIsCorrect() {
Map<String, String> wordsByKey = StringToMap.convertWithGuava("1=one,2=two,3=three,4=four");
Assert.assertEquals(4, wordsByKey.size());
Assert.assertEquals("one", wordsByKey.get("1"));
}
}

9
java-collections-maps-2/src/test/java/com/baeldung/map/CopyHashMapUnitTest.java → java-collections-maps-2/src/test/java/com/baeldung/map/copyhashmap/CopyHashMapUnitTest.java
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@@ -1,13 +1,12 @@
package com.baeldung.map;
package com.baeldung.map.copyhashmap;
import static org.assertj.core.api.Assertions.assertThat;
import com.google.common.collect.ImmutableMap;
import org.junit.Test;
import java.util.HashMap;
import java.util.Map;
import org.junit.Test;
import com.google.common.collect.ImmutableMap;
import static org.assertj.core.api.Assertions.assertThat;
public class CopyHashMapUnitTest {

2
java-collections-maps-2/src/test/java/com/baeldung/map/Employee.java → java-collections-maps-2/src/test/java/com/baeldung/map/copyhashmap/Employee.java
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@@ -1,4 +1,4 @@
package com.baeldung.map;
package com.baeldung.map.copyhashmap;
import java.io.Serializable;

27
java-collections-maps-2/src/test/java/com/baeldung/map/initialize/MapInitializerUnitTest.java Normal file
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@@ -0,0 +1,27 @@
package com.baeldung.map.initialize;
import org.junit.Test;
import java.util.Map;
import static org.junit.Assert.assertEquals;
public class MapInitializerUnitTest {
@Test
public void givenStaticMap_whenUpdated_thenCorrect() {
MapInitializer.articleMapOne.put("NewArticle1", "Convert array to List");
assertEquals(MapInitializer.articleMapOne.get("NewArticle1"), "Convert array to List");
}
@Test(expected=UnsupportedOperationException.class)
public void givenSingleTonMap_whenEntriesAdded_throwsException() {
Map<String, String> map = MapInitializer.createSingletonMap();
map.put("username2", "password2");
}
}

58
java-collections-maps-2/src/test/java/com/baeldung/map/mapmax/MapMaxUnitTest.java Normal file
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@@ -0,0 +1,58 @@
package com.baeldung.map.mapmax;
import org.junit.Before;
import org.junit.Test;
import java.util.HashMap;
import java.util.Map;
import static org.junit.Assert.assertEquals;
public class MapMaxUnitTest {
Map<Integer, Integer> map = null;
MapMax mapMax = null;
@Before
public void setupTestData() {
map = new HashMap<Integer, Integer>();
map.put(23, 12);
map.put(46, 24);
map.put(27, 38);
mapMax = new MapMax();
}
@Test
public void givenMap_whenIterated_thenReturnMaxValue() {
assertEquals(new Integer(38), mapMax.maxUsingIteration(map));
}
@Test
public void givenMap_whenUsingCollectionsMax_thenReturnMaxValue() {
assertEquals(new Integer(38), mapMax.maxUsingCollectionsMax(map));
}
@Test
public void givenMap_whenUsingCollectionsMaxAndLambda_thenReturnMaxValue() {
assertEquals(new Integer(38), mapMax.maxUsingCollectionsMaxAndLambda(map));
}
@Test
public void givenMap_whenUsingCollectionsMaxAndMethodReference_thenReturnMaxValue() {
assertEquals(new Integer(38), mapMax.maxUsingCollectionsMaxAndMethodReference(map));
}
@Test
public void givenMap_whenUsingStreamAndLambda_thenReturnMaxValue() {
assertEquals(new Integer(38), mapMax.maxUsingStreamAndLambda(map));
}
@Test
public void givenMap_whenUsingStreamAndMethodReference_thenReturnMaxValue() {
assertEquals(new Integer(38), mapMax.maxUsingStreamAndMethodReference (map));
}
}

