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| 1 // Protocol Buffers - Google's data interchange format |
| 2 // Copyright 2008 Google Inc. All rights reserved. |
| 3 // https://developers.google.com/protocol-buffers/ |
| 4 // |
| 5 // Redistribution and use in source and binary forms, with or without |
| 6 // modification, are permitted provided that the following conditions are |
| 7 // met: |
| 8 // |
| 9 // * Redistributions of source code must retain the above copyright |
| 10 // notice, this list of conditions and the following disclaimer. |
| 11 // * Redistributions in binary form must reproduce the above |
| 12 // copyright notice, this list of conditions and the following disclaimer |
| 13 // in the documentation and/or other materials provided with the |
| 14 // distribution. |
| 15 // * Neither the name of Google Inc. nor the names of its |
| 16 // contributors may be used to endorse or promote products derived from |
| 17 // this software without specific prior written permission. |
| 18 // |
| 19 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| 20 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| 21 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| 22 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| 23 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| 24 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| 25 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| 26 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| 27 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| 28 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| 29 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| 30 |
| 31 package com.google.protobuf; |
| 32 |
| 33 /** |
| 34 * {@code SingleFieldBuilderV3} implements a structure that a protocol |
| 35 * message uses to hold a single field of another protocol message. It supports |
| 36 * the classical use case of setting an immutable {@link Message} as the value |
| 37 * of the field and is highly optimized around this. |
| 38 * <br> |
| 39 * It also supports the additional use case of setting a {@link Message.Builder} |
| 40 * as the field and deferring conversion of that {@code Builder} |
| 41 * to an immutable {@code Message}. In this way, it's possible to maintain |
| 42 * a tree of {@code Builder}'s that acts as a fully read/write data |
| 43 * structure. |
| 44 * <br> |
| 45 * Logically, one can think of a tree of builders as converting the entire tree |
| 46 * to messages when build is called on the root or when any method is called |
| 47 * that desires a Message instead of a Builder. In terms of the implementation, |
| 48 * the {@code SingleFieldBuilderV3} and {@code RepeatedFieldBuilderV3} |
| 49 * classes cache messages that were created so that messages only need to be |
| 50 * created when some change occurred in its builder or a builder for one of its |
| 51 * descendants. |
| 52 * |
| 53 * @param <MType> the type of message for the field |
| 54 * @param <BType> the type of builder for the field |
| 55 * @param <IType> the common interface for the message and the builder |
| 56 * |
| 57 * @author jonp@google.com (Jon Perlow) |
| 58 */ |
| 59 public class SingleFieldBuilderV3 |
| 60 <MType extends AbstractMessage, |
| 61 BType extends AbstractMessage.Builder, |
| 62 IType extends MessageOrBuilder> |
| 63 implements AbstractMessage.BuilderParent { |
| 64 |
| 65 // Parent to send changes to. |
| 66 private AbstractMessage.BuilderParent parent; |
| 67 |
| 68 // Invariant: one of builder or message fields must be non-null. |
| 69 |
| 70 // If set, this is the case where we are backed by a builder. In this case, |
| 71 // message field represents a cached message for the builder (or null if |
| 72 // there is no cached message). |
| 73 private BType builder; |
| 74 |
| 75 // If builder is non-null, this represents a cached message from the builder. |
| 76 // If builder is null, this is the authoritative message for the field. |
| 77 private MType message; |
| 78 |
| 79 // Indicates that we've built a message and so we are now obligated |
| 80 // to dispatch dirty invalidations. See AbstractMessage.BuilderListener. |
| 81 private boolean isClean; |
| 82 |
| 83 public SingleFieldBuilderV3( |
| 84 MType message, |
| 85 AbstractMessage.BuilderParent parent, |
| 86 boolean isClean) { |
| 87 if (message == null) { |
| 88 throw new NullPointerException(); |
| 89 } |
| 90 this.message = message; |
| 91 this.parent = parent; |
| 92 this.isClean = isClean; |
| 93 } |
| 94 |
| 95 public void dispose() { |
