Java tutorial
/********************************************************************************** * $URL:https://source.sakaiproject.org/svn/osp/trunk/presentation/api/src/java/org/theospi/portfolio/presentation/model/PresentationItemComparator.java $ * $Id:PresentationItemComparator.java 9134 2006-05-08 20:28:42Z chmaurer@iupui.edu $ *********************************************************************************** * * Copyright (c) 2005, 2006, 2008 The Sakai Foundation * * Licensed under the Educational Community 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.opensource.org/licenses/ECL-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.theospi.portfolio.presentation.model; import java.util.Comparator; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.sakaiproject.metaobj.shared.model.Id; public class PresentationItemComparator implements Comparator { protected final transient Log logger = LogFactory.getLog(getClass()); /** * Compares its two arguments for order. Returns a negative integer, * zero, or a positive integer as the first argument is less than, equal * to, or greater than the second.<p> * <p/> * The implementor must ensure that <tt>sgn(compare(x, y)) == * -sgn(compare(y, x))</tt> for all <tt>x</tt> and <tt>y</tt>. (This * implies that <tt>compare(x, y)</tt> must throw an exception if and only * if <tt>compare(y, x)</tt> throws an exception.)<p> * <p/> * The implementor must also ensure that the relation is transitive: * <tt>((compare(x, y)>0) && (compare(y, z)>0))</tt> implies * <tt>compare(x, z)>0</tt>.<p> * <p/> * Finally, the implementer must ensure that <tt>compare(x, y)==0</tt> * implies that <tt>sgn(compare(x, z))==sgn(compare(y, z))</tt> for all * <tt>z</tt>.<p> * <p/> * It is generally the case, but <i>not</i> strictly required that * <tt>(compare(x, y)==0) == (x.equals(y))</tt>. Generally speaking, * any comparator that violates this condition should clearly indicate * this fact. The recommended language is "Note: this comparator * imposes orderings that are inconsistent with equals." * * @param o1 the first object to be compared. * @param o2 the second object to be compared. * @return a negative integer, zero, or a positive integer as the * first argument is less than, equal to, or greater than the * second. * @throws ClassCastException if the arguments' types prevent them from * being compared by this Comparator. */ public int compare(Object o1, Object o2) { PresentationItemDefinition q1 = (PresentationItemDefinition) o1; PresentationItemDefinition q2 = (PresentationItemDefinition) o2; if (o1 == null && o2 == null) return 0; else if (o1 == null) return -1; else if (o2 == null) return 1; Id id1 = q1.getId() == null ? q1.getNewId() : q1.getId(); Id id2 = q2.getId() == null ? q2.getNewId() : q2.getId(); if (id1 == null && id2 != null) return -1; else if (id1 != null && id2 == null) return 1; else if (id1 != null && id1.equals(id2)) return 0; //if the ids are the same, should be the same object long ord1 = q1.getNewSequence(); long ord2 = q2.getNewSequence(); if (ord1 < ord2) return -1; if (ord1 > ord2) return 1; // they are equal, return opposite of order ord1 = q1.getSequence(); ord2 = q2.getSequence(); if (ord1 < ord2) return 1; if (ord1 > ord2) return -1; return 0; } }