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annotate src/org/tmatesoft/hg/util/CancelSupport.java @ 221:04735ce6bed2

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NPE when one of the flags is non-null
author Artem Tikhomirov <tikhomirov.artem@gmail.com>
date Thu, 19 May 2011 04:45:52 +0200
parents 41a778e3fd31
children f9f3e9b67ccc
rev   line source
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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 * Mix-in for objects that support cancellation.
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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 CancelSupport {
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26
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27 /**
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28 * This method is invoked to check if target had been brought to canceled state. Shall silently return if target is
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29 * in regular state.
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30 * @throws CancelledException when target internal state has been changed to canceled.
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31 */
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32 void checkCancelled() throws CancelledException;
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33
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34
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35 // Yeah, this factory class looks silly now, but perhaps in the future I'll need wrappers for other cancellation sources?
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36 // just don't want to have general Utils class with methods like get() below
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37 static class Factory {
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38
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39 /**
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40 * Obtain non-null cancel support object.
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41 *
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42 * @param target any object (or <code>null</code>) that might have cancel support. For <code>null</code>, returns an instance than never cancels.
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43 * @return target if it's capable checking cancellation status or no-op implementation that never cancels.
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44 */
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45 public static CancelSupport get(Object target) {
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46 if (target instanceof CancelSupport) {
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47 return (CancelSupport) target;
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48 }
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49 if (target instanceof Adaptable) {
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50 CancelSupport cs = ((Adaptable) target).getAdapter(CancelSupport.class);
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51 if (cs != null) {
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52 return cs;
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53 }
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54 }
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55 return new CancelSupport() {
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56 public void checkCancelled() {
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57 }
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58 };
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59 }
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60 }
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62 interface Target<T> {
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63 T set(CancelSupport cs);
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64 }
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65 }