/***********************************************************************************************************************
* Copyright (C) 2010-2013 by the Stratosphere project (http://stratosphere.eu)
*
* Licensed 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 eu.stratosphere.types;
/**
* This interface has to be implemented by all data types that act as key. Keys are used to establish
* relationships between values. A key must always be {@link java.lang.Comparable} to other keys of
* the same type. In addition, keys must implement a correct {@link java.lang.Object#hashCode()} method
* and {@link java.lang.Object#equals(Object)} method to ensure that grouping on keys works properly.
* <p>
* This interface extends {@link eu.stratosphere.types.Value} and requires to implement
* the serialization of its value.
*
* @see eu.stratosphere.types.Value
* @see eu.stratosphere.core.io.IOReadableWritable
* @see java.lang.Comparable
*/
public interface Key<T> extends Value, Comparable<T> {
/**
* All keys must override the hash-code function to generate proper deterministic hash codes,
* based on their contents.
*
* @return The hash code of the key
*/
public int hashCode();
/**
* Compares the object on equality with another object.
*
* @param other The other object to compare against.
*
* @return True, iff this object is identical to the other object, false otherwise.
*/
public boolean equals(Object other);
}