001 /* 002 * JOSMng - a Java Open Street Map editor, the next generation. 003 * 004 * Copyright (C) 2008 Petr Nejedly <P.Nejedly@sh.cvut.cz> 005 * 006 * This program is free software; you can redistribute it and/or modify 007 * it under the terms of the GNU General Public License as published by 008 * the Free Software Foundation; either version 2 of the License, or 009 * (at your option) any later version. 010 * 011 * This program is distributed in the hope that it will be useful, 012 * but WITHOUT ANY WARRANTY; without even the implied warranty of 013 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 014 * GNU General Public License for more details. 015 016 * You should have received a copy of the GNU General Public License along 017 * with this program; if not, write to the Free Software Foundation, Inc., 018 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA 019 */ 020 021 package org.openstreetmap.josm.data.osm; 022 023 /** 024 * An interface allowing injection of hashcode and equality implementation 025 * based on some inner state of an object for a set. 026 * It supports two type parameters to implement effective foreign key implementation 027 * inside (@link Storage}, but for basic use, both type parameters are the same. 028 * 029 * For use cases, see {@link Storage}. 030 * @author nenik 031 */ 032 public interface Hash<K,T> { 033 034 /** 035 * Get hashcode for given instance, based on some inner state of the 036 * instance. The returned hashcode should remain constant over the time, 037 * so it should be based on some instance invariant. 038 * 039 * @param k the object to compute hashcode for 040 * @return computed hashcode 041 */ 042 public int getHashCode(K k); 043 044 /** 045 * Compare two instances for semantic or lookup equality. For use cases 046 * where it compares different types, refer to {@link Storage}. 047 * 048 * @param k the object to compare 049 * @param t the object to compare 050 * @return true if the objects are semantically equivalent, or if k 051 * uniquely identifies t in given class. 052 */ 053 public boolean equals(K k, T t); 054 }