tikhomirov@148: /*
tikhomirov@148:  * Copyright (c) 2011 TMate Software Ltd
tikhomirov@148:  *  
tikhomirov@148:  * This program is free software; you can redistribute it and/or modify
tikhomirov@148:  * it under the terms of the GNU General Public License as published by
tikhomirov@148:  * the Free Software Foundation; version 2 of the License.
tikhomirov@148:  *
tikhomirov@148:  * This program is distributed in the hope that it will be useful,
tikhomirov@148:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
tikhomirov@148:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
tikhomirov@148:  * GNU General Public License for more details.
tikhomirov@148:  *
tikhomirov@148:  * For information on how to redistribute this software under
tikhomirov@148:  * the terms of a license other than GNU General Public License
tikhomirov@148:  * contact TMate Software at support@hg4j.com
tikhomirov@148:  */
tikhomirov@148: package org.tmatesoft.hg.util;
tikhomirov@148: 
tikhomirov@148: /**
tikhomirov@148:  * Extension mechanism.
tikhomirov@148:  * 
tikhomirov@148:  * @author Artem Tikhomirov
tikhomirov@148:  * @author TMate Software Ltd.
tikhomirov@148:  */
tikhomirov@148: public interface Adaptable {
tikhomirov@148: 
tikhomirov@148: 	<T> T getAdapter(Class<T> adapterClass);
tikhomirov@356: 
tikhomirov@356: 	class Factory<T> {
tikhomirov@356: 		
tikhomirov@356: 		private final Class<T> adapterClass;
tikhomirov@356: 
tikhomirov@356: 		public Factory(Class<T> adapterClass) {
tikhomirov@356: 			assert adapterClass != null;
tikhomirov@356: 			this.adapterClass = adapterClass;
tikhomirov@356: 		}
tikhomirov@356: 
tikhomirov@356: 		public T get(Object target) {
tikhomirov@356: 			return getAdapter(target, adapterClass, null);
tikhomirov@356: 		}
tikhomirov@356: 		
tikhomirov@356: 		public T get(Object target, T defaultValue) {
tikhomirov@356: 			return getAdapter(target, adapterClass, defaultValue);
tikhomirov@356: 		}
tikhomirov@356: 		
tikhomirov@356: 		/**
tikhomirov@356: 		 * Try to adapt target to specified class, resort to defaultValue when not possible.
tikhomirov@356: 		 * Instance lookup order is as follows: first, target is checked for being {@link Adaptable} and, if yes, 
tikhomirov@356: 		 * consulted for adapter. Then, plain {@link Class#isInstance(Object) instanceof} checks if target itself is
tikhomirov@356: 		 * of desired type. {@link Adaptable} check comes first to allow classed that are in fact <code>instanceof</code>
tikhomirov@356: 		 * desired type to respond to the demand conditionally
tikhomirov@356: 		 * 
tikhomirov@356: 		 * @param target object to adapt, <code>null</code> value, although meaningless, is tolerable.
tikhomirov@356: 		 * @param adapterClass desired target class
tikhomirov@356: 		 * @param defaultValue value to use if target cannot be adapted to desired class, may be <code>null</code>
tikhomirov@356: 		 * @return instance of the desired class
tikhomirov@356: 		 */
tikhomirov@356: 		public static <C> C getAdapter(Object target, Class<C> adapterClass, C defaultValue) {
tikhomirov@356: 			if (target instanceof Adaptable) {
tikhomirov@356: 				return ((Adaptable) target).getAdapter(adapterClass);
tikhomirov@356: 			}
tikhomirov@356: 			if (adapterClass.isInstance(target)) {
tikhomirov@356: 				return adapterClass.cast(target);
tikhomirov@356: 			}
tikhomirov@356: 			return defaultValue;
tikhomirov@356: 		}
tikhomirov@356: 	}
tikhomirov@148: }