/**
* 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 org.waveprotocol.wave.client.common.util;
/**
* A sequence maintains an ordering of objects defined via successor and
* predecessor relationships.
*
* This interface is intended to provide read-only access. It is up to each
* implementation to define whether it can reflect live changes to the
* underlying state.
*
* @param <T> type of item in this sequence.
*/
public interface Sequence<T> {
/**
* @return true iff this sequence is empty.
*/
boolean isEmpty();
/** @return first object in this sequence. */
T getFirst();
/** @return the last object in this sequence. */
T getLast();
/**
* @return the object after {@code x}, or {@code null} if {@code x} is the
* last item.
*/
T getNext(T x);
/**
* @return the object before {@code x}, or {@code null} if {@code x} is the
* first item.
*/
T getPrevious(T x);
/**
* @return true if and only if {@code x} is in this sequence.
*/
boolean contains(T x);
}