StreamConcat.java

import java.util.stream.Stream;
import org.junit.Test;

import static java.util.function.Function.identity;

public class StreamConcat {
   @SafeVarargs
   public static <T> Stream<T> concatenate(Stream<? extends T>... streams) {
      return Stream.of(streams).reduce(Stream.empty(), Stream::concat).map(identity());
   }

   @Test
   public void learnAboutConcatenate() {

      Stream<CharSequence> res = concatenate(
            Stream.of("One"),
            Stream.of(new StringBuffer("Two")),
            Stream.of(new StringBuilder("Three"))
      );

      res.forEach(System.out::println);
   }
}