CODEWITHSUNDEEP
javamaven
Berkin
Berkin

Reputation: 1664

Can't Compile Java 11 Code With Source Options

I am trying to test cross compilation between modules. I have a module which uses java 1.8 and another module uses Java 11. I am trying to use Java 11 module as dependency on Java 1.8 project. When I try to compile Java 11 module, maven shows an error.

MAIN MODULE

<project>
        <dependencies>
            <dependency>
                <groupId>com.berkin</groupId>
                <artifactId>java</artifactId>
                <version>1.0-SNAPSHOT</version>
            </dependency>
        </dependencies>

        <build>
            <plugins>
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-compiler-plugin</artifactId>
                    <version>3.8.1</version>
                    <configuration>
                        <source>1.8</source>
                        <target>1.8</target>
                    </configuration>
                </plugin>
            </plugins>
        </build>
</project>

SECONDARY MODULE NAMED JAVA

<project>
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.berkin</groupId>
    <artifactId>java</artifactId>
    <version>1.0-SNAPSHOT</version>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <source>11</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

CODE ON SECONDARY MODULE

public class Test {
    public void test(){
        System.out.println(" ".isEmpty()); //true
    }
}

In theory I should able to compile secondary module with java 11 compiler and use it in min Java 8 JRE. Thus I can also use it in Java 8 project as a dependency. Where am I missing?

ERROR

 Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.1:compile (default-compile) on project java: Fatal error compiling: invalid source release: 11 -> [Help 1]

Thanks.

Upvotes: 0

Views: 1204

Answers (2)

Berkin
Berkin

Reputation: 1664

I get it thanks to @Elliott Frisch

There are several terms;

Java Compiler : It is defined by JAVA_HOME or if you override by selecting another Java version for Maven thats it. You can compile Java 6 codes with Java 11 compiler. Because it has backward compatibility.

Source : Minimum Java version which you want to use java features. For example, if I want to use lambdas, at least I have to use source 8. If I want to use Java 11 features, I need to set it to 11. Its all about Java Features that you want to use

Target : Minimum JRE version which can run my features. E.g. if I set Java 8, I need at least JRE 8 to use lambdas. I can't use JRE 7 or lower because they don't know what lambda is.

Also

If java compiler version is 8, it can't compile source 11 classes. Because compiler don't know how to compile Java 11. I failed at the beginning because I had lower than source. When I changed into 11 & 11, I failed again because this time compiler was older(It was Java 8)

Thanks

Upvotes: 0

Robert Scholte
Robert Scholte

Reputation: 12335

The main reason is that you cannot use a source value that is lower than the target value. If you want the code to be compatible with Java 1.8, lower the source to 1.8

Upvotes: 1

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