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BAEL-8864: Select a Random Key from a HashMap in Java #18254

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BAEL-8864: Select a Random Key from a HashMap in Java #18254

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73 changes: 73 additions & 0 deletions ...e-java-collections-maps-8/src/test/java/com/baeldung/map/randomkey/RandomKeyUnitTest.java
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package com.baeldung.map.randomkey;

import static org.assertj.core.api.Assertions.assertThat;

import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Random;
import java.util.concurrent.ThreadLocalRandom;

import org.junit.jupiter.api.Test;

class RandomKeyUnitTest {

@Test
void givenMap_whenUsingRandomClass_thenGetRandomKey() {
Map<String, String> countries = Map.of("Japan", "Tokyo", "Spain", "Madrid");

List<String> countryNames = new ArrayList<String>(countries.keySet());
int randomIndex = new Random().nextInt(countryNames.size());
String randomCountry = countryNames.get(randomIndex);

assertThat(countries).containsKey(randomCountry);
}

@Test
void givenMap_whenUsingMathRandomMethod_thenGetRandomKey() {
Map<String, String> countries = Map.of("Japan", "Tokyo", "Spain", "Madrid");

List<String> countryNames = new ArrayList<String>(countries.keySet());
int randomIndex = (int) (Math.random() * countryNames.size());
String randomCountry = countryNames.get(randomIndex);

assertThat(countries).containsKey(randomCountry);
}

@Test
void givenMap_whenUsingThreadLocalRandomClass_thenGetRandomKey() {
Map<String, String> countries = Map.of("Japan", "Tokyo", "Spain", "Madrid");

List<String> countryNames = new ArrayList<String>(countries.keySet());
int randomIndex = ThreadLocalRandom.current()
.nextInt(countryNames.size());
String randomCountry = countryNames.get(randomIndex);

assertThat(countries).containsKey(randomCountry);
}

@Test
void givenMap_whenUsingSecureRandomClass_thenGetRandomKey() {
Map<String, String> countries = Map.of("Japan", "Tokyo", "Spain", "Madrid");

List<String> countryNames = new ArrayList<String>(countries.keySet());
int randomIndex = new SecureRandom().nextInt(countryNames.size());
String randomCountry = countryNames.get(randomIndex);

assertThat(countries).containsKey(randomCountry);
}

@Test
void givenMap_whenUsingCollectionsShuffleMethod_thenGetRandomKey() {
Map<String, String> countries = Map.of("Japan", "Tokyo", "Spain", "Madrid");

List<String> countryNames = new ArrayList<String>(countries.keySet());
Collections.shuffle(countryNames);
String randomCountry = countryNames.get(0);

assertThat(countries).containsKey(randomCountry);
}

}