Java "lambda expressions not supported at this language level"

In IntelliJ IDEA:

In File MenuProject StructureProject, change Project Language Level to 8.0 - Lambdas, type annotations etc.

For Android 3.0+ Go FileProject StructureModuleapp and In Properties Tab set Source Compatibility and Target Compatibility to 1.8 (Java 8)

Screenshot:

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You should change source code Language Level also on the Source tab (Modules part).

Change Language Level