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annotate src/org/tmatesoft/hg/util/Adaptable.java @ 356:91d75e1bac9f

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Consistent approach to deal with adaptable objects. Give adaptable precedence over instanceof to allow conditional response when classes do implement desired interface
author Artem Tikhomirov <tikhomirov.artem@gmail.com>
date Tue, 06 Dec 2011 14:25:52 +0100
parents 1a7a9a20e1f9
children
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1 /*
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2 * Copyright (c) 2011 TMate Software Ltd
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3 *
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4 * This program is free software; you can redistribute it and/or modify
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5 * it under the terms of the GNU General Public License as published by
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6 * the Free Software Foundation; version 2 of the License.
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7 *
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8 * This program is distributed in the hope that it will be useful,
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9 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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11 * GNU General Public License for more details.
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12 *
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13 * For information on how to redistribute this software under
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14 * the terms of a license other than GNU General Public License
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15 * contact TMate Software at support@hg4j.com
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16 */
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17 package org.tmatesoft.hg.util;
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18
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19 /**
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20 * Extension mechanism.
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21 *
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22 * @author Artem Tikhomirov
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23 * @author TMate Software Ltd.
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24 */
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25 public interface Adaptable {
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26
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27 <T> T getAdapter(Class<T> adapterClass);
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29 class Factory<T> {
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31 private final Class<T> adapterClass;
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33 public Factory(Class<T> adapterClass) {
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34 assert adapterClass != null;
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35 this.adapterClass = adapterClass;
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36 }
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38 public T get(Object target) {
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39 return getAdapter(target, adapterClass, null);
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40 }
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42 public T get(Object target, T defaultValue) {
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43 return getAdapter(target, adapterClass, defaultValue);
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44 }
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46 /**
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47 * Try to adapt target to specified class, resort to defaultValue when not possible.
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48 * Instance lookup order is as follows: first, target is checked for being {@link Adaptable} and, if yes,
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49 * consulted for adapter. Then, plain {@link Class#isInstance(Object) instanceof} checks if target itself is
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50 * of desired type. {@link Adaptable} check comes first to allow classed that are in fact <code>instanceof</code>
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51 * desired type to respond to the demand conditionally
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52 *
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53 * @param target object to adapt, <code>null</code> value, although meaningless, is tolerable.
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54 * @param adapterClass desired target class
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55 * @param defaultValue value to use if target cannot be adapted to desired class, may be <code>null</code>
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56 * @return instance of the desired class
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57 */
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58 public static <C> C getAdapter(Object target, Class<C> adapterClass, C defaultValue) {
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59 if (target instanceof Adaptable) {
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60 return ((Adaptable) target).getAdapter(adapterClass);
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61 }
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62 if (adapterClass.isInstance(target)) {
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63 return adapterClass.cast(target);
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64 }
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65 return defaultValue;
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66 }
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67 }
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68 }