Java Language Changes for Java SE 9 https://docs.oracle.com/javase/9/language/toc.htm#JSLAN-GUID-16A5183A-DC0D-4A96-B9D8-AAC9671222DD
From Java 9, the _ character cannot be used as an identifier anymore, not just within the lambda context
The underscore character is not a legal name.
If you use the underscore character ("_") an identifier, your source code can no longer be compiled.
Angel Koh
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