58
java-collections-maps-2/src/test/java/com/baeldung/map/treemaphashmap/TreeMapVsHashMapUnitTest.java Normal file
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package com.baeldung.map.treemaphashmap;
import org.hamcrest.Matchers;
import org.junit.Assert;
import org.junit.Test;
import java.util.HashMap;
import java.util.Map;
import java.util.TreeMap;
public class TreeMapVsHashMapUnitTest {
@Test
public void whenInsertObjectsTreeMap_thenNaturalOrder() {
Map<Integer, String> treemap = new TreeMap<>();
treemap.put(3, "TreeMap");
treemap.put(2, "vs");
treemap.put(1, "HashMap");
Assert.assertThat(treemap.keySet(), Matchers.contains(1, 2, 3));
}
@Test(expected = NullPointerException.class)
public void whenInsertNullInTreeMap_thenException() {
Map<Integer, String> treemap = new TreeMap<>();
treemap.put(null, "NullPointerException");
}
@Test
public void whenInsertObjectsHashMap_thenRandomOrder() {
Map<Integer, String> hashmap = new HashMap<>();
hashmap.put(3, "TreeMap");
hashmap.put(2, "vs");
hashmap.put(1, "HashMap");
Assert.assertThat(hashmap.keySet(), Matchers.containsInAnyOrder(1, 2, 3));
}
@Test
public void whenInsertNullInHashMap_thenInsertsNull() {
Map<Integer, String> hashmap = new HashMap<>();
hashmap.put(null, null);
Assert.assertNull(hashmap.get(null));
}
@Test
public void givenHashMapAndTreeMap_whenputDuplicates_thenOnlyUnique() {
Map<Integer, String> treeMap = new HashMap<>();
treeMap.put(1, "Baeldung");
treeMap.put(1, "Baeldung");
Assert.assertTrue(treeMap.size() == 1);
Map<Integer, String> treeMap2 = new TreeMap<>();
treeMap2.put(1, "Baeldung");
treeMap2.put(1, "Baeldung");
Assert.assertTrue(treeMap2.size() == 1);
}
}

72
java-collections-maps-2/src/test/java/com/baeldung/map/weakhashmap/WeakHashMapUnitTest.java Normal file
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package com.baeldung.map.weakhashmap;
import org.junit.Test;
import java.util.WeakHashMap;
import java.util.concurrent.TimeUnit;
import static com.jayway.awaitility.Awaitility.await;
import static org.junit.Assert.assertTrue;
public class WeakHashMapUnitTest {
@Test
public void givenWeakHashMap_whenCacheValueThatHasNoReferenceToIt_GCShouldReclaimThatObject() {
//given
WeakHashMap<UniqueImageName, BigImage> map = new WeakHashMap<>();
BigImage bigImage = new BigImage("image_id");
UniqueImageName imageName = new UniqueImageName("name_of_big_image");
map.put(imageName, bigImage);
assertTrue(map.containsKey(imageName));
//when big image key is not reference anywhere
imageName = null;
System.gc();
//then GC will finally reclaim that object
await().atMost(10, TimeUnit.SECONDS).until(map::isEmpty);
}
@Test
public void givenWeakHashMap_whenCacheValueThatHasNoReferenceToIt_GCShouldReclaimThatObjectButLeaveReferencedObject() {
//given
WeakHashMap<UniqueImageName, BigImage> map = new WeakHashMap<>();
BigImage bigImageFirst = new BigImage("foo");
UniqueImageName imageNameFirst = new UniqueImageName("name_of_big_image");
BigImage bigImageSecond = new BigImage("foo_2");
UniqueImageName imageNameSecond = new UniqueImageName("name_of_big_image_2");
map.put(imageNameFirst, bigImageFirst);
map.put(imageNameSecond, bigImageSecond);
assertTrue(map.containsKey(imageNameFirst));
assertTrue(map.containsKey(imageNameSecond));
//when
imageNameFirst = null;
System.gc();
//then
await().atMost(10, TimeUnit.SECONDS).until(() -> map.size() == 1);
await().atMost(10, TimeUnit.SECONDS).until(() -> map.containsKey(imageNameSecond));
}
class BigImage {
public final String imageId;
BigImage(String imageId) {
this.imageId = imageId;
}
}
class UniqueImageName {
public final String imageName;
UniqueImageName(String imageName) {
this.imageName = imageName;
}
}
}