Java – How to enable the preview language features?

This article shows you how to use --enable-preview to enable the preview language features in Java 12, 13 and above.

P.S All preview features are disabled by default.

On JDK 12:

# compile
javac Example.java                                // Do not enable any preview features
javac --release 12 --enable-preview Example.java  // Enable all preview features of JDK 12
javac --release 11 --enable-preview Example.java  // DISALLOWED

#Run
java --enable-preview Example					  // Run with preview features of JDK 12

On JDK 13:

javac Example.java                                // Do not enable any preview features
javac --release 13 --enable-preview Example.java  // Enable all preview features of JDK 13
javac --release 12 --enable-preview Example.java  // DISALLOWED

java --enable-preview Example					  // Run with preview features of JDK 13

1. Maven

Enable preview features in Maven.

 <build>
	<plugins>
		<plugin>
			<groupId>org.apache.maven.plugins</groupId>
			<artifactId>maven-compiler-plugin</artifactId>
			<version>3.8.0</version>
			<configuration>
				<!-- 1.10, 11, 12, 13-->
				<release>13</release>
				<compilerArgs>
					--enable-preview
				</compilerArgs>
			</configuration>
		</plugin>
		<plugin>
			<groupId>org.apache.maven.plugins</groupId>
			<artifactId>maven-surefire-plugin</artifactId>
			<version>3.0.0-M3</version>
			<configuration>
				<argLine>--enable-preview</argLine>
			</configuration>
		</plugin>
	</plugins>
 </build>

2. Gradle

For Java 12, enable preview features in Gradle.

	tasks.withType(JavaCompile).each {
		it.options.compilerArgs.add('--enable-preview')
	}

	test {
		jvmArgs(['--enable-preview'])
	}

References

• JEP 12: Preview Language and VM Features
• Maven error: release version 1.13 not supported
• Java 13 – Switch Expressions
• Gradle is not working with Java 13