[samples/java]: Explain where tensor names came from.

Fixes https://github.com/tensorflow/tensorflow/issues/19348

samples/languages/java/training/src/main/java/Train.java

@@ -42,7 +42,10 @@ public class Train {
             Tensors.create(Paths.get(checkpointDir, "ckpt").toString())) {
       graph.importGraphDef(graphDef);
 
-      // Initialize or restore
+      // Initialize or restore.
+      // The names of the tensors in the graph are printed out by the program
+      // that created the graph:
+      // https://github.com/tensorflow/models/blob/master/samples/languages/java/training/model/create_graph.py
       if (checkpointExists) {
         sess.runner().feed("save/Const", checkpointPrefix).addTarget("save/restore_all").run();
       } else {
@@ -60,6 +63,8 @@ public class Train {
           float in = r.nextFloat();
           try (Tensor<Float> input = Tensors.create(in);
               Tensor<Float> target = Tensors.create(3 * in + 2)) {
+            // Again the tensor names are from the program that created the graph.
+            // https://github.com/tensorflow/models/blob/master/samples/languages/java/training/model/create_graph.py
             sess.runner().feed("input", input).feed("target", target).addTarget("train").run();
           }
         }
@@ -67,7 +72,9 @@ public class Train {
         printVariables(sess);
       }
 
-      // Checkpoint
+      // Checkpoint.
+      // The feed and target name are from the program that created the graph.
+      // https://github.com/tensorflow/models/blob/master/samples/languages/java/training/model/create_graph.py.
       sess.runner().feed("save/Const", checkpointPrefix).addTarget("save/control_dependency").run();
 
       // Example of "inference" in the same graph: