runtime/etiao/src/main/java/org/apache/edgent/runtime/etiao/graph/model/IdMapper.java

/*
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,
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"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.edgent.runtime.etiao.graph.model;

/**
 * A set of elements associated with unique identifiers.
 * 
 * Null element references cannot be part of the set. Attempting to add or 
 * to retrieve the id of a null element throws a NullPointerException.
 * 
 * @param <ID> the identifier type.
 */
interface IdMapper<ID> {
    /**
     * Adds the specified object to the collection and generates a unique 
     * identifier for that object.  If the object has already been added 
     * to the set, then returns its identifier.
     *    
     * @param o the object to add
     * @return a unique identifier associated with the object.
     */
    ID add(Object o);    

    /**
     * Adds the specified object to the collection and associates it with the
     * specified identifier.
     * <p>
     * If the object has already been added to the set with the same 
     * identifier, then returns its identifier.  If the object has already 
     * been added to the set with another identifier, then throw an 
     * {@code IllegalStateException}. 
     *    
     * @param o the object to add
     * @param id the associated identifier
     * @return the identifier associated with the object.
     * @throws IllegalStateException if the object has already been added to 
     *          the set with another identifier
     */
    ID add(Object o, ID id);

    /**
     * Returns the identifier associated to the specified object, or {@code null}
     * if the object is not associated with an identifier.
     *    
     * @param o the object to add
     * @return the identifier associated with the object.
     */
    ID getId(Object o);
}