diff --git a/common/src/main/java/org/apache/nemo/common/ir/vertex/transform/LatencymarkEmitTransform.java b/common/src/main/java/org/apache/nemo/common/ir/vertex/transform/LatencymarkEmitTransform.java
index eaa60b2..5ae9695 100644
--- a/common/src/main/java/org/apache/nemo/common/ir/vertex/transform/LatencymarkEmitTransform.java
+++ b/common/src/main/java/org/apache/nemo/common/ir/vertex/transform/LatencymarkEmitTransform.java
@@ -41,6 +41,7 @@
 
   /**
    * get OutputCollector.
+   * @return the output collector.
    */
   public OutputCollector<O> getOutputCollector() {
     return outputCollector;
diff --git a/common/src/main/java/org/apache/nemo/common/ir/vertex/transform/StreamTransform.java b/common/src/main/java/org/apache/nemo/common/ir/vertex/transform/StreamTransform.java
index e812a9d..97e7c09 100644
--- a/common/src/main/java/org/apache/nemo/common/ir/vertex/transform/StreamTransform.java
+++ b/common/src/main/java/org/apache/nemo/common/ir/vertex/transform/StreamTransform.java
@@ -24,7 +24,7 @@
 
 /**
  * A {@link Transform} relays input data from upstream vertex to downstream vertex promptly.
- * This transform can be used for merging input data into the {@link OutputCollector}.
+ * This transform can be used for merging input data into the {@link org.apache.nemo.common.ir.OutputCollector}.
  *
  * @param <T> input/output type.
  */