add Java API to Duration

akka-actor-tests/src/test/java/akka/util/JavaDuration.java

@@ -0,0 +1,16 @@
+package akka.util;
+
+import org.junit.Test;
+
+public class JavaDuration {
+
+  @Test void testCreation() {
+    final Duration fivesec = Duration.create(5, "seconds");
+    final Duration threemillis = Duration.parse("3 millis");
+    final Duration diff = fivesec.minus(threemillis);
+    assert diff.lt(fivesec);
+    assert Duration.Zero().lteq(Duration.Inf());
+    assert Duration.Inf().gt(Duration.Zero().neg());
+  }
+
+}