// functional/ProduceFunction.java
// (c)2021 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
import java.util.function.*;

interface
FuncSS extends Function<String, String> {}   // [1]

public class ProduceFunction {
  static FuncSS produce() {
    return s -> s.toLowerCase();             // [2]
  }
  public static void main(String[] args) {
    FuncSS f = produce();
    System.out.println(f.apply("YELLING"));
  }
}
/* Output:
yelling
*/