[CALCITE-1959] Reduce the amount of metadata and tableName calls in D…

…ruid (Zain Humayun)

* Update javadocs
* Use correct create method in getTableMap

druid/src/main/java/org/apache/calcite/adapter/druid/DruidSchema.java

@@ -83,7 +83,7 @@ public DruidSchema(String url, String coordinatorUrl,
 
                     return DruidTable.create(DruidSchema.this, tableName, null,
                             fieldMap, metricNameSet, DruidTable.DEFAULT_TIMESTAMP_COLUMN,
-                            connection, complexMetrics);
+                            complexMetrics);
                   }
                 }));
     }

druid/src/main/java/org/apache/calcite/adapter/druid/DruidTable.java

@@ -91,17 +91,17 @@ public DruidTable(DruidSchema schema, String dataSource,
             : ImmutableMap.copyOf(allFields);
   }
 
-  /** Creates a {@link DruidTable}
+  /** Creates a {@link DruidTable} by using the given {@link DruidConnectionImpl}
+   * to populate the other parameters. The parameters may be partially populated.
    *
    * @param druidSchema Druid schema
    * @param dataSourceName Data source name in Druid, also table name
    * @param intervals Intervals, or null to use default
-   * @param fieldMap Mutable map of fields (dimensions plus metrics);
-   *        may be partially populated already
-   * @param metricNameSet Mutable set of metric names;
-   *        may be partially populated already
+   * @param fieldMap Partially populated map of fields (dimensions plus metrics)
+   * @param metricNameSet Partially populated set of metric names
    * @param timestampColumnName Name of timestamp column, or null
-   * @param connection connection used to find column definitions. Must be non-null.
+   * @param connection Connection used to find column definitions; Must be non-null
+   * @param complexMetrics List of complex metrics in Druid (thetaSketch, hyperUnique)
    *
    * @return A table
    */
@@ -118,16 +118,16 @@ static Table create(DruidSchema druidSchema, String dataSourceName,
             metricNameSet, timestampColumnName, complexMetrics);
   }
 
-  /** Creates a {@link DruidTable}
+  /** Creates a {@link DruidTable} by copying the given parameters.
    *
    * @param druidSchema Druid schema
    * @param dataSourceName Data source name in Druid, also table name
    * @param intervals Intervals, or null to use default
-   * @param fieldMap Mutable map of fields (dimensions plus metrics);
-   *        may be partially populated already
-   * @param metricNameSet Mutable set of metric names;
-   *        may be partially populated already
+   * @param fieldMap Fully populated map of fields (dimensions plus metrics)
+   * @param metricNameSet Fully populated set of metric names
    * @param timestampColumnName Name of timestamp column, or null
+   * @param complexMetrics List of complex metrics in Druid (thetaSketch, hyperUnique)
+   *
    * @return A table
    */
   static Table create(DruidSchema druidSchema, String dataSourceName,

druid/src/test/java/org/apache/calcite/test/DruidAdapterIT.java

@@ -48,6 +48,7 @@
 import static org.hamcrest.CoreMatchers.containsString;
 import static org.hamcrest.CoreMatchers.is;
 import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.assertTrue;
 
@@ -3191,7 +3192,7 @@ private void testCountWithApproxDistinct(boolean approx, String sql, String expe
    * */
   @Test public void testTableMapReused() {
     AbstractSchema schema = new DruidSchema("http://localhost:8082", "http://localhost:8081", true);
-    assert schema.getTable("wikiticker") == schema.getTable("wikiticker");
+    assertSame(schema.getTable("wikiticker"), schema.getTable("wikiticker"));
   }
 }