[jira] [Created] (FLINK-9392) Add @FunctionalInterface annotations to all core functional interfaces

[Shang Yuanchun (Jira)]

Stephan Ewen created FLINK-9392:
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             Summary: Add @FunctionalInterface annotations to all core functional interfaces
                 Key: FLINK-9392
                 URL: https://issues.apache.org/jira/browse/FLINK-9392
             Project: Flink
          Issue Type: Improvement
          Components: Core
            Reporter: Stephan Ewen
            Assignee: Stephan Ewen


The {{@FunctionalInterface}} annotation should be added to all SAM interfaces in order to prevent accidentally breaking them (as non SAMs).

We had a case of that before for the {{SinkFunction}} which was compatible through default methods, but incompatible for users that previously instantiated that interface through a lambda.



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