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Remove Duplicate Values From HashMap in Java (#14519) 

* Remove Duplicate Values From HashMap in Java

* fix the typo in the package name
This commit is contained in:
Kai Yuan 2023-08-06 19:49:57 +02:00 committed by GitHub
parent fdfc98264d
commit 966d488013
1 changed files with 83 additions and 0 deletions
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core-java-modules/core-java-collections-maps-6/src/test/java/com/baeldung/map/removeduplicate/RemoveDuplicateValuesUnitTest.java Normal file
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@ -0,0 +1,83 @@
package com.baeldung.map.removeuplicate;
import static java.util.stream.Collectors.toMap;
import static org.assertj.core.api.Assertions.assertThat;
import java.util.HashMap;
import java.util.Map;
import org.junit.jupiter.api.Test;
import com.google.common.collect.ImmutableMap;
public class RemoveDuplicateValuesUnitTest {
private Map<String, String> initDevMap() {
Map<String, String> devMap = new HashMap<>();
devMap.put("Tom", "Linux");
devMap.put("Kent", "Linux");
devMap.put("Bob", "MacOS");
devMap.put("Eric", "MacOS");
devMap.put("Peter", "Windows");
devMap.put("Saajan", "Windows");
devMap.put("Jan", "Windows");
devMap.put("Kevin", "FreeBSD");
return devMap;
}
@Test
void whenUsingReverseMap_thenDuplicateValuesAreRemoved() {
Map<String, String> devMap = initDevMap();
Map<String, String> tmpReverseMap = new HashMap<>();
Map<String, String> result = new HashMap<>();
for (String name : devMap.keySet()) {
tmpReverseMap.put(devMap.get(name), name);
}
for (String os : tmpReverseMap.keySet()) {
result.put(tmpReverseMap.get(os), os);
}
assertThat(result.values()).hasSize(4)
.containsExactlyInAnyOrder("Windows", "MacOS", "Linux", "FreeBSD");
}
@Test
void whenUsingStream_thenDuplicateValuesAreRemoved() {
Map<String, String> devMap = initDevMap();
Map<String, String> result = devMap.entrySet()
.stream()
.collect(toMap(Map.Entry::getValue, Map.Entry::getKey, (keyInMap, keyNew) -> keyInMap))
.entrySet()
.stream()
.collect(toMap(Map.Entry::getValue, Map.Entry::getKey));
assertThat(result.values()).hasSize(4)
.containsExactlyInAnyOrder("Windows", "MacOS", "Linux", "FreeBSD");
}
@Test
void whenUsingStream_thenDuplicateValuesAreRemovedAndOnlyLongestNamesExist() {
Map<String, String> devMap = initDevMap();
//@formatter:off
Map<String, String> expected = ImmutableMap.of(
"Eric", "MacOS",
"Kent", "Linux",
"Saajan", "Windows",
"Kevin", "FreeBSD");
//@formatter:on
Map<String, String> result = devMap.entrySet()
.stream()
.collect(toMap(Map.Entry::getValue, Map.Entry::getKey, (k1, k2) -> k1.length() > k2.length() ? k1 : k2))
.entrySet()
.stream()
.collect(toMap(Map.Entry::getValue, Map.Entry::getKey));
assertThat(result).hasSize(4)
.isEqualTo(expected);
}
}