[GitHub] [flink] wuchong commented on a change in pull request #8360: [FLINK-12393][table-common] Add the user-facing classes of the new type system

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wuchong commented on a change in pull request #8360: [FLINK-12393][table-common] Add the user-facing classes of the new type system
URL: https://github.com/apache/flink/pull/8360#discussion_r282334560
 
 

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 File path: flink-table/flink-table-common/src/main/java/org/apache/flink/table/types/DataType.java
 ##########
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.table.types;
+
+import org.apache.flink.annotation.PublicEvolving;
+import org.apache.flink.table.api.DataTypes;
+import org.apache.flink.table.api.ValidationException;
+import org.apache.flink.table.types.logical.LogicalType;
+import org.apache.flink.util.Preconditions;
+
+import javax.annotation.Nullable;
+
+import java.io.Serializable;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Objects;
+
+/**
+ * Describes the data type of a value in the table ecosystem. Instances of this class can be used to
+ * declare input and/or output types of operations.
+ *
+ * <p>The {@link DataType} class has two responsibilities: declaring a logical type and giving hints
+ * about the physical representation of data to the optimizer. While the logical type is mandatory,
+ * hints are optional but useful at the edges to other APIs.
+ *
+ * <p>The logical type is independent of any physical representation and is close to the "data type"
+ * terminology of the SQL standard. See {@link org.apache.flink.table.types.logical.LogicalType} and
+ * its subclasses for more information about available logical types and their properties.
+ *
+ * <p>Physical hints are required at the edges of the table ecosystem. Hints indicate the data format
+ * that an implementation expects. For example, a data source could express that it produces values for
+ * logical timestamps using a {@link java.sql.Timestamp} class instead of using {@link java.time.LocalDateTime}.
+ * With this information, the runtime is able to convert the produced class into its internal data
+ * format. In return, a data sink can declare the data format it consumes from the runtime.
+ *
+ * @see DataTypes for a list of supported data types and instances of this class.
+ */
+@PublicEvolving
+public abstract class DataType implements Serializable {
+
+	protected LogicalType logicalType;
+
+	protected @Nullable Class<?> conversionClass;
+
+	private DataType(LogicalType logicalType, @Nullable Class<?> conversionClass) {
+		this.logicalType = Preconditions.checkNotNull(logicalType, "Logical type must not be null.");
+		this.conversionClass = performEarlyClassValidation(logicalType, conversionClass);
+	}
+
+	/**
+	 * Returns the corresponding logical type.
+	 *
+	 * @return a parameterized instance of {@link LogicalType}
+	 */
+	public LogicalType getLogicalType() {
+		return logicalType;
+	}
+
+	/**
+	 * Returns the corresponding conversion class for representing values. If no conversion class was
+	 * defined manually, the default conversion defined by the logical type is used.
+	 *
+	 * @see LogicalType#getDefaultConversion()
+	 *
+	 * @return the expected conversion class
+	 */
+	public Class<?> getConversionClass() {
+		if (conversionClass == null) {
+			return logicalType.getDefaultConversion();
+		}
+		return conversionClass;
+	}
+
+	/**
+	 * Adds a hint that null values are not expected in the data for this type.
+	 *
+	 * @return a new, reconfigured data type instance
+	 */
+	public abstract DataType notNull();
+
+	/**
+	 * Adds a hint that null values are expected in the data for this type (default behavior).
+	 *
+	 * <p>This method exists for explicit declaration of the default behavior or for invalidation of
+	 * a previous call to {@link #notNull()}.
+	 *
+	 * @return a new, reconfigured data type instance
+	 */
+	public abstract DataType andNull();
 
 Review comment:
   How about rename `andNull()` --> `asNullable()` and `notNull()` --> `asNotNull()`?

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