Most likely you have incorrect compiler options imported from Maven here:
Also check project and module bytecode (target) version settings outlined on the screenshot.
Other places where the source language level is configured:
- Project Structure | Project
- Project Structure | Modules (check every module) | Sources
Maven default language level is 1.5 (5.0), you will see this version as the Module language level on the screenshot above.
This can be changed using maven-compiler-plugin configuration inside pom.xml
:
<project>
[...]
<build>
[...]
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
[...]
</build>
[...]
</project>
or
<project>
[...]
<properties>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>
[...]
</project>
IntelliJ IDEA will respect this setting after you Reimport the Maven project in the Maven Projects tool window: