diff --git a/akka-stream-tests/src/test/java/akka/stream/javadsl/FlowGraphTest.java b/akka-stream-tests/src/test/java/akka/stream/javadsl/FlowGraphTest.java
new file mode 100644
index 0000000000..90a3a05991
--- /dev/null
+++ b/akka-stream-tests/src/test/java/akka/stream/javadsl/FlowGraphTest.java
@@ -0,0 +1,154 @@
+package akka.stream.javadsl;
+
+import akka.actor.ActorRef;
+import akka.japi.Pair;
+import akka.stream.StreamTest;
+import akka.stream.stage.*;
+import akka.stream.javadsl.japi.*;
+import akka.stream.testkit.AkkaSpec;
+import akka.testkit.JavaTestKit;
+
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.reactivestreams.Publisher;
+import scala.concurrent.Await;
+import scala.concurrent.Future;
+import scala.concurrent.duration.FiniteDuration;
+import scala.runtime.BoxedUnit;
+
+import java.util.*;
+import java.util.concurrent.TimeUnit;
+
+import static org.junit.Assert.assertEquals;
+
+public class FlowGraphTest extends StreamTest {
+  public FlowGraphTest() {
+    super(actorSystemResource);
+  }
+
+  @ClassRule
+  public static AkkaJUnitActorSystemResource actorSystemResource = new AkkaJUnitActorSystemResource("FlowGraphTest",
+    AkkaSpec.testConf());
+
+  public <T> Creator<Stage<T, T>> op() {
+    return new akka.stream.javadsl.japi.Creator<Stage<T, T>>() {
+      @Override
+      public PushPullStage<T, T> create() throws Exception {
+        return new PushPullStage<T, T>() {
+          @Override
+          public Directive onPush(T element, Context<T> ctx) {
+            return ctx.push(element);
+          }
+
+          @Override
+          public Directive onPull(Context<T> ctx) {
+            return ctx.pull();
+          }
+        };
+      }
+    };
+  }
+
+  @Test
+  public void mustBeAbleToUseMerge() throws Exception {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final Flow<String, String> f1 = Flow.of(String.class).section(OperationAttributes.name("f1"), new Function<Flow<String, String>, Flow<String, String>>() {
+      @Override
+      public Flow<String, String> apply(Flow<String, String> flow) {
+        return flow.transform(FlowGraphTest.this.<String>op());
+      }
+    });
+    final Flow<String, String> f2 = Flow.of(String.class).section(OperationAttributes.name("f2"), new Function<Flow<String, String>, Flow<String, String>>() {
+      @Override
+      public Flow<String, String> apply(Flow<String, String> flow) {
+        return flow.transform(FlowGraphTest.this.<String>op());
+      }
+    });
+    final Flow<String, String> f3 = Flow.of(String.class).section(OperationAttributes.name("f3"), new Function<Flow<String, String>, Flow<String, String>>() {
+      @Override
+      public Flow<String, String> apply(Flow<String, String> flow) {
+        return flow.transform(FlowGraphTest.this.<String>op());
+      }
+    });
+
+    final Source<String> in1 = Source.from(Arrays.asList("a", "b", "c"));
+    final Source<String> in2 = Source.from(Arrays.asList("d", "e", "f"));
+
+    final KeyedSink<String, Publisher<String>> publisher = Sink.publisher();
+
+    final Merge<String> merge = Merge.<String>create();
+    MaterializedMap m = FlowGraph.builder().addEdge(in1, f1, merge).addEdge(in2, f2, merge)
+      .addEdge(merge, f3, publisher).build().run(materializer);
+
+    // collecting
+    final Publisher<String> pub = m.get(publisher);
+    final Future<List<String>> all = Source.from(pub).grouped(100).runWith(Sink.<List<String>>head(), materializer);
+
+    final List<String> result = Await.result(all, probe.dilated(FiniteDuration.create(3, TimeUnit.SECONDS)));
+    assertEquals(new HashSet<Object>(Arrays.asList("a", "b", "c", "d", "e", "f")), new HashSet<String>(result));
+  }
+
+  @Test
+  public void mustBeAbleToUseZip() {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final Iterable<String> input1 = Arrays.asList("A", "B", "C");
+    final Iterable<Integer> input2 = Arrays.asList(1, 2, 3);
+
+    final Source<String> in1 = Source.from(input1);
+    final Source<Integer> in2 = Source.from(input2);
+    final Zip<String, Integer> zip = Zip.create();
+    final KeyedSink<Pair<String, Integer>, Future<BoxedUnit>> out = Sink
+      .foreach(new Procedure<Pair<String, Integer>>() {
+        @Override
+        public void apply(Pair<String, Integer> param) throws Exception {
+          probe.getRef().tell(param, ActorRef.noSender());
+        }
+      });
+
+    FlowGraph.builder().addEdge(in1, zip.left()).addEdge(in2, zip.right()).addEdge(zip.out(), out).run(materializer);
+
+    List<Object> output = Arrays.asList(probe.receiveN(3));
+    @SuppressWarnings("unchecked")
+    List<Pair<String, Integer>> expected = Arrays.asList(new Pair<String, Integer>("A", 1), new Pair<String, Integer>(
+      "B", 2), new Pair<String, Integer>("C", 3));
+    assertEquals(expected, output);
+  }
+
+  @Test
+  public void mustBeAbleToUseUnzip() {
+    final JavaTestKit probe1 = new JavaTestKit(system);
+    final JavaTestKit probe2 = new JavaTestKit(system);
+
+    @SuppressWarnings("unchecked")
+    final List<Pair<String, Integer>> input = Arrays.asList(new Pair<String, Integer>("A", 1),
+      new Pair<String, Integer>("B", 2), new Pair<String, Integer>("C", 3));
+
+    final Iterable<String> expected1 = Arrays.asList("A", "B", "C");
+    final Iterable<Integer> expected2 = Arrays.asList(1, 2, 3);
+
+    final Source<Pair<String, Integer>> in = Source.from(input);
+    final Unzip<String, Integer> unzip = Unzip.create();
+
+    final KeyedSink<String, Future<BoxedUnit>> out1 = Sink.foreach(new Procedure<String>() {
+      @Override
+      public void apply(String param) throws Exception {
+        probe1.getRef().tell(param, ActorRef.noSender());
+      }
+    });
+    final KeyedSink<Integer, Future<BoxedUnit>> out2 = Sink.foreach(new Procedure<Integer>() {
+      @Override
+      public void apply(Integer param) throws Exception {
+        probe2.getRef().tell(param, ActorRef.noSender());
+      }
+    });
+
+    FlowGraph.builder().addEdge(in, unzip.in()).addEdge(unzip.left(), out1).addEdge(unzip.right(), out2)
+      .run(materializer);
+
+    List<Object> output1 = Arrays.asList(probe1.receiveN(3));
+    List<Object> output2 = Arrays.asList(probe2.receiveN(3));
+    assertEquals(expected1, output1);
+    assertEquals(expected2, output2);
+  }
+
+}
diff --git a/akka-stream-tests/src/test/java/akka/stream/javadsl/FlowTest.java b/akka-stream-tests/src/test/java/akka/stream/javadsl/FlowTest.java
index 185410a07b..8d1dceb6fb 100644
--- a/akka-stream-tests/src/test/java/akka/stream/javadsl/FlowTest.java
+++ b/akka-stream-tests/src/test/java/akka/stream/javadsl/FlowTest.java
@@ -3,7 +3,6 @@ package akka.stream.javadsl;
 import akka.actor.ActorRef;
 import akka.dispatch.Foreach;
 import akka.dispatch.Futures;
-import akka.dispatch.OnSuccess;
 import akka.japi.Pair;
 import akka.stream.OverflowStrategy;
 import akka.stream.StreamTest;
@@ -14,15 +13,10 @@ import akka.testkit.JavaTestKit;
 
 import org.junit.ClassRule;
 import org.junit.Test;
-import org.reactivestreams.Publisher;
 import scala.concurrent.Await;
 import scala.concurrent.Future;
-import scala.concurrent.duration.Duration;
 import scala.concurrent.duration.FiniteDuration;
-import scala.runtime.BoxedUnit;
-import scala.util.Try;
 import java.util.*;
-import java.util.concurrent.Callable;
 import java.util.concurrent.TimeUnit;
 import static org.junit.Assert.assertEquals;
 
@@ -41,8 +35,9 @@ public class FlowTest extends StreamTest {
     final String[] lookup = { "a", "b", "c", "d", "e", "f" };
     final java.lang.Iterable<Integer> input = Arrays.asList(0, 1, 2, 3, 4, 5);
     final Source<Integer> ints = Source.from(input);
-
-    ints.drop(2).take(3).takeWithin(FiniteDuration.create(10, TimeUnit.SECONDS)).map(new Function<Integer, String>() {
+    final Flow<Integer, String> flow1 = Flow.of(Integer.class).drop(2).take(3
+    ).takeWithin(FiniteDuration.create(10, TimeUnit.SECONDS
+    )).map(new Function<Integer, String>() {
       public String apply(Integer elem) {
         return lookup[elem];
       }
@@ -50,20 +45,25 @@ public class FlowTest extends StreamTest {
       public boolean test(String elem) {
         return !elem.equals("c");
       }
-    }).grouped(2).mapConcat(new Function<java.util.List<String>, java.util.List<String>>() {
+    });
+    final Flow<String, String> flow2 = Flow.of(String.class).grouped(2
+    ).mapConcat(new Function<java.util.List<String>, java.util.List<String>>() {
       public java.util.List<String> apply(java.util.List<String> elem) {
         return elem;
       }
-    }).groupedWithin(100, FiniteDuration.create(50, TimeUnit.MILLISECONDS))
-        .mapConcat(new Function<java.util.List<String>, java.util.List<String>>() {
+    }).groupedWithin(100, FiniteDuration.create(50, TimeUnit.MILLISECONDS)
+    ).mapConcat(new Function<java.util.List<String>, java.util.List<String>>() {
           public java.util.List<String> apply(java.util.List<String> elem) {
             return elem;
           }
-        }).fold("", new Function2<String, String, String>() {
+        });
+
+    ints.via(flow1.via(flow2)).fold("", new Function2<String, String, String>() {
           public String apply(String acc, String elem) {
             return acc + elem;
           }
-        }, materializer).foreach(new Foreach<String>() { // Scala Future
+        }, materializer
+    ).foreach(new Foreach<String>() { // Scala Future
               public void each(String elem) {
                 probe.getRef().tell(elem, ActorRef.noSender());
               }
@@ -72,37 +72,12 @@ public class FlowTest extends StreamTest {
     probe.expectMsgEquals("de");
   }
 
-  @Test
-  public void mustBeAbleToUseVoidTypeInForeach() {
-    final JavaTestKit probe = new JavaTestKit(system);
-    final java.lang.Iterable<String> input = Arrays.asList("a", "b", "c");
-    Source<String> ints = Source.from(input);
-
-    Future<BoxedUnit> completion = ints.foreach(new Procedure<String>() {
-      public void apply(String elem) {
-        probe.getRef().tell(elem, ActorRef.noSender());
-      }
-    }, materializer);
-
-    completion.onSuccess(new OnSuccess<BoxedUnit>() {
-      @Override
-      public void onSuccess(BoxedUnit elem) throws Throwable {
-        probe.getRef().tell(String.valueOf(elem), ActorRef.noSender());
-      }
-    }, system.dispatcher());
-
-    probe.expectMsgEquals("a");
-    probe.expectMsgEquals("b");
-    probe.expectMsgEquals("c");
-    probe.expectMsgEquals("()");
-  }
-
   @Test
   public void mustBeAbleToUseTransform() {
     final JavaTestKit probe = new JavaTestKit(system);
     final Iterable<Integer> input = Arrays.asList(0, 1, 2, 3, 4, 5, 6, 7);
     // duplicate each element, stop after 4 elements, and emit sum to the end
-    Source.from(input).transform(new Creator<Stage<Integer, Integer>>() {
+    final Flow<Integer, Integer> flow = Flow.of(Integer.class).transform(new Creator<Stage<Integer, Integer>>() {
       @Override
       public PushPullStage<Integer, Integer> create() throws Exception {
         return new StatefulStage<Integer, Integer>() {
@@ -133,7 +108,8 @@ public class FlowTest extends StreamTest {
           
         };
       }
-    }).foreach(new Procedure<Integer>() {
+    });
+    Source.from(input).via(flow).foreach(new Procedure<Integer>() {
       public void apply(Integer elem) {
         probe.getRef().tell(elem, ActorRef.noSender());
       }
@@ -154,11 +130,12 @@ public class FlowTest extends StreamTest {
   public void mustBeAbleToUseGroupBy() {
     final JavaTestKit probe = new JavaTestKit(system);
     final Iterable<String> input = Arrays.asList("Aaa", "Abb", "Bcc", "Cdd", "Cee");
-    Source.from(input).groupBy(new Function<String, String>() {
+    final Flow<String, Pair<String, Source<String>>> slsFlow= Flow.of(String.class).groupBy(new Function<String, String>() {
       public String apply(String elem) {
         return elem.substring(0, 1);
       }
-    }).foreach(new Procedure<Pair<String, Source<String>>>() {
+    });
+    Source.from(input).via(slsFlow).foreach(new Procedure<Pair<String, Source<String>>>() {
       @Override
       public void apply(final Pair<String, Source<String>> pair) throws Exception {
         pair.second().foreach(new Procedure<String>() {
@@ -190,11 +167,12 @@ public class FlowTest extends StreamTest {
   public void mustBeAbleToUseSplitWhen() {
     final JavaTestKit probe = new JavaTestKit(system);
     final Iterable<String> input = Arrays.asList("A", "B", "C", ".", "D", ".", "E", "F");
-    Source.from(input).splitWhen(new Predicate<String>() {
+    final Flow<String, Source<String>> flow = Flow.of(String.class).splitWhen(new Predicate<String>() {
       public boolean test(String elem) {
         return elem.equals(".");
       }
-    }).foreach(new Procedure<Source<String>>() {
+    });
+    Source.from(input).via(flow).foreach(new Procedure<Source<String>>() {
       @Override
       public void apply(Source<String> subStream) throws Exception {
         subStream.filter(new Predicate<String>() {
@@ -227,127 +205,6 @@ public class FlowTest extends StreamTest {
 
   }
 
-  public <T> Creator<Stage<T, T>> op() {
-    return new akka.stream.javadsl.japi.Creator<Stage<T, T>>() {
-      @Override
-      public PushPullStage<T, T> create() throws Exception {
-        return new PushPullStage<T, T>() {  
-          @Override
-          public Directive onPush(T element, Context<T> ctx) {
-            return ctx.push(element);
-          }
-          
-          @Override
-          public Directive onPull(Context<T> ctx) {
-            return ctx.pull();
-          }
-        };
-      }
-    };
-  }
-
-  @Test
-  public void mustBeAbleToUseMerge() throws Exception {
-    final Flow<String, String> f1 = Flow.of(String.class).section(OperationAttributes.name("f1"), new Function<Flow<String, String>, Flow<String, String>>() {
-      @Override
-      public Flow<String, String> apply(Flow<String, String> flow) {
-        return flow.transform(FlowTest.this.<String>op());
-      }
-    });
-    final Flow<String, String> f2 = Flow.of(String.class).section(OperationAttributes.name("f2"), new Function<Flow<String, String>, Flow<String, String>>() {
-      @Override
-      public Flow<String, String> apply(Flow<String, String> flow) {
-        return flow.transform(FlowTest.this.<String>op());
-      }
-    });
-    final Flow<String, String> f3 = Flow.of(String.class).section(OperationAttributes.name("f3"), new Function<Flow<String, String>, Flow<String, String>>() {
-      @Override
-      public Flow<String, String> apply(Flow<String, String> flow) {
-        return flow.transform(FlowTest.this.<String>op());
-      }
-    });
-
-    final Source<String> in1 = Source.from(Arrays.asList("a", "b", "c"));
-    final Source<String> in2 = Source.from(Arrays.asList("d", "e", "f"));
-
-    final KeyedSink<String, Publisher<String>> publisher = Sink.publisher();
-
-    // this is red in intellij, but actually valid, scalac generates bridge methods for Java, so inference *works*
-    final Merge<String> merge = Merge.<String> create();
-    MaterializedMap m = FlowGraph.builder().addEdge(in1, f1, merge).addEdge(in2, f2, merge)
-        .addEdge(merge, f3, publisher).build().run(materializer);
-
-    // collecting
-    final Publisher<String> pub = m.get(publisher);
-    final Future<List<String>> all = Source.from(pub).grouped(100).runWith(Sink.<List<String>>head(), materializer);
-
-    final List<String> result = Await.result(all, Duration.apply(200, TimeUnit.MILLISECONDS));
-    assertEquals(new HashSet<Object>(Arrays.asList("a", "b", "c", "d", "e", "f")), new HashSet<String>(result));
-  }
-
-  @Test
-  public void mustBeAbleToUseZip() {
-    final JavaTestKit probe = new JavaTestKit(system);
-    final Iterable<String> input1 = Arrays.asList("A", "B", "C");
-    final Iterable<Integer> input2 = Arrays.asList(1, 2, 3);
-
-    final Source<String> in1 = Source.from(input1);
-    final Source<Integer> in2 = Source.from(input2);
-    final Zip<String, Integer> zip = Zip.create();
-    final KeyedSink<Pair<String, Integer>, Future<BoxedUnit>> out = Sink
-        .foreach(new Procedure<Pair<String, Integer>>() {
-          @Override
-          public void apply(Pair<String, Integer> param) throws Exception {
-            probe.getRef().tell(param, ActorRef.noSender());
-          }
-        });
-
-    FlowGraph.builder().addEdge(in1, zip.left()).addEdge(in2, zip.right()).addEdge(zip.out(), out).run(materializer);
-
-    List<Object> output = Arrays.asList(probe.receiveN(3));
-    @SuppressWarnings("unchecked")
-    List<Pair<String, Integer>> expected = Arrays.asList(new Pair<String, Integer>("A", 1), new Pair<String, Integer>(
-        "B", 2), new Pair<String, Integer>("C", 3));
-    assertEquals(expected, output);
-  }
-
-  @Test
-  public void mustBeAbleToUseUnzip() {
-    final JavaTestKit probe1 = new JavaTestKit(system);
-    final JavaTestKit probe2 = new JavaTestKit(system);
-
-    @SuppressWarnings("unchecked")
-    final List<Pair<String, Integer>> input = Arrays.asList(new Pair<String, Integer>("A", 1),
-        new Pair<String, Integer>("B", 2), new Pair<String, Integer>("C", 3));
-
-    final Iterable<String> expected1 = Arrays.asList("A", "B", "C");
-    final Iterable<Integer> expected2 = Arrays.asList(1, 2, 3);
-
-    final Source<Pair<String, Integer>> in = Source.from(input);
-    final Unzip<String, Integer> unzip = Unzip.create();
-
-    final KeyedSink<String, Future<BoxedUnit>> out1 = Sink.foreach(new Procedure<String>() {
-      @Override
-      public void apply(String param) throws Exception {
-        probe1.getRef().tell(param, ActorRef.noSender());
-      }
-    });
-    final KeyedSink<Integer, Future<BoxedUnit>> out2 = Sink.foreach(new Procedure<Integer>() {
-      @Override
-      public void apply(Integer param) throws Exception {
-        probe2.getRef().tell(param, ActorRef.noSender());
-      }
-    });
-
-    FlowGraph.builder().addEdge(in, unzip.in()).addEdge(unzip.left(), out1).addEdge(unzip.right(), out2)
-        .run(materializer);
-
-    List<Object> output1 = Arrays.asList(probe1.receiveN(3));
-    List<Object> output2 = Arrays.asList(probe2.receiveN(3));
-    assertEquals(expected1, output1);
-    assertEquals(expected2, output2);
-  }
-
   @Test
   public void mustBeAbleToUseConcat() {
     final JavaTestKit probe = new JavaTestKit(system);
@@ -356,8 +213,8 @@ public class FlowTest extends StreamTest {
 
     final Source<String> in1 = Source.from(input1);
     final Source<String> in2 = Source.from(input2);
-
-    in1.concat(in2).foreach(new Procedure<String>() {
+    final Flow<String, String> flow = Flow.of(String.class);
+    in1.via(flow.concat(in2)).foreach(new Procedure<String>() {
       public void apply(String elem) {
         probe.getRef().tell(elem, ActorRef.noSender());
       }
@@ -367,80 +224,13 @@ public class FlowTest extends StreamTest {
     assertEquals(Arrays.asList("A", "B", "C", "D", "E", "F"), output);
   }
 
-  @Test
-  public void mustBeAbleToUseCallableInput() {
-    final JavaTestKit probe = new JavaTestKit(system);
-    final Iterable<Integer> input1 = Arrays.asList(4,3,2,1,0);
-    final akka.stream.javadsl.japi.Creator<Iterator<Integer>> input = new akka.stream.javadsl.japi.Creator<Iterator<Integer>>() {
-      @Override
-      public Iterator<Integer> create() {
-        return input1.iterator();
-      }
-    };
-    Source.from(input).foreach(new Procedure<Integer>() {
-      public void apply(Integer elem) {
-        probe.getRef().tell(elem, ActorRef.noSender());
-      }
-    }, materializer);
-
-    List<Object> output = Arrays.asList(probe.receiveN(5));
-    assertEquals(Arrays.asList(4, 3, 2, 1, 0), output);
-    probe.expectNoMsg(FiniteDuration.create(500, TimeUnit.MILLISECONDS));
-  }
-
-  @Test
-  public void mustBeAbleToUseOnCompleteSuccess() {
-    final JavaTestKit probe = new JavaTestKit(system);
-    final Iterable<String> input = Arrays.asList("A", "B", "C");
-
-    Source.from(input).runWith(Sink.<String> onComplete(new Procedure<BoxedUnit>() {
-      @Override
-      public void apply(BoxedUnit param) throws Exception {
-        probe.getRef().tell(param, ActorRef.noSender());
-      }
-    }), materializer);
-
-    probe.expectMsgClass(BoxedUnit.class);
-  }
-
-  @Test
-  public void mustBeAbleToUseOnCompleteError() {
-    final JavaTestKit probe = new JavaTestKit(system);
-    final Iterable<String> input = Arrays.asList("A", "B", "C");
-
-    Source.from(input).map(new Function<String, String>() {
-      public String apply(String arg0) throws Exception {
-        throw new RuntimeException("simulated err");
-      }
-    }).runWith(Sink.<String>head(), materializer).onComplete(new OnSuccess<Try<String>>() {
-      @Override
-      public void onSuccess(Try<String> e) throws Throwable {
-        if (e == null) {
-          probe.getRef().tell("done", ActorRef.noSender());
-        } else {
-          probe.getRef().tell(e.failed().get().getMessage(), ActorRef.noSender());
-        }
-      }
-    }, system.dispatcher());
-
-    probe.expectMsgEquals("simulated err");
-  }
-
-  @Test
-  public void mustBeAbleToUseToFuture() throws Exception {
-    final JavaTestKit probe = new JavaTestKit(system);
-    final Iterable<String> input = Arrays.asList("A", "B", "C");
-    Future<String> future = Source.from(input).runWith(Sink.<String>head(), materializer);
-    String result = Await.result(future, probe.dilated(FiniteDuration.create(3, TimeUnit.SECONDS)));
-    assertEquals("A", result);
-  }
-
   @Test
   public void mustBeAbleToUsePrefixAndTail() throws Exception {
     final JavaTestKit probe = new JavaTestKit(system);
     final Iterable<Integer> input = Arrays.asList(1, 2, 3, 4, 5, 6);
-    Future<Pair<List<Integer>, Source<Integer>>> future = Source.from(input).prefixAndTail(3)
-        .runWith(Sink.<Pair<List<Integer>, Source<Integer>>>head(), materializer);
+    final Flow<Integer, Pair<List<Integer>, Source<Integer>>> flow = Flow.of(Integer.class).prefixAndTail(3);
+    Future<Pair<List<Integer>, Source<Integer>>> future =
+            flow.runWith(Source.from(input), Sink.<Pair<List<Integer>, Source<Integer>>>head(), materializer);
     Pair<List<Integer>, Source<Integer>> result = Await.result(future,
         probe.dilated(FiniteDuration.create(3, TimeUnit.SECONDS)));
     assertEquals(Arrays.asList(1, 2, 3), result.first());
@@ -458,8 +248,9 @@ public class FlowTest extends StreamTest {
 
     final List<Source<Integer>> mainInputs = Arrays.asList(Source.from(input1), Source.from(input2));
 
-    Future<List<Integer>> future = Source.from(mainInputs)
-        .flatten(akka.stream.javadsl.FlattenStrategy.<Integer> concat()).grouped(6)
+    final Flow<Source<Integer>, List<Integer>> flow = Flow.<Source<Integer>>create().
+      flatten(akka.stream.javadsl.FlattenStrategy.<Integer> concat()).grouped(6);
+    Future<List<Integer>> future = Source.from(mainInputs).via(flow)
         .runWith(Sink.<List<Integer>>head(), materializer);
 
     List<Integer> result = Await.result(future, probe.dilated(FiniteDuration.create(3, TimeUnit.SECONDS)));
@@ -471,7 +262,8 @@ public class FlowTest extends StreamTest {
   public void mustBeAbleToUseBuffer() throws Exception {
     final JavaTestKit probe = new JavaTestKit(system);
     final List<String> input = Arrays.asList("A", "B", "C");
-    Future<List<String>> future = Source.from(input).buffer(2, OverflowStrategy.backpressure()).grouped(4)
+    final Flow<String, List<String>> flow = Flow.of(String.class).buffer(2, OverflowStrategy.backpressure()).grouped(4);
+    Future<List<String>> future = Source.from(input).via(flow)
         .runWith(Sink.<List<String>>head(), materializer);
 
     List<String> result = Await.result(future, probe.dilated(FiniteDuration.create(3, TimeUnit.SECONDS)));
@@ -481,33 +273,33 @@ public class FlowTest extends StreamTest {
   @Test
   public void mustBeAbleToUseConflate() throws Exception {
     final JavaTestKit probe = new JavaTestKit(system);
-    //    final List<String> input = Arrays.asList("A", "B", "C"); // test was fleaky // TODO FIXME, test was fleaky!
-    final List<String> input = Arrays.asList("C");
-    Future<String> future = Source.from(input).conflate(new Function<String, String>() {
+    final List<String> input = Arrays.asList("A", "B", "C");
+    final Flow<String, String> flow = Flow.of(String.class).conflate(new Function<String, String>() {
       @Override
       public String apply(String s) throws Exception {
         return s;
       }
     }, new Function2<String, String, String>() {
       @Override
-      public String apply(String in, String aggr) throws Exception {
-        return in;
+      public String apply(String aggr, String in) throws Exception {
+        return aggr + in;
       }
-    }).fold("", new Function2<String, String, String>() {
+    });
+    Future <String> future = Source.from(input).via(flow).fold("", new Function2<String, String, String>() {
       @Override
       public String apply(String aggr, String in) throws Exception {
-        return in;
+        return aggr + in;
       }
     }, materializer);
     String result = Await.result(future, probe.dilated(FiniteDuration.create(3, TimeUnit.SECONDS)));
-    assertEquals("C", result);
+    assertEquals("ABC", result);
   }
 
   @Test
   public void mustBeAbleToUseExpand() throws Exception {
     final JavaTestKit probe = new JavaTestKit(system);
     final List<String> input = Arrays.asList("A", "B", "C");
-    Future<String> future = Source.from(input).expand(new Function<String, String>() {
+    final Flow<String, String> flow = Flow.of(String.class).expand(new Function<String, String>() {
       @Override
       public String apply(String in) throws Exception {
         return in;
@@ -517,45 +309,24 @@ public class FlowTest extends StreamTest {
       public Pair<String, String> apply(String in) throws Exception {
         return new Pair<String, String>(in, in);
       }
-    }).runWith(Sink.<String>head(), materializer);
+    });
+    final KeyedSink<String, Future<String>> sink = Sink.<String>head();
+    MaterializedMap map = Source.from(input).to(flow.to(sink)).run(materializer);
+    Future<String> future = map.get(sink);
     String result = Await.result(future, probe.dilated(FiniteDuration.create(3, TimeUnit.SECONDS)));
     assertEquals("A", result);
   }
 
