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// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd
package com.google.protobuf;
import static com.google.protobuf.Internal.checkNotNull;
/**
* {@code SingleFieldBuilder} implements a structure that a protocol message uses to hold a single
* field of another protocol message. It supports the classical use case of setting an immutable
* {@link Message} as the value of the field and is highly optimized around this.
*
* It also supports the additional use case of setting a {@link Message.Builder} as the field and
* deferring conversion of that {@code Builder} to an immutable {@code Message}. In this way, it's
* possible to maintain a tree of {@code Builder}'s that acts as a fully read/write data structure.
*
* Logically, one can think of a tree of builders as converting the entire tree to messages when
* build is called on the root or when any method is called that desires a Message instead of a
* Builder. In terms of the implementation, the {@code SingleFieldBuilder} and {@code
* RepeatedFieldBuilder} classes cache messages that were created so that messages only need to be
* created when some change occurred in its builder or a builder for one of its descendants.
*
* @param the type of message for the field
* @param the type of builder for the field
* @param the common interface for the message and the builder
* @author [email protected] (Jon Perlow)
*/
public class SingleFieldBuilder<
MType extends GeneratedMessage,
BType extends GeneratedMessage.Builder,
IType extends MessageOrBuilder>
implements GeneratedMessage.BuilderParent {
// Parent to send changes to.
private GeneratedMessage.BuilderParent parent;
// Invariant: one of builder or message fields must be non-null.
// If set, this is the case where we are backed by a builder. In this case,
// message field represents a cached message for the builder (or null if
// there is no cached message).
private BType builder;
// If builder is non-null, this represents a cached message from the builder.
// If builder is null, this is the authoritative message for the field.
private MType message;
// Indicates that we've built a message and so we are now obligated
// to dispatch dirty invalidations. See GeneratedMessage.BuilderListener.
private boolean isClean;
public SingleFieldBuilder(MType message, GeneratedMessage.BuilderParent parent, boolean isClean) {
this.message = checkNotNull(message);
this.parent = parent;
this.isClean = isClean;
}
public void dispose() {
// Null out parent so we stop sending it invalidations.
parent = null;
}
/**
* Get the message for the field. If the message is currently stored as a {@code Builder}, it is
* converted to a {@code Message} by calling {@link Message.Builder#buildPartial} on it. If no
* message has been set, returns the default instance of the message.
*
* @return the message for the field
*/
@SuppressWarnings("unchecked")
public MType getMessage() {
if (message == null) {
// If message is null, the invariant is that we must be have a builder.
message = (MType) builder.buildPartial();
}
return message;
}
/**
* Builds the message and returns it.
*
* @return the message
*/
public MType build() {
// Now that build has been called, we are required to dispatch
// invalidations.
isClean = true;
return getMessage();
}
/**
* Gets a builder for the field. If no builder has been created yet, a builder is created on
* demand by calling {@link Message#toBuilder}.
*
* @return The builder for the field
*/
@SuppressWarnings("unchecked")
public BType getBuilder() {
if (builder == null) {
// builder.mergeFrom() on a fresh builder
// does not create any sub-objects with independent clean/dirty states,
// therefore setting the builder itself to clean without actually calling
// build() cannot break any invariants.
builder = (BType) message.newBuilderForType(this);
builder.mergeFrom(message); // no-op if message is the default message
builder.markClean();
}
return builder;
}
/**
* Gets the base class interface for the field. This may either be a builder or a message. It will
* return whatever is more efficient.
*
* @return the message or builder for the field as the base class interface
*/
@SuppressWarnings("unchecked")
public IType getMessageOrBuilder() {
if (builder != null) {
return (IType) builder;
} else {
return (IType) message;
}
}
/**
* Sets a message for the field replacing any existing value.
*
* @param message the message to set
* @return the builder
*/
@CanIgnoreReturnValue
public SingleFieldBuilder setMessage(MType message) {
this.message = checkNotNull(message);
if (builder != null) {
builder.dispose();
builder = null;
}
onChanged();
return this;
}
/**
* Merges the field from another field.
*
* @param value the value to merge from
* @return the builder
*/
@CanIgnoreReturnValue
public SingleFieldBuilder mergeFrom(MType value) {
if (builder == null && message == message.getDefaultInstanceForType()) {
message = value;
} else {
getBuilder().mergeFrom(value);
}
onChanged();
return this;
}
/**
* Clears the value of the field.
*
* @return the builder
*/
@SuppressWarnings("unchecked")
@CanIgnoreReturnValue
public SingleFieldBuilder clear() {
message =
(MType)
(message != null
? message.getDefaultInstanceForType()
: builder.getDefaultInstanceForType());
if (builder != null) {
builder.dispose();
builder = null;
}
onChanged();
// After clearing, parent is dirty, but this field builder is now clean and any changes should
// trickle up.
isClean = true;
return this;
}
/**
* Called when a the builder or one of its nested children has changed and any parent should be
* notified of its invalidation.
*/
private void onChanged() {
// If builder is null, this is the case where onChanged is being called
// from setMessage or clear.
if (builder != null) {
message = null;
}
if (isClean && parent != null) {
parent.markDirty();
// Don't keep dispatching invalidations until build is called again.
isClean = false;
}
}
@Override
public void markDirty() {
onChanged();
}
}