Can't use latest Java Version (JDK 21) in Intellij IDEA – Java

The Problem:

I’m using macOS and want to leverage Java 21 in IntelliJ IDEA, but despite changing the Java version for the project, module, and OS, I am unable to utilize the new features of Java 21, such as String Templates. Although I have ensured the project SDK, module SDK, and OS Java version are set to 21, I still face this issue. How can I enable the use of Java 21 in IntelliJ IDEA?

The Solutions:

Solution 1: Update IntelliJ IDEA to 2023.2.2 and Set Language Level to 21 (Preview)

To use Java 21 features in IntelliJ IDEA on macOS:

1. Update IntelliJ IDEA to version 2023.2.2:
   • On Mac: Click “IntelliJ IDEA” in the menu bar and select “Check for Updates”.
   • On Windows/Linux: Go to “File” > “Settings” > “Appearance & Behavior” > “System Settings” > “Updates”.
2. Change the Language Level to 21 (preview):
   • Go to “File” > “Project Structure” > “Project”.
   • Under “Project SDK”, select Java 21.
   • Under “Language Level”, select “21 (preview)”.
   • Click “Apply” and then “OK”.

After following these steps, you should be able to use Java 21 features in IntelliJ IDEA.

Solution 2: Update Module SDK

If you have already completed the necessary steps to change the Java version of your project/module in Intellij IDEA but are still unable to use new Java 21 features, try the following:

1. Right-click on the module in your project and select “Open Module Settings” from the context menu.
2. In the “Module Settings” dialog box, navigate to the “SDKs” tab.
3. Click the “Add” button and select the JDK 21 installation that you want to use for the module.
4. If you don’t have JDK 21 installed, you can download it from the Oracle website or use the “Download JDK” option in the “Add SDK” dialog box.
5. Once you have added JDK 21 to the list of available SDKs, select it as the “Project SDK” and “Module SDK”.
6. Click “Apply” and then “OK” to save your changes.

This should enable you to use Java 21 features in your project.

Solution 3: Configure the compiler settings

If you have a Maven project, you can configure the compiler settings to use Java 21 by adding the following code to your pom.xml file:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <configuration>
                <source>21</source>
                <target>21</target>
                <compilerArgs>--enable-preview</compilerArgs>
            </configuration>
        </plugin>
    </plugins>
</build>

This will instruct Maven to use Java 21 as the source and target version for compilation, and to enable preview features (which are required for String templates).

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