   @Test
-  public void mustProduceTicks() throws Exception {
-    final JavaTestKit probe = new JavaTestKit(system);
-    final Callable<String> tick = new Callable<String>() {
-      private int count = 1;
-
-      @Override
-      public String call() {
-        return "tick-" + (count++);
-      }
-    };
-    Source.from(FiniteDuration.create(1, TimeUnit.SECONDS), FiniteDuration.create(500, TimeUnit.MILLISECONDS), tick)
-        .foreach(new Procedure<String>() {
-          public void apply(String elem) {
-            probe.getRef().tell(elem, ActorRef.noSender());
-          }
-        }, materializer);
-    probe.expectNoMsg(FiniteDuration.create(600, TimeUnit.MILLISECONDS));
-    probe.expectMsgEquals("tick-1");
-    probe.expectNoMsg(FiniteDuration.create(200, TimeUnit.MILLISECONDS));
-    probe.expectMsgEquals("tick-2");
-    probe.expectNoMsg(FiniteDuration.create(200, TimeUnit.MILLISECONDS));
-
-  }
-
-  @Test
-  public void mustBeAbleToUseMapFuture() throws Exception {
+  public void mustBeAbleToUseMapAsync() throws Exception {
     final JavaTestKit probe = new JavaTestKit(system);
     final Iterable<String> input = Arrays.asList("a", "b", "c");
-    Source.from(input).mapAsync(new Function<String, Future<String>>() {
+    final Flow<String, String> flow = Flow.of(String.class).mapAsync(new Function<String, Future<String>>() {
       public Future<String> apply(String elem) {
         return Futures.successful(elem.toUpperCase());
       }
-    }).foreach(new Procedure<String>() {
+    });
+    Source.from(input).via(flow).foreach(new Procedure<String>() {
       public void apply(String elem) {
         probe.getRef().tell(elem, ActorRef.noSender());
       }
@@ -564,5 +335,4 @@ public class FlowTest extends StreamTest {
     probe.expectMsgEquals("B");
     probe.expectMsgEquals("C");
   }
-
 }
diff --git a/akka-stream-tests/src/test/java/akka/stream/javadsl/SourceTest.java b/akka-stream-tests/src/test/java/akka/stream/javadsl/SourceTest.java
new file mode 100644
index 0000000000..16149a8618
--- /dev/null
+++ b/akka-stream-tests/src/test/java/akka/stream/javadsl/SourceTest.java
@@ -0,0 +1,455 @@
+package akka.stream.javadsl;
+
+import akka.actor.ActorRef;
+import akka.dispatch.Foreach;
+import akka.dispatch.Futures;
+import akka.dispatch.OnSuccess;
+import akka.japi.Pair;
+import akka.stream.OverflowStrategy;
+import akka.stream.StreamTest;
+import akka.stream.stage.*;
+import akka.stream.javadsl.japi.*;
+import akka.stream.testkit.AkkaSpec;
+import akka.testkit.JavaTestKit;
+
+import org.junit.ClassRule;
+import org.junit.Test;
+import scala.concurrent.Await;
+import scala.concurrent.Future;
+import scala.concurrent.duration.FiniteDuration;
+import scala.runtime.BoxedUnit;
+import scala.util.Try;
+
+import java.util.*;
+import java.util.concurrent.Callable;
+import java.util.concurrent.TimeUnit;
+
+import static org.junit.Assert.assertEquals;
+
+public class SourceTest extends StreamTest {
+  public SourceTest() {
+    super(actorSystemResource);
+  }
+
+  @ClassRule
+  public static AkkaJUnitActorSystemResource actorSystemResource = new AkkaJUnitActorSystemResource("SourceTest",
+    AkkaSpec.testConf());
+
+  @Test
+  public void mustBeAbleToUseSimpleOperators() {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final String[] lookup = {"a", "b", "c", "d", "e", "f"};
+    final java.lang.Iterable<Integer> input = Arrays.asList(0, 1, 2, 3, 4, 5);
+    final Source<Integer> ints = Source.from(input);
+
+    ints.drop(2).take(3).takeWithin(FiniteDuration.create(10, TimeUnit.SECONDS)).map(new Function<Integer, String>() {
+      public String apply(Integer elem) {
+        return lookup[elem];
+      }
+    }).filter(new Predicate<String>() {
+      public boolean test(String elem) {
+        return !elem.equals("c");
+      }
+    }).grouped(2).mapConcat(new Function<java.util.List<String>, java.util.List<String>>() {
+      public java.util.List<String> apply(java.util.List<String> elem) {
+        return elem;
+      }
+    }).groupedWithin(100, FiniteDuration.create(50, TimeUnit.MILLISECONDS))
+      .mapConcat(new Function<java.util.List<String>, java.util.List<String>>() {
+        public java.util.List<String> apply(java.util.List<String> elem) {
+          return elem;
+        }
+      }).fold("", new Function2<String, String, String>() {
+      public String apply(String acc, String elem) {
+        return acc + elem;
+      }
+    }, materializer).foreach(new Foreach<String>() { // Scala Future
+      public void each(String elem) {
+        probe.getRef().tell(elem, ActorRef.noSender());
+      }
+    }, system.dispatcher());
+
+    probe.expectMsgEquals("de");
+  }
+
+  @Test
+  public void mustBeAbleToUseVoidTypeInForeach() {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final java.lang.Iterable<String> input = Arrays.asList("a", "b", "c");
+    Source<String> ints = Source.from(input);
+
+    Future<BoxedUnit> completion = ints.foreach(new Procedure<String>() {
+      public void apply(String elem) {
+        probe.getRef().tell(elem, ActorRef.noSender());
+      }
+    }, materializer);
+
+    completion.onSuccess(new OnSuccess<BoxedUnit>() {
+      @Override
+      public void onSuccess(BoxedUnit elem) throws Throwable {
+        probe.getRef().tell(String.valueOf(elem), ActorRef.noSender());
+      }
+    }, system.dispatcher());
+
+    probe.expectMsgEquals("a");
+    probe.expectMsgEquals("b");
+    probe.expectMsgEquals("c");
+    probe.expectMsgEquals("()");
+  }
+
+  @Test
+  public void mustBeAbleToUseTransform() {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final Iterable<Integer> input = Arrays.asList(0, 1, 2, 3, 4, 5, 6, 7);
+    // duplicate each element, stop after 4 elements, and emit sum to the end
+    Source.from(input).transform(new Creator<Stage<Integer, Integer>>() {
+      @Override
+      public PushPullStage<Integer, Integer> create() throws Exception {
+        return new StatefulStage<Integer, Integer>() {
+          int sum = 0;
+          int count = 0;
+
+          @Override
+          public StageState<Integer, Integer> initial() {
+            return new StageState<Integer, Integer>() {
+              @Override
+              public Directive onPush(Integer element, Context<Integer> ctx) {
+                sum += element;
+                count += 1;
+                if (count == 4) {
+                  return emitAndFinish(Arrays.asList(element, element, sum).iterator(), ctx);
+                } else {
+                  return emit(Arrays.asList(element, element).iterator(), ctx);
+                }
+              }
+
+            };
+          }
+
+          @Override
+          public TerminationDirective onUpstreamFinish(Context<Integer> ctx) {
+            return terminationEmit(Collections.singletonList(sum).iterator(), ctx);
+          }
+
+        };
+      }
+    }).foreach(new Procedure<Integer>() {
+      public void apply(Integer elem) {
+        probe.getRef().tell(elem, ActorRef.noSender());
+      }
+    }, materializer);
+
+    probe.expectMsgEquals(0);
+    probe.expectMsgEquals(0);
+    probe.expectMsgEquals(1);
+    probe.expectMsgEquals(1);
+    probe.expectMsgEquals(2);
+    probe.expectMsgEquals(2);
+    probe.expectMsgEquals(3);
+    probe.expectMsgEquals(3);
+    probe.expectMsgEquals(6);
+  }
+
+  @Test
+  public void mustBeAbleToUseGroupBy() {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final Iterable<String> input = Arrays.asList("Aaa", "Abb", "Bcc", "Cdd", "Cee");
+    Source.from(input).groupBy(new Function<String, String>() {
+      public String apply(String elem) {
+        return elem.substring(0, 1);
+      }
+    }).foreach(new Procedure<Pair<String, Source<String>>>() {
+      @Override
+      public void apply(final Pair<String, Source<String>> pair) throws Exception {
+        pair.second().foreach(new Procedure<String>() {
+          @Override
+          public void apply(String elem) throws Exception {
+            probe.getRef().tell(new Pair<String, String>(pair.first(), elem), ActorRef.noSender());
+          }
+        }, materializer);
+      }
+    }, materializer);
+
+    Map<String, List<String>> grouped = new HashMap<String, List<String>>();
+    for (Object o : probe.receiveN(5)) {
+      @SuppressWarnings("unchecked")
+      Pair<String, String> p = (Pair<String, String>) o;
+      List<String> g = grouped.get(p.first());
+      if (g == null) {
+        g = new ArrayList<String>();
+      }
+      g.add(p.second());
+      grouped.put(p.first(), g);
+    }
+
+    assertEquals(Arrays.asList("Aaa", "Abb"), grouped.get("A"));
+
+  }
+
+  @Test
+  public void mustBeAbleToUseSplitWhen() {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final Iterable<String> input = Arrays.asList("A", "B", "C", ".", "D", ".", "E", "F");
+    Source.from(input).splitWhen(new Predicate<String>() {
+      public boolean test(String elem) {
+        return elem.equals(".");
+      }
+    }).foreach(new Procedure<Source<String>>() {
+      @Override
+      public void apply(Source<String> subStream) throws Exception {
+        subStream.filter(new Predicate<String>() {
+          @Override
+          public boolean test(String elem) {
+            return !elem.equals(".");
+          }
+        }).grouped(10).foreach(new Procedure<List<String>>() {
+          @Override
+          public void apply(List<String> chunk) throws Exception {
+            probe.getRef().tell(chunk, ActorRef.noSender());
+          }
+        }, materializer);
+      }
+    }, materializer);
+
+    for (Object o : probe.receiveN(3)) {
+      @SuppressWarnings("unchecked")
+      List<String> chunk = (List<String>) o;
+      if (chunk.get(0).equals("A")) {
+        assertEquals(Arrays.asList("A", "B", "C"), chunk);
