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BAEL-9382: Stable Values in Java 25 #18796

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Sep 21, 2025
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BAEL-9382: Stable Values in Java 25 #18796

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5bc457e
Stable Values in Java 25: Sample
danielmcnally285 Sep 2, 2025
119865d
Remove final From Local Variables
jzheaux Sep 21, 2025
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28 changes: 28 additions & 0 deletions core-java-modules/core-java-25/pom.xml
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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-25</artifactId>

<parent>
<groupId>com.baeldung.core-java-modules</groupId>
<artifactId>core-java-modules</artifactId>
<version>0.0.1-SNAPSHOT</version>
</parent>

<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>25</source>
<target>25</target>
<compilerArgs>--enable-preview</compilerArgs>
</configuration>
</plugin>
</plugins>
</build>

</project>
78 changes: 78 additions & 0 deletions ...va-modules/core-java-25/src/test/java/com/baeldung/stablevalues/StableValuesUnitTest.java
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package com.baeldung.stablevalues;

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

import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.function.Function;

import org.junit.jupiter.api.BeforeEach

class StableValuesUnitTest {

private Set<String> cities;

private String expensiveMethodToDetermineCountry(String city) {
switch(city) {
case "Berlin":
return "Germany";
case "London":
return "England";
case "Madrid":
return "Spain";
case "Paris":
return "France";
default:
throw new RuntimeException("Unsupported city");
}
}

@Test
void givenStableFunctionForCityToCountry_whenValidInputsUsed_thenVerifyFunctionResultsAreExpected() {
Function<String, String> cityToCountry = StableValue.function(cities, city -> expensiveMethodToDetermineCountry(city));

assertThat(cityToCountry.apply("London")).isEqualTo("England");
assertThat(cityToCountry.apply("Madrid")).isEqualTo("Spain");
assertThat(cityToCountry.apply("Paris")).isEqualTo("France");
}

@Test
void givenStableFunctionForCityToCountry_whenInvalidInputUsed_thenExceptionThrown() {
Function<String, String> cityToCountry = StableValue.function(cities, city -> expensiveMethodToDetermineCountry(city));

assertThatIllegalArgumentException().isThrownBy(() -> cityToCountry.apply("Berlin"));
}

@Test
void givenStableListForFiveTimesTable_thenVerifyElementsAreExpected() {
List<Integer> fiveTimesTable = StableValue.list(11, index -> index * 5);

assertThat(fiveTimesTable.get(0)).isEqualTo(0);
assertThat(fiveTimesTable.get(1)).isEqualTo(5);
assertThat(fiveTimesTable.get(2)).isEqualTo(10);
assertThat(fiveTimesTable.get(3)).isEqualTo(15);
assertThat(fiveTimesTable.get(4)).isEqualTo(20);
assertThat(fiveTimesTable.get(5)).isEqualTo(25);
assertThat(fiveTimesTable.get(6)).isEqualTo(30);
assertThat(fiveTimesTable.get(7)).isEqualTo(35);
assertThat(fiveTimesTable.get(8)).isEqualTo(40);
assertThat(fiveTimesTable.get(9)).isEqualTo(45);
assertThat(fiveTimesTable.get(10)).isEqualTo(50);
}

@Test
void givenStableMapForCityToCountry_thenVerifyValuesAreExpected() {
Map<String, String> cityToCountry = StableValue.map(cities, city -> expensiveMethodToDetermineCountry(city));

assertThat(cityToCountry.get("London")).isEqualTo("England");
assertThat(cityToCountry.get("Madrid")).isEqualTo("Spain");
assertThat(cityToCountry.get("Paris")).isEqualTo("France");
}

@BeforeEach
void init() {
cities = Set.of("London", "Madrid", "Paris");
}
}