Error running project on idea “The diamond operator is not supported in – source 1.5”, because lambda expressions, a new feature in Java 8, have been used in the project. Of course, the syntax of 1.5 is not supported.

Solution:

1. Ensure that the bytecode compilation version in Java compiler in setting in idea is 8

2. Modify the language level of the module in the project structure to 8.

3. Check the pom.xml file of Maven project to see if the following attributes are added.

<properties>
    <maven.compiler.source>8</maven.compiler.source>
    <maven.compiler.target>8</maven.compiler.target>
</properties>