/*
* Copyright 2010 Google Inc.
*
* 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 com.google.gwt.view.client;
/**
* <p>
* Implementors of {@link ProvidesKey} provide a key for list items, such that
* items that are to be treated as distinct (for example, for editing) have
* distinct keys.
* </p>
* <p>
* The key must implement a coherent set of {@link Object#equals(Object)} and
* {@link Object#hashCode()} methods such that if objects {@code A} and {@code
* B} are to be treated as identical, then {@code A.equals(B)}, {@code
* B.equals(A)}, and {@code A.hashCode() == B.hashCode()}. If {@code A} and
* {@code B} are to be treated as unequal, then it must be the case that {@code
* A.equals(B) == false} and {@code B.equals(A) == false}.
* </p>
*
* @param <T> the data type of records in the list
*/
public interface ProvidesKey<T> {
/**
* Get the key for a list item.
*
* @param item the list item
* @return the key that represents the item
*/
Object getKey(T item);
}