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comparison org.eclipse.core.commands/src/org/eclipse/core/commands/common/HandleObject.d @ 12:bc29606a740c

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Added dwt-addons in original directory structure of eclipse.org
author Frank Benoit <benoit@tionex.de>
date Sat, 14 Mar 2009 18:23:29 +0100
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11:43904fec5dca 12:bc29606a740c
1 /*******************************************************************************
2 * Copyright (c) 2004, 2006 IBM Corporation and others.
3 * All rights reserved. This program and the accompanying materials
4 * are made available under the terms of the Eclipse Public License v1.0
5 * which accompanies this distribution, and is available at
6 * http://www.eclipse.org/legal/epl-v10.html
7 *
8 * Contributors:
9 * IBM Corporation - initial API and implementation
10 * Port to the D programming language:
11 * Frank Benoit <benoit@tionex.de>
12 *******************************************************************************/
13 module org.eclipse.core.commands.common.HandleObject;
14
15 import org.eclipse.core.internal.commands.util.Util;
16 import org.eclipse.core.commands.common.IIdentifiable;
17 import org.eclipse.core.commands.common.EventManager;
18 import java.lang.all;
19
20 /**
21 * <p>
22 * An object that can exist in one of two states: defined and undefined. This is
23 * used by APIs that want to give a handle to an object, even though the object
24 * does not fully exist yet. This way, users can attach listeners to objects
25 * before they come into existence. It also protects the API from users that do
26 * not release references when they should.
27 * </p>
28 * <p>
29 * To enforce good coding practice, all handle objects must implement
30 * <code>equals</code> and <code>toString</code>. Please use
31 * <code>string</code> to cache the result for <code>toString</code> once
32 * calculated.
33 * </p>
34 * <p>
35 * All handle objects are referred to using a single identifier. This identifier
36 * is a instance of <code>String</code>. It is important that this identifier
37 * remain unique within whatever context that handle object is being used. For
38 * example, there should only ever be one instance of <code>Command</code>
39 * with a given identifier.
40 * </p>
41 *
42 * @since 3.1
43 */
44 public abstract class HandleObject : EventManager,
45 IIdentifiable {
46
47 /**
48 * The constant integer hash code value meaning the hash code has not yet
49 * been computed.
50 */
51 private static const int HASH_CODE_NOT_COMPUTED = -1;
52
53 /**
54 * A factor for computing the hash code for all schemes.
55 */
56 private static const int HASH_FACTOR = 89;
57
58 /**
59 * The seed for the hash code for all schemes.
60 */
61 private static const int HASH_INITIAL;
62
63 static this(){
64 HASH_INITIAL =
65 //typeid(char[]).getHash(& HandleObject.classinfo.name );
66 java.lang.all.toHash(HandleObject.classinfo.name);
67 }
68 /**
69 * Whether this object is defined. A defined object is one that has been
70 * fully initialized. By default, all objects start as undefined.
71 */
72 protected /+transient+/ bool defined = false;
73
74 /**
75 * The hash code for this object. This value is computed lazily, and marked
76 * as invalid when one of the values on which it is based changes.
77 */
78 private /+transient+/ int hashCode = HASH_CODE_NOT_COMPUTED;
79
80 /**
81 * The identifier for this object. This identifier should be unique across
82 * all objects of the same type and should never change. This value will
83 * never be <code>null</code>.
84 */
85 protected /+final+/ String id;
86
87 /**
88 * The string representation of this object. This string is for debugging
89 * purposes only, and is not meant to be displayed to the user. This value
90 * is computed lazily, and is cleared if one of its dependent values
91 * changes.
92 */
93 protected /+transient+/ String string = null;
94
95 /**
96 * Constructs a new instance of <code>HandleObject</code>.
97 *
98 * @param id
99 * The id of this handle; must not be <code>null</code>.
100 */
101 protected this(String id) {
102 if (id is null) {
103 throw new NullPointerException(
104 "Cannot create a handle with a null id"); //$NON-NLS-1$
105 }
106
107 this.id = id;
108 }
109
110 /**
111 * Tests whether this object is equal to another object. A handle object is
112 * only equal to another handle object with the same id and the same class.
113 *
114 * @param object
115 * The object with which to compare; may be <code>null</code>.
116 * @return <code>true</code> if the objects are equal; <code>false</code>
117 * otherwise.
118 */
119 public override int opEquals(Object object) {
120 // Check if they're the same.
121 if (object is this) {
122 return true;
123 }
124
125 // Check if they're the same type.
126 if (!(cast(HandleObject)object)) {
127 return false;
128 }
129
130 // Check each property in turn.
131 final HandleObject handle= cast(HandleObject) object;
132 return Util.equals(id, handle.id)
133 && (this.classinfo is handle.classinfo);
134 }
135
136 public /+override+/ final String getId() {
137 return id;
138 }
139
140 /**
141 * Computes the hash code for this object based on the id.
142 *
143 * @return The hash code for this object.
144 */
145 public final override hash_t toHash() {
146 if (hashCode is HASH_CODE_NOT_COMPUTED) {
147 hashCode = HASH_INITIAL * HASH_FACTOR + Util.toHash(id);
148 if (hashCode is HASH_CODE_NOT_COMPUTED) {
149 hashCode++;
150 }
151 }
152 return hashCode;
153 }
154
155 /**
156 * Whether this instance is defined. A defined instance is one that has been
157 * fully initialized. This allows objects to effectively disappear even
158 * though other objects may still have references to them.
159 *
160 * @return <code>true</code> if this object is defined; <code>false</code>
161 * otherwise.
162 */
163 public final bool isDefined() {
164 return defined;
165 }
166
167 /**
168 * The string representation of this object -- for debugging purposes only.
169 * This string should not be shown to an end user.
170 *
171 * @return The string representation; never <code>null</code>.
172 */
173 public override abstract String toString();
174
175 /**
176 * Makes this object becomes undefined. This method should make any defined
177 * properties <code>null</code>. It should also send notification to any
178 * listeners that these properties have changed.
179 */
180 public abstract void undefine();
181 }