intellij idea java: diamond operator is not supported in -source 1.5

Just add the red part. My jdk is version 1.8, modify it according to the actual situation. 
<? xml version = "1.0" encoding = "UTF-8" ?> 
< project xmlns = "http://maven.apache.org/POM/4.0.0" xmlns: xsi = "http: //www.w3 .org / 2001 / XMLSchema-instance " xsi : schemaLocation =" http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd " > < modelVersion > 4.0.0 </ modelVersion > < groupId > org.example </ groupId > < artifactId > maven_java <
 
 




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>1.8</source>
 <target>1.8</target>
 </configuration>
 </plugin>
 </plugins>
 </build>

</project>