Refactor Datastore example, add example on embedded entities (#980)

* Refactor Datastore example, add example on embedded entities

* Minor refactoring of examples
- Favor printf over println
- Rename Action argument from request to arg

gcloud-java-examples/README.md

@@ -81,6 +81,7 @@ To run examples from your command line:
     mvn exec:java -Dexec.mainClass="com.google.cloud.examples.datastore.DatastoreExample" -Dexec.args="your-project-id my_name add my\ comment"
     mvn exec:java -Dexec.mainClass="com.google.cloud.examples.datastore.DatastoreExample" -Dexec.args="your-project-id my_name display"
     mvn exec:java -Dexec.mainClass="com.google.cloud.examples.datastore.DatastoreExample" -Dexec.args="your-project-id my_name delete"
+    mvn exec:java -Dexec.mainClass="com.google.cloud.examples.datastore.DatastoreExample" -Dexec.args="your-project-id my_name set [email protected] 1234"
     ```
 
   * Here's an example run of `DnsExample`.

gcloud-java-examples/src/main/java/com/google/cloud/examples/bigquery/BigQueryExample.java

@@ -108,7 +108,7 @@ public class BigQueryExample {
 
   private abstract static class BigQueryAction<T> {
 
-    abstract void run(BigQuery bigquery, T request) throws Exception;
+    abstract void run(BigQuery bigquery, T arg) throws Exception;
 
     abstract T parse(String... args) throws Exception;
 
@@ -775,18 +775,18 @@ public static void main(String... args) throws Exception {
       return;
     }
     BigQuery bigquery = optionsBuilder.build().service();
-    Object request;
+    Object arg;
     try {
-      request = action.parse(args);
+      arg = action.parse(args);
     } catch (IllegalArgumentException ex) {
-      System.out.println("Invalid input for action '" + actionName + "'. " + ex.getMessage());
-      System.out.println("Expected: " + action.params());
+      System.out.printf("Invalid input for action '%s'. %s%n", actionName, ex.getMessage());
+      System.out.printf("Expected: %s%n", action.params());
       return;
     } catch (Exception ex) {
-      System.out.println("Failed to parse request.");
+      System.out.println("Failed to parse arguments.");
       ex.printStackTrace();
       return;
     }
-    action.run(bigquery, request);
+    action.run(bigquery, arg);
   }
 }