dimitarp / java-8-11

Java Compiler Demo

Demo showing, that the Java compiler cannot detect usage of Java APIs, which are not available on previous Java versions. Instead runtime errors occur, if the execution path leads to a class/method not available in the JRE.

Project Structure

The project consists of two modules:

• lib: a library, which uses an API available only since Java 11, compiled with JDK 11 but with source and target equal to 8.
• app: a module, which uses the lib, but is compiled and run with JDK 8.

Running the Project

$ JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64 mvn -pl lib clean install

$ JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64 mvn -pl app clean verify

The last maven build shows the following error during test run:

Java11ApiExampleTest.test:10 » NoSuchMethod java.util.Optional.isEmpty()Z