+      } else if (chunk.get(0).equals("D")) {
+        assertEquals(Arrays.asList("D"), chunk);
+      } else if (chunk.get(0).equals("E")) {
+        assertEquals(Arrays.asList("E", "F"), chunk);
+      } else {
+        assertEquals("[A, B, C] or [D] or [E, F]", chunk);
+      }
+    }
+
+  }
+
+  @Test
+  public void mustBeAbleToUseConcat() {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final Iterable<String> input1 = Arrays.asList("A", "B", "C");
+    final Iterable<String> input2 = Arrays.asList("D", "E", "F");
+
+    final Source<String> in1 = Source.from(input1);
+    final Source<String> in2 = Source.from(input2);
+
+    in1.concat(in2).foreach(new Procedure<String>() {
+      public void apply(String elem) {
+        probe.getRef().tell(elem, ActorRef.noSender());
+      }
+    }, materializer);
+
+    List<Object> output = Arrays.asList(probe.receiveN(6));
+    assertEquals(Arrays.asList("A", "B", "C", "D", "E", "F"), output);
+  }
+
+  @Test
+  public void mustBeAbleToUseCallableInput() {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final Iterable<Integer> input1 = Arrays.asList(4, 3, 2, 1, 0);
+    final akka.stream.javadsl.japi.Creator<Iterator<Integer>> input = new akka.stream.javadsl.japi.Creator<Iterator<Integer>>() {
+      @Override
+      public Iterator<Integer> create() {
+        return input1.iterator();
+      }
+    };
+    Source.from(input).foreach(new Procedure<Integer>() {
+      public void apply(Integer elem) {
+        probe.getRef().tell(elem, ActorRef.noSender());
+      }
+    }, materializer);
+
+    List<Object> output = Arrays.asList(probe.receiveN(5));
+    assertEquals(Arrays.asList(4, 3, 2, 1, 0), output);
+    probe.expectNoMsg(FiniteDuration.create(500, TimeUnit.MILLISECONDS));
+  }
+
+  @Test
+  public void mustBeAbleToUseOnCompleteSuccess() {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final Iterable<String> input = Arrays.asList("A", "B", "C");
+
+    Source.from(input).runWith(Sink.<String>onComplete(new Procedure<BoxedUnit>() {
+      @Override
+      public void apply(BoxedUnit param) throws Exception {
+        probe.getRef().tell(param, ActorRef.noSender());
+      }
+    }), materializer);
+
+    probe.expectMsgClass(BoxedUnit.class);
+  }
+
+  @Test
+  public void mustBeAbleToUseOnCompleteError() {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final Iterable<String> input = Arrays.asList("A", "B", "C");
+
+    Source.from(input).map(new Function<String, String>() {
+      public String apply(String arg0) throws Exception {
+        throw new RuntimeException("simulated err");
+      }
+    }).runWith(Sink.<String>head(), materializer).onComplete(new OnSuccess<Try<String>>() {
+      @Override
+      public void onSuccess(Try<String> e) throws Throwable {
+        if (e == null) {
+          probe.getRef().tell("done", ActorRef.noSender());
+        } else {
+          probe.getRef().tell(e.failed().get().getMessage(), ActorRef.noSender());
+        }
+      }
+    }, system.dispatcher());
+
+    probe.expectMsgEquals("simulated err");
+  }
+
+  @Test
+  public void mustBeAbleToUseToFuture() throws Exception {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final Iterable<String> input = Arrays.asList("A", "B", "C");
+    Future<String> future = Source.from(input).runWith(Sink.<String>head(), materializer);
+    String result = Await.result(future, probe.dilated(FiniteDuration.create(3, TimeUnit.SECONDS)));
+    assertEquals("A", result);
+  }
+
+  @Test
+  public void mustBeAbleToUsePrefixAndTail() throws Exception {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final Iterable<Integer> input = Arrays.asList(1, 2, 3, 4, 5, 6);
+    Future<Pair<List<Integer>, Source<Integer>>> future = Source.from(input).prefixAndTail(3)
+      .runWith(Sink.<Pair<List<Integer>, Source<Integer>>>head(), materializer);
+    Pair<List<Integer>, Source<Integer>> result = Await.result(future,
+      probe.dilated(FiniteDuration.create(3, TimeUnit.SECONDS)));
+    assertEquals(Arrays.asList(1, 2, 3), result.first());
+
+    Future<List<Integer>> tailFuture = result.second().grouped(4).runWith(Sink.<List<Integer>>head(), materializer);
+    List<Integer> tailResult = Await.result(tailFuture, probe.dilated(FiniteDuration.create(3, TimeUnit.SECONDS)));
+    assertEquals(Arrays.asList(4, 5, 6), tailResult);
+  }
+
+  @Test
+  public void mustBeAbleToUseConcatAllWithSources() throws Exception {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final Iterable<Integer> input1 = Arrays.asList(1, 2, 3);
+    final Iterable<Integer> input2 = Arrays.asList(4, 5);
+
+    final List<Source<Integer>> mainInputs = Arrays.asList(Source.from(input1), Source.from(input2));
+
+    Future<List<Integer>> future = Source.from(mainInputs)
+      .flatten(akka.stream.javadsl.FlattenStrategy.<Integer>concat()).grouped(6)
+      .runWith(Sink.<List<Integer>>head(), materializer);
+
+    List<Integer> result = Await.result(future, probe.dilated(FiniteDuration.create(3, TimeUnit.SECONDS)));
+
+    assertEquals(Arrays.asList(1, 2, 3, 4, 5), result);
+  }
+
+  @Test
+  public void mustBeAbleToUseBuffer() throws Exception {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final List<String> input = Arrays.asList("A", "B", "C");
+    Future<List<String>> future = Source.from(input).buffer(2, OverflowStrategy.backpressure()).grouped(4)
+      .runWith(Sink.<List<String>>head(), materializer);
+
+    List<String> result = Await.result(future, probe.dilated(FiniteDuration.create(3, TimeUnit.SECONDS)));
+    assertEquals(input, result);
+  }
+
+  @Test
+  public void mustBeAbleToUseConflate() throws Exception {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final List<String> input = Arrays.asList("A", "B", "C");
+    Future<String> future = Source.from(input).conflate(new Function<String, String>() {
+      @Override
+      public String apply(String s) throws Exception {
+        return s;
+      }
+    }, new Function2<String, String, String>() {
+      @Override
+      public String apply(String aggr, String in) throws Exception {
+        return aggr + in;
+      }
+    }).fold("", new Function2<String, String, String>() {
+      @Override
+      public String apply(String aggr, String in) throws Exception {
+        return aggr + in;
+      }
+    }, materializer);
+    String result = Await.result(future, probe.dilated(FiniteDuration.create(3, TimeUnit.SECONDS)));
+    assertEquals("ABC", result);
+  }
+
+  @Test
+  public void mustBeAbleToUseExpand() throws Exception {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final List<String> input = Arrays.asList("A", "B", "C");
+    Future<String> future = Source.from(input).expand(new Function<String, String>() {
+      @Override
+      public String apply(String in) throws Exception {
+        return in;
+      }
+    }, new Function<String, Pair<String, String>>() {
+      @Override
+      public Pair<String, String> apply(String in) throws Exception {
+        return new Pair<String, String>(in, in);
+      }
+    }).runWith(Sink.<String>head(), materializer);
+    String result = Await.result(future, probe.dilated(FiniteDuration.create(3, TimeUnit.SECONDS)));
+    assertEquals("A", result);
+  }
+
+  @Test
+  public void mustProduceTicks() throws Exception {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final Callable<String> tick = new Callable<String>() {
+      private int count = 1;
+
+      @Override
+      public String call() {
+        return "tick-" + (count++);
+      }
+    };
+    Source.from(FiniteDuration.create(1, TimeUnit.SECONDS), FiniteDuration.create(500, TimeUnit.MILLISECONDS), tick)
+      .foreach(new Procedure<String>() {
+        public void apply(String elem) {
+          probe.getRef().tell(elem, ActorRef.noSender());
+        }
+      }, materializer);
+    probe.expectNoMsg(FiniteDuration.create(600, TimeUnit.MILLISECONDS));
+    probe.expectMsgEquals("tick-1");
+    probe.expectNoMsg(FiniteDuration.create(200, TimeUnit.MILLISECONDS));
+    probe.expectMsgEquals("tick-2");
+    probe.expectNoMsg(FiniteDuration.create(200, TimeUnit.MILLISECONDS));
+
+  }
+
+  @Test
+  public void mustBeAbleToUseMapFuture() throws Exception {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final Iterable<String> input = Arrays.asList("a", "b", "c");
+    Source.from(input).mapAsync(new Function<String, Future<String>>() {
+      public Future<String> apply(String elem) {
+        return Futures.successful(elem.toUpperCase());
+      }
+    }).foreach(new Procedure<String>() {
+      public void apply(String elem) {
+        probe.getRef().tell(elem, ActorRef.noSender());
+      }
+    }, materializer);
+    probe.expectMsgEquals("A");
+    probe.expectMsgEquals("B");
+    probe.expectMsgEquals("C");
+  }
+
+  @Test
+  public void mustWorkFromFuture() throws Exception {
+    final JavaTestKit probe = new JavaTestKit(system);
+    final Iterable<String> input = Arrays.asList("A", "B", "C");
+    Future<String> future1 = Source.from(input).runWith(Sink.<String>head(), materializer);
+    Future<String> future2 = Source.from(future1).runWith(Sink.<String>head(), materializer);
+    String result = Await.result(future2, probe.dilated(FiniteDuration.create(3, TimeUnit.SECONDS)));
+    assertEquals("A", result);
+  }
+}
diff --git a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowFoldSpec.scala b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowFoldSpec.scala
index e400013866..f4699229a3 100644
--- a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowFoldSpec.scala
+++ b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowFoldSpec.scala
@@ -6,7 +6,7 @@ package akka.stream.scaladsl
 import scala.concurrent.Await
 import scala.util.control.NoStackTrace
 
