Why is Java Ignoring My serialVersionUID?

I've got a class which defines public static final Long serialVersionUID = 123L;.

When I actually serialize it or even if I run it through Java's serialver.exe it comes back with an arbitrary auto-generated serialVersionUID dependent on the method signatures at compilation time or however Java normally derives those.

Why is Java ignoring my explicitly specified serialVersionUID and how can I get it to stop?

Edit: Here's a minimal example which also demonstrates the above behavior.

pom.xml:

<?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>
    <groupId>demonstration</groupId>
    <artifactId>serialization</artifactId>
    <version>1.0</version>
    <packaging>jar</packaging>
    <properties>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>
</project>

src/main/java/demonstration/serialization/Example.java:

package demonstration.serialization;

import java.io.Serializable;

public class Example implements Serializable {
        private static final Long serialVersionUID = 123L;
}

Do an mvn clean package to create the output jar, then run the following command (modified as appropriate for your JDK):

"C:\Program Files\AdoptOpenJDK\jdk-14.0.1.7-openj9\bin\serialver.exe" -classpath target/serialization-1.0.jar demonstration.serialization.Example

I get back:

demonstration.serialization.Example:    private static final long serialVersionUID = 8528929994176475972L;

That's not the value of 123 that I specified. And in my slightly more complex example, the ObjectOuputStreams and ObjectInputStreams confirm that my specified values are being ignored.

Found the problem. Long is not the same as long; be sure when specifying a serialVersionUID that it matches the exact form:

private static final long serialVersionUID = [value]L;