| 96 // Null out parent so we stop sending it invalidations. |
| 97 parent = null; |
| 98 } |
| 99 |
| 100 /** |
| 101 * Get the message for the field. If the message is currently stored |
| 102 * as a {@code Builder}, it is converted to a {@code Message} by |
| 103 * calling {@link Message.Builder#buildPartial} on it. If no message has |
| 104 * been set, returns the default instance of the message. |
| 105 * |
| 106 * @return the message for the field |
| 107 */ |
| 108 @SuppressWarnings("unchecked") |
| 109 public MType getMessage() { |
| 110 if (message == null) { |
| 111 // If message is null, the invariant is that we must be have a builder. |
| 112 message = (MType) builder.buildPartial(); |
| 113 } |
| 114 return message; |
| 115 } |
| 116 |
| 117 /** |
| 118 * Builds the message and returns it. |
| 119 * |
| 120 * @return the message |
| 121 */ |
| 122 public MType build() { |
| 123 // Now that build has been called, we are required to dispatch |
| 124 // invalidations. |
| 125 isClean = true; |
| 126 return getMessage(); |
| 127 } |
| 128 |
| 129 /** |
| 130 * Gets a builder for the field. If no builder has been created yet, a |
| 131 * builder is created on demand by calling {@link Message#toBuilder}. |
| 132 * |
| 133 * @return The builder for the field |
| 134 */ |
| 135 @SuppressWarnings("unchecked") |
| 136 public BType getBuilder() { |
| 137 if (builder == null) { |
| 138 // builder.mergeFrom() on a fresh builder |
| 139 // does not create any sub-objects with independent clean/dirty states, |
| 140 // therefore setting the builder itself to clean without actually calling |
| 141 // build() cannot break any invariants. |
| 142 builder = (BType) message.newBuilderForType(this); |
| 143 builder.mergeFrom(message); // no-op if message is the default message |
| 144 builder.markClean(); |
| 145 } |
| 146 return builder; |
| 147 } |
| 148 |
| 149 /** |
| 150 * Gets the base class interface for the field. This may either be a builder |
| 151 * or a message. It will return whatever is more efficient. |
| 152 * |
| 153 * @return the message or builder for the field as the base class interface |
| 154 */ |
| 155 @SuppressWarnings("unchecked") |
| 156 public IType getMessageOrBuilder() { |
| 157 if (builder != null) { |
| 158 return (IType) builder; |
| 159 } else { |
| 160 return (IType) message; |
| 161 } |
| 162 } |
| 163 |
| 164 /** |
| 165 * Sets a message for the field replacing any existing value. |
| 166 * |
| 167 * @param message the message to set |
| 168 * @return the builder |
| 169 */ |
| 170 public SingleFieldBuilderV3<MType, BType, IType> setMessage( |
| 171 MType message) { |
| 172 if (message == null) { |
| 173 throw new NullPointerException(); |
| 174 } |
| 175 this.message = message; |
| 176 if (builder != null) { |
| 177 builder.dispose(); |
| 178 builder = null; |
| 179 } |
| 180 onChanged(); |
| 181 return this; |
| 182 } |
| 183 |
| 184 /** |
| 185 * Merges the field from another field. |
| 186 * |
| 187 * @param value the value to merge from |
| 188 * @return the builder |
| 189 */ |
| 190 public SingleFieldBuilderV3<MType, BType, IType> mergeFrom( |
| 191 MType value) { |
| 192 if (builder == null && message == message.getDefaultInstanceForType()) { |
| 193 message = value; |
| 194 } else { |
| 195 getBuilder().mergeFrom(value); |
| 196 } |
| 197 onChanged(); |
| 198 return this; |
| 199 } |
| 200 |
| 201 /** |
| 202 * Clears the value of the field. |
| 203 * |
| 204 * @return the builder |
| 205 */ |
| 206 @SuppressWarnings("unchecked") |
| 207 public SingleFieldBuilderV3<MType, BType, IType> clear() { |
| 208 message = (MType) (message != null ? |
| 209 message.getDefaultInstanceForType() : |
| 210 builder.getDefaultInstanceForType()); |
| 211 if (builder != null) { |
| 212 builder.dispose(); |
| 213 builder = null; |
| 214 } |
| 215 onChanged(); |
| 216 return this; |
| 217 } |
| 218 |
| 219 /** |
| 220 * Called when a the builder or one of its nested children has changed |
| 221 * and any parent should be notified of its invalidation. |
| 222 */ |
| 223 private void onChanged() { |
| 224 // If builder is null, this is the case where onChanged is being called |
| 225 // from setMessage or clear. |
| 226 if (builder != null) { |
| 227 message = null; |
| 228 } |
| 229 if (isClean && parent != null) { |
| 230 parent.markDirty(); |
| 231 |
| 232 // Don't keep dispatching invalidations until build is called again. |
| 233 isClean = false; |
| 234 } |
| 235 } |
| 236 |
| 237 @Override |
| 238 public void markDirty() { |
| 239 onChanged(); |
| 240 } |
| 241 } |
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