follow-up to #995 All SpanSubscription now fake QueueSubscription (#1008)

* follow-up to #995 All SpanSubscription now fake QueueSubscription

* Abide by checkstyle's rules

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/instrument/reactor/SpanSubscriber.java

@@ -16,19 +16,18 @@
 
 package org.springframework.cloud.sleuth.instrument.reactor;
 
-import java.util.concurrent.atomic.AtomicBoolean;
-
 import brave.Span;
 import brave.Tracer;
 import brave.Tracing;
 import brave.propagation.TraceContextOrSamplingFlags;
 import org.reactivestreams.Subscriber;
 import org.reactivestreams.Subscription;
-import reactor.core.Fuseable;
 import reactor.util.Logger;
 import reactor.util.Loggers;
 import reactor.util.context.Context;
 
+import java.util.concurrent.atomic.AtomicBoolean;
+
 /**
  * A trace representation of the {@link Subscriber}
  *
@@ -36,32 +35,7 @@ import reactor.util.context.Context;
  * @author Marcin Grzejszczak
  * @since 2.0.0
  */
-final class SpanSubscriber<T> extends AtomicBoolean implements SpanSubscription<T>, Fuseable.QueueSubscription<T> {
-
-	@Override
-	public T poll() {
-		return null;
-	}
-
-	@Override
-	public int requestFusion(int i) {
-		return Fuseable.NONE; //always negotiate to no fusion
-	}
-
-	@Override
-	public int size() {
-		return 0;
-	}
-
-	@Override
-	public boolean isEmpty() {
-		return true;
-	}
-
-	@Override
-	public void clear() {
-		//NO-OP
-	}
+final class SpanSubscriber<T> extends AtomicBoolean implements SpanSubscription<T> {
 
 	private static final Logger log = Loggers.getLogger(
 			SpanSubscriber.class);

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/instrument/reactor/SpanSubscription.java

@@ -18,9 +18,40 @@ package org.springframework.cloud.sleuth.instrument.reactor;
 
 import org.reactivestreams.Subscription;
 import reactor.core.CoreSubscriber;
+import reactor.core.Fuseable;
 
 /**
+ * A {@link SpanSubscription} is a {@link Subscription} that fakes being {@link Fuseable}
+ * (implementing {@link reactor.core.Fuseable.QueueSubscription} with default no-op methods
+ * and always negotiating fusion to be {@link Fuseable#NONE}).
+ *
  * @author Marcin Grzejszczak
  */
-interface SpanSubscription<T> extends Subscription, CoreSubscriber<T> {
+interface SpanSubscription<T> extends Subscription, CoreSubscriber<T>, Fuseable.QueueSubscription<T> {
+
+	@Override
+	default T poll() {
+		return null;
+	}
+
+	@Override
+	default int requestFusion(int i) {
+		return Fuseable.NONE; //always negotiate to no fusion
+	}
+
+	@Override
+	default int size() {
+		return 0;
+	}
+
+	@Override
+	default boolean isEmpty() {
+		return true;
+	}
+
+	@Override
+	default void clear() {
+		//NO-OP
+	}
+
 }