Implement 'toString' method for some Emitters

src/main/java/io/reactivex/internal/operators/flowable/FlowableCreate.java

@@ -233,6 +233,11 @@ public boolean isCancelled() {
         public FlowableEmitter<T> serialize() {
             return this;
         }
+
+        @Override
+        public String toString() {
+            return emitter.toString();
+        }
     }
 
     abstract static class BaseEmitter<T>
@@ -338,6 +343,11 @@ public final long requested() {
         public final FlowableEmitter<T> serialize() {
             return new SerializedEmitter<T>(this);
         }
+
+        @Override
+        public String toString() {
+            return String.format("%s{%s}", getClass().getSimpleName(), super.toString());
+        }
     }
 
     static final class MissingEmitter<T> extends BaseEmitter<T> {

src/main/java/io/reactivex/internal/operators/observable/ObservableCreate.java

@@ -126,6 +126,11 @@ public void dispose() {
         public boolean isDisposed() {
             return DisposableHelper.isDisposed(get());
         }
+
+        @Override
+        public String toString() {
+            return String.format("%s{%s}", getClass().getSimpleName(), super.toString());
+        }
     }
 
     /**
@@ -279,6 +284,11 @@ public boolean isDisposed() {
         public ObservableEmitter<T> serialize() {
             return this;
         }
+
+        @Override
+        public String toString() {
+            return emitter.toString();
+        }
     }
 
 }

src/main/java/io/reactivex/internal/operators/single/SingleCreate.java

@@ -123,5 +123,10 @@ public void dispose() {
         public boolean isDisposed() {
             return DisposableHelper.isDisposed(get());
         }
+
+        @Override
+        public String toString() {
+            return String.format("%s{%s}", getClass().getSimpleName(), super.toString());
+        }
     }
 }