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13 changes: 13 additions & 0 deletions content/md/articles/language/interop.md
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Expand Up @@ -690,6 +690,19 @@ Syntax error (IllegalArgumentException) compiling . at (REPL:4:29).
More than one matching method found: submit
```

## Clojure Functions may act as Functional Interfaces

Clojure developers can [invoke Java methods taking Functional Interfaces by passing functions](https://clojure.org/reference/java_interop#functional_interfaces)
with matching arity.

Example:

``` clojure
(.list (io/as-file "/tmp") (fn [_ fname] (str/ends-with? fname ".csv")))

;; Note: Here we need a type hint to help the compiler distinguish between FilenameFilter and FileFilter
(.listFiles (io/file "/tmp") ^java.io.FilenameFilter (fn [_ fname] (str/ends-with? fname ".json")))
```

## gen-class and How to Implement Java Classes in Clojure

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