-import akka.stream.FlowMaterializer
+import akka.stream.{ OverflowStrategy, FlowMaterializer }
 import akka.stream.testkit.AkkaSpec
 import akka.testkit.DefaultTimeout
 
diff --git a/akka-stream/src/main/scala/akka/stream/javadsl/Flow.scala b/akka-stream/src/main/scala/akka/stream/javadsl/Flow.scala
index e792cb2c2a..ed568c6d57 100644
--- a/akka-stream/src/main/scala/akka/stream/javadsl/Flow.scala
+++ b/akka-stream/src/main/scala/akka/stream/javadsl/Flow.scala
@@ -111,7 +111,7 @@ class Flow[-In, +Out](delegate: scaladsl.Flow[In, Out]) {
    * @tparam T materialized type of given KeyedSink
    */
   def runWith[T](source: javadsl.Source[In], sink: javadsl.KeyedSink[Out, T], materializer: FlowMaterializer): T =
-    delegate.runWith(source.asScala, sink.asScala)(materializer).asInstanceOf[T]
+    delegate.runWith(source.asScala, sink.asScala)(materializer)._2.asInstanceOf[T]
 
   /**
    * Connect the `KeyedSource` to this `Flow` and then connect it to the `Sink` and run it.
@@ -121,7 +121,7 @@ class Flow[-In, +Out](delegate: scaladsl.Flow[In, Out]) {
    * @tparam T materialized type of given KeyedSource
    */
   def runWith[T](source: javadsl.KeyedSource[In, T], sink: javadsl.Sink[Out], materializer: FlowMaterializer): T =
-    delegate.runWith(source.asScala, sink.asScala)(materializer).asInstanceOf[T]
+    delegate.runWith(source.asScala, sink.asScala)(materializer)._1.asInstanceOf[T]
 
   /**
    * Connect the `Source` to this `Flow` and then connect it to the `Sink` and run it.
diff --git a/akka-stream/src/main/scala/akka/stream/javadsl/Source.scala b/akka-stream/src/main/scala/akka/stream/javadsl/Source.scala
index 59c5530fa7..2db9a4bc16 100644
--- a/akka-stream/src/main/scala/akka/stream/javadsl/Source.scala
+++ b/akka-stream/src/main/scala/akka/stream/javadsl/Source.scala
@@ -208,7 +208,7 @@ class Source[+Out](delegate: scaladsl.Source[Out]) {
    * source.
    */
   def concat[Out2 >: Out](second: Source[Out2]): Source[Out2] =
-    delegate.concat(second.asScala).asJava
+    Source.concat(this, second)
 
   /**
    * Shortcut for running this `Source` with a foreach procedure. The given procedure is invoked