org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector Maven / Gradle / Ivy
/**
* 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.hadoop.hive.serde2.objectinspector;
/**
* ObjectInspector helps us to look into the internal structure of a complex
* object.
*
* A (probably configured) ObjectInspector instance stands for a specific type
* and a specific way to store the data of that type in the memory.
*
* For native java Object, we can directly access the internal structure through
* member fields and methods. ObjectInspector is a way to delegate that
* functionality away from the Object, so that we have more control on the
* behavior of those actions.
*
* An efficient implementation of ObjectInspector should rely on factory, so
* that we can make sure the same ObjectInspector only has one instance. That
* also makes sure hashCode() and equals() methods of java.lang.Object directly
* works for ObjectInspector as well.
*/
public interface ObjectInspector extends Cloneable {
/**
* Category.
*
*/
public static enum Category {
PRIMITIVE, LIST, MAP, STRUCT, UNION
};
/**
* Returns the name of the data type that is inspected by this
* ObjectInspector. This is used to display the type information to the user.
*
* For primitive types, the type name is standardized. For other types, the
* type name can be something like "list", "map", java class
* names, or user-defined type names similar to typedef.
*/
String getTypeName();
/**
* An ObjectInspector must inherit from one of the following interfaces if
* getCategory() returns: PRIMITIVE: PrimitiveObjectInspector LIST:
* ListObjectInspector MAP: MapObjectInspector STRUCT: StructObjectInspector.
*/
Category getCategory();
}