242 lines
8 KiB
Java
242 lines
8 KiB
Java
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// Protocol Buffers - Google's data interchange format
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// Copyright 2008 Google Inc. All rights reserved.
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// http://code.google.com/p/protobuf/
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following disclaimer
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// in the documentation and/or other materials provided with the
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// distribution.
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// * Neither the name of Google Inc. nor the names of its
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// contributors may be used to endorse or promote products derived from
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// this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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package com.google.protobuf;
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/**
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* {@code SingleFieldBuilder} implements a structure that a protocol
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* message uses to hold a single field of another protocol message. It supports
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* the classical use case of setting an immutable {@link Message} as the value
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* of the field and is highly optimized around this.
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* <br>
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* It also supports the additional use case of setting a {@link Message.Builder}
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* as the field and deferring conversion of that {@code Builder}
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* to an immutable {@code Message}. In this way, it's possible to maintain
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* a tree of {@code Builder}'s that acts as a fully read/write data
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* structure.
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* <br>
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* Logically, one can think of a tree of builders as converting the entire tree
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* to messages when build is called on the root or when any method is called
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* that desires a Message instead of a Builder. In terms of the implementation,
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* the {@code SingleFieldBuilder} and {@code RepeatedFieldBuilder}
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* classes cache messages that were created so that messages only need to be
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* created when some change occured in its builder or a builder for one of its
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* descendants.
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*
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* @param <MType> the type of message for the field
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* @param <BType> the type of builder for the field
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* @param <IType> the common interface for the message and the builder
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*
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* @author jonp@google.com (Jon Perlow)
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*/
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public class SingleFieldBuilder
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<MType extends GeneratedMessage,
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BType extends GeneratedMessage.Builder,
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IType extends MessageOrBuilder>
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implements GeneratedMessage.BuilderParent {
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// Parent to send changes to.
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private GeneratedMessage.BuilderParent parent;
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// Invariant: one of builder or message fields must be non-null.
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// If set, this is the case where we are backed by a builder. In this case,
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// message field represents a cached message for the builder (or null if
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// there is no cached message).
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private BType builder;
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// If builder is non-null, this represents a cached message from the builder.
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// If builder is null, this is the authoritative message for the field.
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private MType message;
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// Indicates that we've built a message and so we are now obligated
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// to dispatch dirty invalidations. See GeneratedMessage.BuilderListener.
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private boolean isClean;
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public SingleFieldBuilder(
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MType message,
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GeneratedMessage.BuilderParent parent,
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boolean isClean) {
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if (message == null) {
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throw new NullPointerException();
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}
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this.message = message;
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this.parent = parent;
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this.isClean = isClean;
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}
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public void dispose() {
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// Null out parent so we stop sending it invalidations.
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parent = null;
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}
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/**
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* Get the message for the field. If the message is currently stored
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* as a {@code Builder}, it is converted to a {@code Message} by
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* calling {@link Message.Builder#buildPartial} on it. If no message has
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* been set, returns the default instance of the message.
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*
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* @return the message for the field
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*/
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@SuppressWarnings("unchecked")
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public MType getMessage() {
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if (message == null) {
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// If message is null, the invariant is that we must be have a builder.
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message = (MType) builder.buildPartial();
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}
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return message;
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}
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/**
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* Builds the message and returns it.
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*
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* @return the message
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*/
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public MType build() {
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// Now that build has been called, we are required to dispatch
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// invalidations.
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isClean = true;
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return getMessage();
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}
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/**
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* Gets a builder for the field. If no builder has been created yet, a
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* builder is created on demand by calling {@link Message#toBuilder}.
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*
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* @return The builder for the field
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*/
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@SuppressWarnings("unchecked")
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public BType getBuilder() {
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if (builder == null) {
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// builder.mergeFrom() on a fresh builder
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// does not create any sub-objects with independent clean/dirty states,
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// therefore setting the builder itself to clean without actually calling
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// build() cannot break any invariants.
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builder = (BType) message.newBuilderForType(this);
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builder.mergeFrom(message); // no-op if message is the default message
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builder.markClean();
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}
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return builder;
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}
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/**
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* Gets the base class interface for the field. This may either be a builder
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* or a message. It will return whatever is more efficient.
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*
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* @return the message or builder for the field as the base class interface
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*/
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@SuppressWarnings("unchecked")
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public IType getMessageOrBuilder() {
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if (builder != null) {
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return (IType) builder;
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} else {
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return (IType) message;
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}
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}
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/**
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* Sets a message for the field replacing any existing value.
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*
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* @param message the message to set
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* @return the builder
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*/
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public SingleFieldBuilder<MType, BType, IType> setMessage(
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MType message) {
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if (message == null) {
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throw new NullPointerException();
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}
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this.message = message;
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if (builder != null) {
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builder.dispose();
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builder = null;
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}
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onChanged();
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return this;
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}
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/**
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* Merges the field from another field.
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*
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* @param value the value to merge from
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* @return the builder
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*/
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public SingleFieldBuilder<MType, BType, IType> mergeFrom(
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MType value) {
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if (builder == null && message == message.getDefaultInstanceForType()) {
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message = value;
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} else {
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getBuilder().mergeFrom(value);
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}
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onChanged();
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return this;
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}
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/**
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* Clears the value of the field.
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*
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* @return the builder
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*/
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@SuppressWarnings("unchecked")
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public SingleFieldBuilder<MType, BType, IType> clear() {
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message = (MType) (message != null ?
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message.getDefaultInstanceForType() :
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builder.getDefaultInstanceForType());
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if (builder != null) {
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builder.dispose();
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builder = null;
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}
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onChanged();
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return this;
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}
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/**
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* Called when a the builder or one of its nested children has changed
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* and any parent should be notified of its invalidation.
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*/
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private void onChanged() {
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// If builder is null, this is the case where onChanged is being called
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// from setMessage or clear.
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if (builder != null) {
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message = null;
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}
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if (isClean && parent != null) {
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parent.markDirty();
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// Don't keep dispatching invalidations until build is called again.
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isClean = false;
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}
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}
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//@Override (Java 1.6 override semantics, but we must support 1.5)
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public void markDirty() {
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onChanged();
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}
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}
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